Weather, season, and daily stroke admissions in Hong Kong

Heat, humidity and health impacts: how causal diagrams can help tell the complex story

The global health burden associated with exposure to heat is a grave concern and is projected to further increase under climate change. While physiological studies have demonstrated the role of humidity alongside temperature in exacerbating heat stress for humans, epidemiological findings remain conflicted. Understanding the intricate relationships between heat, humidity, and health outcomes is crucial to inform adaptation and drive increased global climate change mitigation efforts. This article introduces 'directed acyclic graphs' (DAGs) as causal models to elucidate the analytical complexity in observational epidemiological studies that focus on humid-heat-related health impacts. DAGs are employed to delineate implicit assumptions often overlooked in such studies, depicting humidity as a confounder, mediator, or an effect modifier. We also discuss complexities arising from using composite indices, such as wet-bulb temperature. DAGs representing the health impacts associated with wet-bulb temperature help to understand the limitations in separating the individual effect of humidity from the perceived effect of wet-bulb temperature on health. General examples for regression models corresponding to each of the causal assumptions are also discussed. Our goal is not to prioritize one causal model but to discuss the causal models suitable for representing humid-heat health impacts and highlight the implications of selecting one model over another. We anticipate that the article will pave the way for future quantitative studies on the topic and motivate researchers to explicitly characterize the assumptions underlying their models with DAGs, facilitating accurate interpretations of the findings. This methodology is applicable to similarly complex compound events.

Short-Term Effect of Ambient Temperature in Acute Ischemic Stroke with Endovascular Treatment Due to Large Vessel Occlusion

Purpose

Acute ischemic stroke (AIS) stands as the primary cause of mortality and extended disability globally. While prior studies have examined the connection between stroke and local weather, they have produced conflicting results. Our goal was to examine the correlation between temperature and functional prognosis in patients with large vessel occlusion (LVO) undergoing endovascular therapy (EVT).

Patients and methods

This study included a total of 1809 patients. Temperatures from stroke onset to groin puncture were categorized into Cold (10th percentile of temperature), Cool (10th-50th percentile of temperature), Warm (50th-90th percentile of temperature), and Hot (90th percentile of temperature) groups. The primary efficacy result was the modified Rankin Scale (mRS) score at 90 days. Safety outcomes included mortality, symptomatic intracranial hemorrhage (sICH) and complications after cerebral infarction.

Results

The primary efficacy results demonstrated a statistical enhancement in functional outcomes at 90 days for patients in the Warm group compared to the Cold group (adjusted common odds ratio [OR]: 1.386; 95% confidence interval [CI]: 1.024-1.878, P=0.035). Secondary efficacy results showed that temperature was associated with a higher rate of 90-day functional independence (adjusted OR: 1.016; 95% CI: 1.004-1.029; P=0.009), which was higher in the Warm group compared with patients in the Cold group (adjusted OR: 1.646; 95% CI: 1.107-2.448, P=0.014). There were no significant differences between groups in terms of sICH, 90-day mortality, and post-infarction complications.

Conclusion

Compared with Cold temperature, Warm temperature is associated with better functional outcomes and reduced mortality risk without increasing the risk of sICH.

Association between ambient temperature and stroke risk in high-risk populations: a systematic review

Background

Significant associations exist between ambient temperature and stroke risk, but results in high cardiovascular risk populations are lacking. This systemic review summarised current evidence on ambient temperature and overall stroke risk in a high cardiovascular risk population.

Methods

We performed a systematic literature search across MEDLINE, Embase, PsycINFO, CINAHL, Web of Science, and GEOBASE, from inception to 3 July 2023, to identify all population-based studies. Eligible studies screened by independent reviewers recruited individuals aged 18 years and over, where minimum 80% of participants had a high cerebral vascular disease (CVD) risk profile. The primary outcomes are stroke morbidity and mortality, while the secondary outcomes are morbidity and mortality of ischaemic stroke (IS), intracranial cerebral haemorrhage (ICH), and subarachnoid haemorrhage (SH).

Results

The database searches identified 9,025 articles. After removing duplicates, 7,647 articles were screened in title and abstract to identify 380 articles for full-text screening. After the full-text screening of 380 articles by two independent reviewers, 23 articles were included in the review.

Conclusion

The evidence for an association between ambient temperature and stroke incidence is that lower temperatures were more likely to increase morbidity and mortality risk of both haemorrhagic and ischaemic stroke in older people. Conversely, higher ambient temperature is significantly associated with intracranial haemorrhage risk, but decreased risk with IS. Higher and lower ambient temperatures consistently increase stroke risks in patients with comorbidities of congestive heart failure and dyslipidaemia. This evidence implies the need to establish clinical guidelines for preventive intervention in patients with high stroke risks during extreme ambient temperatures.

Urban climate and cardiovascular health: Focused on seasonal variation of urban temperature, relative humidity, and PM2.5 air pollution

Seasonal effects on subclinical cardiovascular functions (CVFs) are an important emerging health issue for people living in urban environment. The objectives of this study were to demonstrate the effects of seasonal variations of temperature, relative humidity, and PM2.5 air pollution on CVFs. A total of 86 office workers in Taipei City were recruited, their arterial pressure waveform was recorded by cuff sphygmomanometer using an oscillometric blood pressure (BP) device for CVFs assessment. Results of paried t-test with Bonferroni correction showed significantly increased systolic and diastolic BP (SBP, DBP), central end-systolic and diastolic BP (cSBP, cDBP) and systemic vascular resistance, but decreased heart rate (HR), stroke volume (SV), cardio output (CO), and cardiac index in winter compared with other seasons. After controlling for related confounding factors, SBP, DBP, cSBP, cDBP, LV dp/dt max, and brachial-ankle pulse wave velocity (baPWV) were negatively associated with, and SV was positively associated with seasonal temperature changes. Seasonal changes of air pollution in terms of PM2.5 were significantly positively associated with DBP and cDBP, as well as negatively associated with HR and CO. Seasonal changes of relative humidity were significantly negatively associated with DBP, and cDBP, as well as positively associated with HR, CO, and baPWV. This study provides evidence of greater susceptibility to cardiovascular events in winter compared with other seasons, with ambient temperature, relative humidity, and PM2.5 as the major factors of seasonal variation of CVFs.

Climate and human health: a review of publication trends in the International Journal of Biometeorology

The climate-health nexus is well documented in the field of biometeorology. Since its inception, Biometeorology has in many ways become the umbrella under which much of this collaborative research has been conducted. Whilst a range of review papers have considered the development of biometeorological research and its coverage in this journal, and a few have reviewed the literature on specific diseases, none have focused on the sub-field of climate and health as a whole. Since its first issue in 1957, the International Journal of Biometeorology has published a total of 2183 papers that broadly consider human health and its relationship with climate. In this review, we identify a total of 180 (8.3%, n = 2183) of these papers that specifically focus on the intersection between meteorological variables and specific, named diagnosable diseases, and explore the publication trends thereof. The number of publications on climate and health in the journal increases considerably since 2011. The largest number of publications on the topic was in 2017 (18) followed by 2021 (17). Of the 180 studies conducted, respiratory diseases accounted for 37.2% of the publications, cardiovascular disease 17%, and cerebrovascular disease 11.1%. The literature on climate and health in the journal is dominated by studies from the global North, with a particular focus on Asia and Europe. Only 2.2% and 8.3% of these studies explore empirical evidence from the African continent and South America respectively. These findings highlight the importance of continued research on climate and human health, especially in low- and lower-middle-income countries, the populations of which are more vulnerable to climate-sensitive illnesses.

Humidity's Role in Heat-Related Health Outcomes: A Heated Debate

BACKGROUND

As atmospheric greenhouse gas concentrations continue to rise, temperature and humidity will increase further, causing potentially dire increases in human heat stress. On physiological and biophysical grounds, exposure to higher levels of humidity should worsen heat stress by decreasing sweat evaporation. However, population-scale epidemiological studies of heat exposure and response often do not detect associations between high levels of humidity and heat-related mortality or morbidity. These divergent, disciplinary views regarding the role of humidity in heat-related health risks limit confidence in selecting which interventions are effective in reducing health impacts and in projecting future heat-related health risks.

OBJECTIVES

Via our multidisciplinary perspective we seek to a) reconcile the competing realities concerning the role of humidity in heat-related health impacts and b) help ensure robust projections of heat-related health risks with climate change. These objectives are critical pathways to identify and communicate effective approaches to cope with present and future heat challenges.

DISCUSSION

We hypothesize six key reasons epidemiological studies have found little impact of humidity on heat-health outcomes: a) At high temperatures, there may be limited influence of humidity on the health conditions that cause most heat-related deaths (i.e., cardiovascular collapse); b) epidemiological data sets have limited spatial extent, a bias toward extratropical (i.e., cooler and less humid), high-income nations, and tend to exist in places where temporal variations in temperature and humidity are positively correlated; c) analyses focus on older, vulnerable populations with sweating, and thus evaporative, impairments that may be further aggravated by dehydration; d) extremely high levels of temperature and humidity (seldom seen in the historical record) are necessary for humidity to substantially impact heat strain of sedentary individuals; e) relationships between temperature and humidity are improperly considered when interpreting epidemiological model results; and f) sub-daily meteorological phenomena, such as rain, occur at high temperatures and humidity, and may bias epidemiological studies based on daily data. Future research must robustly test these hypotheses to advance methods for more accurate incorporation of humidity in estimating heat-related health outcomes under present and projected future climates. https://doi.org/10.1289/EHP11807.

Risk of ischemic and hemorrhagic stroke in relation to cold spells in four seasons

BACKGROUND

Cold winter weather increases the risk of stroke, but the evidence is scarce on whether the risk increases during season-specific cold weather in the other seasons. The objective of our study was to test the hypothesis of an association between personal cold spells and different types of stroke in the season-specific context, and to formally assess effect modification by age and sex.

METHODS

We conducted a case-crossover study of all 5396 confirmed 25-64 years old cases with stroke in the city of Kaunas, Lithuania, 2000-2015. We assigned to each case a one-week hazard period and 15 reference periods of the same calendar days of other study years. A personal cold day was defined for each case with a mean temperature below the fifth percentile of the frequency distribution of daily mean temperatures of the hazard and reference periods. Conditional logistic regression was applied to estimate odds ratios (OR) and 95% confidence intervals (95% CI) representing associations between time- and place-specific cold weather and stroke.

RESULTS

There were positive associations between cold weather and stroke in Kaunas, with each additional cold day during the week before the stroke increases the risk by 3% (OR 1.03; 95% CI 1.00-1.07). The association was present for ischemic stroke (OR 1.05; 95% CI 1.01-1.09) but not hemorrhagic stroke (OR 0.98; 95% CI 0.91-1.06). In the summer, the risk of stroke increased by 8% (OR 1.08; 95% CI 1.00-1.16) per each additional cold day during the hazard period. Age and sex did not modify the effect.

CONCLUSIONS

Our findings show that personal cold spells increase the risk of stroke, and this pertains to ischemic stroke specifically. Most importantly, cold weather in the summer season may be a previously unrecognized determinant of stroke.

The influence of meteorological factors and total malignant tumor health risk in Wuhu city in the context of climate change

With the increasing severity of the malignant tumors situation worldwide, the impacts of climate on them are receiving increasing attention. In this study, for the first time, all-malignant tumors were used as the dependent variable and absolute humidity (AH) was innovatively introduced into the independent variable to investigate the relationship between all-malignant tumors and meteorological factors. A total of 42,188 cases of malignant tumor deaths and meteorological factors in Wuhu City were collected over a 7-year (2014-2020) period. The analysis method combines distributed lagged nonlinear modeling (DLNM) as well as generalized additive modeling (GAM), with prior pre-analysis using structural equation modeling (SEM). The results showed that AH, temperature mean (T mean) and diurnal temperature range (DTR) all increased the malignant tumors mortality risk. Exposure to low and exceedingly low AH increases the malignant tumors mortality risk with maximum RR values of 1.008 (95% CI: 1.001, 1.015, lag 3) and 1.016 (95% CI: 1.001, 1.032, lag 1), respectively. In addition, low and exceedingly low T mean exposures also increased the risk of malignant tumors mortality, the maximum RR was 1.020 (95% CI: 1.006, 1.034) for low T mean and 1.035 (95% CI: 1.014, 1.058) for exceedingly low T mean. As for DTR, all four levels (exceedingly low, low, high, exceedingly high, from low to high) of exposure increased the risk of death from malignant tumors, from exceedingly low to exceedingly high maximum RR values of 1.018 (95% CI: 1.004, 1.032), 1.011 (95% CI: 1.005, 1.017), 1.006 (95% CI: 1.001, 1.012) and 1.019 (95% CI: 1.007, 1.031), respectively. The results of the stratified analysis suggested that female appear to be more sensitive to humidity, while male require additional attention to reduce exposure to high level of DTR.

The role of meteorological factors in suicide mortality in Wuhu, a humid city along the Yangtze River in Eastern China

As the climate continues to change, suicide is becoming more frequent. In this study, absolute humidity (AH) was included for the first time and Wuhu, a typical subtropical city along the Yangtze River, was taken as the research object to explore the impact of suicide death risk on meteorological factors. The daily meteorological factors and suicide mortality data of Wuhu city from 2014 to 2020 were collected. Guided by structural equation model (SEM), a time series analysis method combining distributed lag nonlinear model (DLNM) and generalized additive model (GAM) was adopted. To investigate the correlation among different populations, we stratified age and gender at different meteorological levels. A total of 1259 suicide deaths were collected in Wuhu. The results indicated that exceedingly low and low levels of AH short-term exposure increased suicide mortality, with the maximum effect occurring at lag 14 for both levels of exposure, when the relative risk (RR) was 1.131 (95% CI: 1.030, 1.242) and 1.065 (95% CI: 1.006, 1.127), respectively. Exposure to exceedingly high and exceedingly low levels of temperature mean (T mean) also increased suicide mortality, with maximum RR values of 1.132 (lag 14, 95% CI: 1.015, 1.263) and 1.203 (lag 0, 95% CI: 1.079, 1.340), sequentially. As for diurnal temperature range (DTR), low-level exposure decreased the risk of suicide, while high-level exposure increased this risk, with RR values of 0.955 (lag 0, 95% CI: 0.920, 0.991, minimum) and 1.060 (lag 0, 95% CI: 1.018, 1.104, maximum), sequentially. Stratified analysis showed that AH and DTR increased the suicide death risk in male and elderly people, while the risk effect of T mean have no effect on young people only. In summary, male and elderly people appear to be more vulnerable to adverse weather effects.

Associations of ambient temperature with mortality for ischemic and hemorrhagic stroke and the modification effects of greenness in Shandong Province, China

BACKGROUND

Evidence is scant on the relative and attributable contributions of ambient temperature on stroke subtypes mortality. Few studies have examined modification effects of multiple greenness indicators on such contributions, especially in China. We quantified the associations between ambient temperature and overall, ischemic, and hemorrhagic stroke mortality; further examined whether the associations were modified by greenness.

METHODS

We conducted a multicenter time-series analysis from January 1, 2013 to December 31, 2019. we adopted a distributed lag non-linear model to evaluate county-specific temperature-stroke mortality associations. We then applied a random-effects meta-analysis to pool county-specific effects. Attributable mortality was calculated for cold and heat, defined as temperatures below and above the minimum mortality temperature (MMT). Finally, We conducted a multivariate meta-regression to determine associations between greenness and stroke mortality risks for cold and heat, using normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and enhanced vegetation index (EVI) as quantitative indicators of greenness exposure.

RESULTS

In the study period, 138,749 deaths from total stroke were reported: 86,873 ischemic and 51,876 hemorrhagic stroke. We observed significant W-shaped relationships between temperature and stroke mortality, with substantial differences among counties and regions. With MMT as the temperature threshold, 17.16 % (95 % empirical CI, 13.38 %-19.75 %) of overall, 20.05 % (95 % eCI, 16.46 %-22.70 %) of ischemic, and 12.55 % (95 % eCI, 5.59 %-16.24 %) of hemorrhagic stroke mortality were attributable to non-optimum temperature (combining cold and heat), more mortality was caused by cold (14.94 %; 95 % eCI, 11.57 %-17.34 %) than by heat (2.22 %; 95 % eCI, 1.54 %-2.72 %). Higher levels of NDVI, SAVI and EVI were related to mitigated effects of non-optimum temperatures-especially heat.

CONCLUSIONS

Exposure to non-optimum temperatures aggravated stroke mortality risks; increasing greenness could alleviate that risks. This evidence has important implications for local communities in developing adaptive strategies to minimize the health consequences of adverse temperatures.

Effect of ambient temperature and other environmental factors on stroke emergency department visits in Beijing: A distributed lag non-linear model

Background

Most studies have focused on the relationship between ambient temperature and stroke mortality, but studies on the relationship between ambient temperature and stroke occurrence are still limited and inconsistent.

Objective

This study aimed to analyze the effect of ambient temperature and other environmental factors on emergency stroke visits in Beijing.

Methods

Our study utilized stroke visit data from the Beijing Red Cross Emergency Medical Center during 2017-2018, and applied a generalized additive model (GAM) as well as a distributed lag non-linear model (DLNM), respectively, regarding the direct, lagged, and cumulative effects of ambient temperature alone and with correction for other environmental factors on stroke occurrence.

Results

With a total of 26,984 emergency stroke patients in 2017-2018, both cold and hot effects were observed and weakened after correction for other environmental factors. Compared to the reference temperature, in the multi-factor model, extreme cold (-10°C) reached a maximum relative risk (RR) of 1.20 [95% Confidence Interval (CI): 1.09, 1.32] at lag 14 days, and extreme hot (30°C) had a maximum RR of 1.07 (95% CI: 1.04, 1.11) at lag 6 days. The cumulative effect of extreme cold reached a maximum of 2.02 (95% CI: 1.11, 3.67) at lag 0-14 days, whereas the cumulative effect of extreme hot temperature is greatest at lag 0-10 days, but no statistically significant effect was found. In addition, ischemic stroke patients, the elderly, and males were more susceptible to the effects of cold temperature.

Conclusions

There is a non-linear relationship between ambient temperature and stroke occurrence, with cold temperature having a greater and longer-lasting impact than hot temperature.

Exposure to air pollution and its effect on ischemic strokes (EP-PARTICLES study)

It is well known that exceeded levels of particulate matter in the air and other air pollutants harmfully affect the cardiovascular system. Empirical analyses of the effects of these factors on stroke incidence and mortality are still limited. The main objective of our analyses was to determine the association between short-term exposure to air pollutants and stroke incidence in non-industrial areas, more specifically in north-eastern Poland. To achieve this aim, we used data from the National Health Fund on patients hospitalized for stroke between 2011 and 2020 in the largest city of the region described as the Green Lungs of Poland. The pollution levels and atmospheric conditions data were obtained from the Provincial Inspectorate for Environmental Protection and the Institute of Meteorology and Water Management. Using daily data on hospitalizations, atmospheric conditions, and pollution, as well as ordered logistic regression models the hypotheses on the impact of weather and air pollution conditions on ischemic strokes were tested. The study group included 4838 patients, 45.6% of whom were male; the average patient age was approximately 74 years. The average concentrations of PM_2.5 were 19.09 µg/m³, PM₁₀ 26.66 µg/m³ and CO 0.35 µg/m³. Analyses showed that an increase in PM_2.5 and PM₁₀ concentrations by 10 µg/m³ was associated with an increase in the incidence of stroke on the day of exposure (OR = 1.075, 95% CI 0.999-1.157, P = 0.053; OR = 1.056, 95% CI 1.004-1.110, P = 0.035) and the effect was even several times greater on the occurrence of a stroke event in general (PM_2.5: OR = 1.120, 95% CI 1.013-1.237, P = 0.026; PM₁₀: OR = 1.103, 95% CI 1.028-1.182, P = 0.006). Furthermore, a short-term (up to 3 days) effect of CO on stroke incidence was observed in the study area. An increase of 1 μg/m³ CO was associated with a lower incidence of stroke 2 days after the exposure (OR = 0.976, 95% CI 0.953-0.998, P = 0.037) and a higher incidence 3 days after the exposure (OR = 1.026, 95% CI 1.004-1.049, P = 0.022).

Seasonal variation in the detection rate and all-cause in-hospital mortality of AKI in China: A nationwide cohort study

Background

Acute kidney injury (AKI) is a severe clinical syndrome that places a massive burden on medical systems worldwide, yet the seasonality of AKI remains unexplored in China. The aim of this study was to describe the seasonal variation in the detection rate and all-cause in-hospital mortality of AKI in China based on a nationwide cohort study.

Methods

This was a retrospective cohort recruiting a national sample of 7,291 adult patients treated in hospitals in 22 provinces of mainland China during January or July 2013. AKI was defined according to the 2012 Kidney Disease Improving Global Outcomes AKI creatinine criteria or expanded criteria of increase or decrease in serum creatinine level of 50% during the hospital stay. The seasonal group was determined according to the corresponding admission date for each patient. The detection rate of AKI refers to the ratio of identified AKI cases to the total number of adult admissions from the same regional or seasonal group.

Results

Both the detection rate (2.31 vs. 2.08%, p = 0.001) and in-hospital mortality rate (13.3 vs. 10.7%, p = 0.001) of AKI were higher in winter than in summer. The patients with AKI detected in winter had higher proportions of prehistory diseases, cardiac or vascular kidney injury factors, and severe comorbidities than those in summer (all p < 0.05). In the multivariable analysis, winter was an independent risk factor for in-hospital mortality of patients with AKI [odds ratio (OR) = 1.22, 95% confidence interval (CI), 1.03-1.44, p = 0.02] after adjusting for demographic factors, medical history, comorbidity, and climatic confounders. Higher ambient temperature (OR = 0.91, 95% CI, 0.86-0.97, p = 0.002, per 10°C increase), higher relative humidity level (OR = 1.14, 95% CI, 1.04-1.25, p = 0.005, per 10% increase), and living in temperate continental region (OR = 2.18, 95% CI, 1.63-2.91, p < 0.001) were each independently associated with in-hospital mortality.

Conclusion

The detection rate and all-cause in-hospital mortality of AKI showed a winter predominance in patients with AKI in China. Winter appeared to be an independent risk factor for all-cause in-hospital mortality in patients with AKI. Environmental factors, including lower ambient temperature, higher relative humidity level, and living in temperate continental climatic regions, were each independently associated with increased risks of in-hospital mortality in patients with AKI.

Do Meteorological Variations and Climate Changes Affect Hyperemesis Gravidarum?

Background To estimate a possible association between the effects of daily meteorological variation and climatological changes (temperature, air pressure, humidity, sunniness level) on pregnant women with hyperemesis gravidarum (HG) according to symptoms grade and hospitalization state.

Methods A retrospective study was conducted with 118 patients diagnosed and hospitalized with HG. HG patients were graded as mild, moderate, or severe according to the Pregnancy Unique Quantification of Emesis (PUQE-24) scale. Data regarding demographic characteristics, PUQE scale value, gestational week on hospitalization, hospital admission and discharge dates, weather conditions, daily meteorological values during hospitalization ( temperature, air pressure, humidity, sunniness level), seasonal averages, and daily changes were recorded. Weather records were obtained from the Ankara Meteorology General Directorate (Ankara, Turkey). Differences between groups were compared according to HG grade.

Results HG cases were classified as mild (33.1%), moderate (44.9%), or severe (22.0%). The number of hospitalization days significantly differed between these three groups (p<0.05). In contrast, no statistically significant differences were identified between the HG grade level groups in regard to humidity, pressure, temperature, and sunniness level data (p>0.05). In addition, no statistically significant relationship was identified between HG grades and seasonal conditions according to the chi-square test (p>0.05).

Conclusion Changes in the meteorological and climate values examined were independent of symptom severity and hospitalization rate for our HG patients. However, it is possible that climate changes occurring around the world may affect the pregnancy period and should be further investigated.

Relationship between diurnal temperature range and emergency ambulance dispatches due to stroke in Guangzhou, China

BACKGROUND

The evidence between diurnal temperature range (DTR) and stroke remains controversial and sparse. We aimed to assess the relationship between DTR and emergency ambulance dispatches (EADs) due to stroke, and to explore whether there were effect modifications to the relationship.

METHODS

A Quasi-Poisson generalized linear regression combined with a distributed lag non-linear model was used to examine the relationship between DTR and EADs for stroke between January 1st 2011 and June 30th 2018 in Guangzhou, China. We estimated the effects of the low DTR and high DTR (defined as DTR below and above 10 °C respectively) on EADs. The effects of minimum, maximum, 5th, 25th, 50th, 75th, and 95th percentiles of DTR compared with the DTR of 10 °C were also analyzed.

RESULTS

A total of 20,275 EADs for stroke were included for analyses, among which 17,556 EADs were used in the model further adjusted for age and sex. A quasi-U-shaped relationship between DTR and EADs over lag0-2 days was observed. For the low DTR, per 1 °C decrease in DTR was significantly associated with an increase of 2.64% (RR = 1.03, 95% CI: 1.01-1.04) for EADs, while per 1 °C increase for the high DTR was non-significantly related with an increased risk of EADs (RR = 1.01, 95% CI: 0.90-1.13). Significant effects of the 5th and 25th percentiles of DTR on EADs were found when compared with the DTR of 10 °C. No significant effect modifications by age, sex or season were found to the association between DTR and EADs.

CONCLUSIONS

We found a quasi-U-shaped relationship between DTR and EADs due to stroke in this study, while age, sex or season did not significantly modify the association between DTR and EADs. More high-quality evidence is needed to further explore and validate the relationship between DTR and stroke.

Short-term exposure to high relative humidity increases blood urea and influences colonic urea-nitrogen metabolism by altering the gut microbiota

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Plasma urea was increased along with erythrocyte Na⁺/K⁺ -ATPase activity reduced and abnormal erythrocyte morphologies appeared during 14-day high relative humidity (90 ± 2%) exposure.

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Shortly after 12-h and 24-h exposures, urea influx and ammonia level were increased in the colon of mice, respectively.

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Colonic urea-nitrogen metabolism was influenced by the increased levels of ammonia, amino acids and short-chain fatty acids during 14-day exposure.

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Gut bacteria related to urease production, amino acids metabolism and SCFAs production was enriched during the exposure.

Introduction

Colonic urea-nitrogen metabolites have been implicated in the pathogenesis of certain diseases which can be affected by environmental factors.

Objectives

We aimed to explore the influence of ambient humidity on colonic urea-nitrogen metabolism.

Methods

Blood biochemical indexes, metabolites of intestinal tract, and gut microbiota composition of mice (n = 10/group) exposed to high relative humidity (RH, 90 ± 2%) were analyzed during the 14-day exposure.

Results

After 12-h exposure, plasma blood urea nitrogen (BUN) level increased along with a decrease in the activity of erythrocyte Na⁺/K⁺ -ATPase. Moreover, abnormal erythrocyte morphologies appeared after 3 days of exposure. The colonic BUN and ammonia levels increased significantly after the 12-h and 24-h exposure, respectively. The colonic level of amino acids, partly synthesized by gut microbiota using ammonia as the nitrogen source, was significantly higher on the 7th day. Furthermore, the level of fecal short-chain fatty acids was significantly higher after 3-day exposure and the level of branched-chain fatty acids increased on the 14th day. Overall, gut microbiota composition was continuously altered during exposure, facilitating the preferential proliferation of urea-nitrogen metabolism bacteria.

Conclusion

Our findings suggest that short-term high RH exposure influences colonic urea-nitrogen metabolism by increasing the influx of colonic urea and altering gut microbiota, which might further impact the host health outcomes.

Relationship of Ambient Temperature Parameters to Stroke Incidence in a Japanese Population - Takashima Stroke Registry, Japan, 1988-2010

BACKGROUND

Using a population-based stroke registry system, we evaluated the relationship between ambient temperature parameters and stroke incidence in a Japanese population.

METHODS AND RESULTS

We analyzed data from the Takashima Stroke Registry, which records all stroke occurrences in Takashima City, Japan. The study period of 8,401 days was divided into quintiles of daily weather parameters, and the middle quintile was used as the reference category. Incidence rates (IR per 100,000 person-years) were calculated across the quintiles. Poisson regression analysis was used to calculate the effect of temperature parameters on stroke incidence. There were 2,405 first-ever strokes (1,294 men), including 1,625 ischemic, 545 cerebral hemorrhages, 213 subarachnoid hemorrhages, and 22 unclassified strokes. The stroke IR was higher in the middle quintile of average temperature, 357.3 (328.4-388.8), and for other parameters. After adjustment for age and sex, for all stroke, the incidence rate ratio (IRR) in the highest (Q5: IRR 0.81, 95% confidence interval (CI) 0.71-0.92) and the second-highest (Q4: IRR 0.80, 95% CI 0.71-0.91) quintile was lower than that in the middle quintile (Q3: Reference). Analogous results were observed for the minimum, maximum, and lag-days temperatures, also in the subtypes and across ≥65 years of age, also in females.

CONCLUSIONS

Higher temperatures, irrespective of the parameter (average, minimum, or maximum), had a protective effect against stroke occurrence in Japan.

The role of absolute humidity in respiratory mortality in Guangzhou, a hot and wet city of South China

Background

For the reason that many studies have been inconclusive on the effect of humidity on respiratory disease, we examined the association between absolute humidity and respiratory disease mortality and quantified the mortality burden due to non-optimal absolute humidity in Guangzhou, China.

Methods

Daily respiratory disease mortality including total 42,440 deaths from 1 February 2013 to 31 December 2018 and meteorological data of the same period in Guangzhou City were collected. The distributed lag non-linear model was used to determine the optimal absolute humidity of death and discuss their non-linear lagged effects. Attributable fraction and population attributable mortality were calculated based on the optimal absolute humidity, defined as the minimum mortality absolute humidity.

Results

The association between absolute humidity and total respiratory disease mortality showed an M-shaped non-linear curve. In total, 21.57% (95% CI 14.20 ~ 27.75%) of respiratory disease mortality (9154 deaths) was attributable to non-optimum absolute humidity. The attributable fractions due to high absolute humidity were 13.49% (95% CI 9.56 ~ 16.98%), while mortality burden of low absolute humidity were 8.08% (95% CI 0.89 ~ 13.93%), respectively. Extreme dry and moist absolute humidity accounted for total respiratory disease mortality fraction of 0.87% (95% CI − 0.09 ~ 1.58%) and 0.91% (95% CI 0.25 ~ 1.39%), respectively. There was no significant gender and age difference in the burden of attributable risk due to absolute humidity.

Conclusions

Our study showed that both high and low absolute humidity are responsible for considerable respiratory disease mortality burden, the component attributed to the high absolute humidity effect is greater. Our results may have important implications for the development of public health measures to reduce respiratory disease mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12199-021-01030-3.

Global warming and neurological practice: systematic review

Background

Climate change, including global warming, will cause poorer global health and rising numbers of environmental refugees. As neurological disorders account for a major share of morbidity and mortality worldwide, global warming is also destined to alter neurological practice; however, to what extent and by which mechanisms is unknown. We aimed to collect information about the effects of ambient temperatures and human migration on the epidemiology and clinical manifestations of neurological disorders.

Methods

We searched PubMed and Scopus from 01/2000 to 12/2020 for human studies addressing the influence of ambient temperatures and human migration on Alzheimer’s and non-Alzheimer’s dementia, epilepsy, headache/migraine, multiple sclerosis, Parkinson’s disease, stroke, and tick-borne encephalitis (a model disease for neuroinfections). The protocol was pre-registered with PROSPERO (2020 CRD42020147543).

Results

Ninety-three studies met inclusion criteria, 84 of which reported on ambient temperatures and nine on migration. Overall, most temperature studies suggested a relationship between increasing temperatures and higher mortality and/or morbidity, whereas results were more ambiguous for migration studies. However, we were unable to identify a single adequately designed study addressing how global warming and human migration will change neurological practice. Still, extracted data indicated multiple ways by which these aspects might alter neurological morbidity and mortality soon.

Conclusion

Significant heterogeneity exists across studies with respect to methodology, outcome measures, confounders and study design, including lack of data from low-income countries, but the evidence so far suggests that climate change will affect the practice of all major neurological disorders in the near future. Adequately designed studies to address this issue are urgently needed, requiring concerted efforts from the entire neurological community.

The effects of heatwaves and cold spells on patients admitted with acute ischemic stroke

Background

This study aimed to explore the effects of heatwaves and cold spells on blood pressure, thrombus formation, and systemic inflammation at admission in patients with ischemic stroke.

Methods

Data of patients with ischemic stroke who were admitted to the Second Hospital of Tianjin Medical University between May 2014 and March 2019 were reviewed, along with meteorological data from the same time period. A total of 806 clinically confirmed patients with ischemic stroke (34–97 years old) were included in the final analysis. Heatwaves and cold spells were defined as ≥2 consecutive days with average temperature >95^th percentile (May–August) and <5^th percentile (November–March), respectively. Coagulation parameters, inflammation indices, blood pressure, and neurological impairment were evaluated within 24 hours of admission. General linear and logistic regression models were created to investigate the relationships of heatwaves and cold spells with the examination results of patients with ischemic stroke at admission.

Results

After adjustment for potential environmental confounders, heatwaves were positively associated with high systolic blood pressure (SBP) (β=8.693, P=0.019), diastolic blood pressure (DBP) (β=3.665, P=0.040), reduced thrombin time (TT) (β=−0.642, P=0.027), and activated partial thromboplastin time (APTT) (β=−1.572, P=0.027) in ischemic stroke patients at admission. Cold spells were positively associated with high SBP (β=5.277, P=0.028), DBP (β=4.672, P=0.012), fibrinogen (β=0.315, P=0.011), globulin (β=1.523, P=0.011), and reduced TT (β=−0.784, P<0.001) and APTT (β=−1.062, P=0.024). Cold spells were also associated with a higher risk of respiratory infection [odds ratio (OR) =2.677, P=0.001].

Conclusions

Exposure to heatwaves or cold spells was associated with blood pressure and coagulation at admission in patients with ischemic stroke. Cold spells also resulted in higher levels of inflammation. These findings suggest that changes in coagulation, blood pressure, and inflammation may be the potential biological mechanisms underlying the cerebrovascular effects of exposure to extreme temperatures.

Preliminary development of a prediction model for daily stroke occurrences based on meteorological and calendar information using deep learning framework (Prediction One; Sony Network Communications Inc., Japan)

BACKGROUND

Chronologically meteorological and calendar factors were risks of stroke occurrence. However, the prediction of stroke occurrences is difficult depending on only meteorological and calendar factors. We tried to make prediction models for stroke occurrences using deep learning (DL) software, Prediction One (Sony Network Communications Inc., Tokyo, Japan), with those variables.

METHODS

We retrospectively investigated the daily stroke occurrences between 2017 and 2019. We used Prediction One software to make the prediction models for daily stroke occurrences (present or absent) using 221 chronologically meteorological and calendar factors. We made a prediction models from the 3-year dataset and evaluated their accuracies using the internal cross-validation. Areas under the curves (AUCs) of receiver operating characteristic curves were used as accuracies.

RESULTS

The 371 cerebral infarction (CI), 184 intracerebral hemorrhage (ICH), and 53 subarachnoid hemorrhage patients were included in the study. The AUCs of the several DL-based prediction models for all stroke occurrences were 0.532-0.757. Those for CI were 0.600-0.782. Those for ICH were 0.714-0.988.

CONCLUSION

Our preliminary results suggested a probability of the DL-based prediction models for stroke occurrence only by meteorological and calendar factors. In the future, by synchronizing a variety of medical information among the electronic medical records and personal smartphones as well as integrating the physical activities or meteorological conditions in real time, the prediction of stroke occurrence could be performed with high accuracy, to save medical resources, to have patients care for themselves, and to perform efficient medicine.

Effect of ambient temperature on stroke onset: a time-series analysis between 2003 and 2014 in Shenzhen, China

OBJECTIVE

Evidence on the relationship between ambient temperature and morbidity of different stroke subtypes in China is limited. This study aimed to assess the influence of ambient temperature on stroke risk in Shenzhen, China.

METHODS

From 1 January 2003 to 31 December 2014, 114 552 stroke cases in Shenzhen were collected. A generalised additive model with quasi-Poisson regression combined with a distributed lag non-linear model was applied to evaluate the temperature effects on stroke subtypes. Furthermore, this study explored the variability of the effects across sex, age and education.

RESULTS

The immediate heat effects on ischaemic stroke (IS) and the persistent effects of ambient temperature on intracerebral haemorrhage (ICH) were significant. Overall, the cold-related relative risks (RRs) of IS, ICH and subarachnoid haemorrhage (SAH) were 1.02 (0.97-1.07), 1.16 (1.04-1.30) and 1.12 (0.61-2.04), whereas the heat-related RRs were 1.00 (0.97-1.04), 0.80 (0.73-0.88) and 1.05 (0.63-1.78), respectively. For IS, a weakly beneficial cold effect was found among men while a detrimental heat effect among both men and women, the elderly and higher-educated population at lag0. However, regarding ICH, the temperature effects in men, the young and higher-educated population are stronger at lag0-4, lag0-7 as cold reveals threat and heat reveals protection.

CONCLUSION

Responses of diverse stroke subtypes to ambient temperature varied. Effective measures should be taken to increase public awareness about the effects of ambient temperature on stroke attack and to educate the public about self-protection.

A time series analysis of the relationship between ambient temperature and ischaemic stroke in the Ljubljana area: immediate, delayed and cumulative effects

BACKGROUND

Stroke is a major health problem around the world. Several studies have examine the influence of ambient temperature on incidence of stoke, but they reported different results for different types of stroke and different geographical regions. Hence, effect of ambient temperature is still much of interest, when focusing on ischemic stroke (IS) in regions that have not been examined yet. The aim of our study is to analyse association between IS incidences and short, delayed and cumulative effect of average daily ambient temperature, humidity and pressure in central Europe. To the best of our knowledge, this is the first IS study conducted between 45° and 50° latitude where large part of Central European population resides.

METHODS

We linked daily hospitals' admission data for whole population and separately for two specific age groups with ambient temperature data. We considered patients coming from Ljubljana basin and its immediate surrounding. Data were gathered daily from January 2012 to December 2017. To measure the effect of average ambient temperature, humidity and pressure we used generalized linear model with a log-link-function and a Poisson distribution.

RESULTS

The results of our study show a statistically significant immediate, delayed and cumulative effects of ambient temperatures on IS incidence for the whole population and the population older than 65 years. Specifically, 1 °C reduction in ambient temperature on a given day (Lag 0) increases the IS risk for approximately 5‰ (all population) or 6‰ (population older than 65 years). Similar effects were found for lags from 1 to 6. Analysis of time windows from 0 to 1 days up to 0-28 days also show statistically significant cumulative effect for the same two age groups. IS incidence was not found to be significantly related to pressure or humidity in any group.

CONCLUSION

The findings of this study may help healthcare authorities in central Europe improve existing stroke prevention measures and raise public awareness.

Association between stroke occurrence and changes in atmospheric circulation

Background

The impact of weather on morbidity from stroke has been analysed in previous studies. As the risk of stroke was mostly associated with changing weather, the changes in the daily stroke occurrence may be associated with changes in atmospheric circulation. The aim of our study was to detect and evaluate the association between daily numbers of ischaemic strokes (ISs) and haemorrhagic strokes (HSs) and the teleconnection pattern.

Methods

The study was performed in Kaunas, Lithuania, from 2000 to 2010. The daily numbers of ISs, subarachnoid haemorrhages (SAHs), and intracerebral haemorrhages (ICHs) were obtained from the Kaunas Stroke Register. We evaluated the association between these types of stroke and the teleconnection pattern by applying Poisson regression and adjusting for the linear trend, month, and other weather variables.

Results

During the study period, we analysed 4038 cases (2226 men and 1812 women) of stroke. Of these, 3245 (80.4%) cases were ISs, 533 (13.2%) cases were ICHs, and 260 (6.4%) cases were SAHs. An increased risk of SAH was associated with a change in mean daily atmospheric pressure over 3.9 hPa (RR = 1.49, 95% CI 1.14–1.96), and a stronger El Niño event had a protective effect against SAHs (RR = 0.34, 95% CI 0.16–0.69). The risk of HS was positively associated with East Atlantic/West Russia indices (RR = 1.13, 95% CI 1.04–1.23). The risk of IS was negatively associated with the Arctic Oscillation index on the same day and on the previous day (RR = 0.97, p < 0.033). During November–March, the risk of HS was associated with a positive North Atlantic Oscillation (NAO) (RR = 1.29, 95% CI 1.03–1.62), and the risk of IS was negatively associated with the NAO index (RR = 0.92, 95% CI 0.85–0.99).

Conclusions

The results of our study provide new evidence that the North Atlantic Oscillation, Arctic Oscillation, East Atlantic/West Russia, and El Niño-Southern Oscillation pattern may affect the risk of stroke. The impact of these teleconnections is not identical for various types of stroke. Emergency services should be aware that specific weather conditions are more likely to prompt calls for more severe strokes.

The effect of air-pollution and weather exposure on mortality and hospital admission and implications for further research: A systematic scoping review

BACKGROUND

Air-pollution and weather exposure beyond certain thresholds have serious effects on public health. Yet, there is lack of information on wider aspects including the role of some effect modifiers and the interaction between air-pollution and weather. This article aims at a comprehensive review and narrative summary of literature on the association of air-pollution and weather with mortality and hospital admissions; and to highlight literature gaps that require further research.

METHODS

We conducted a scoping literature review. The search on two databases (PubMed and Web-of-Science) from 2012 to 2020 using three conceptual categories of "environmental factors", "health outcomes", and "Geographical region" revealed a total of 951 records. The narrative synthesis included all original studies with time-series, cohort, or case cross-over design; with ambient air-pollution and/or weather exposure; and mortality and/or hospital admission outcomes.

RESULTS

The final review included 112 articles from which 70 involved mortality, 30 hospital admission, and 12 studies included both outcomes. Air-pollution was shown to act consistently as risk factor for all-causes, cardiovascular, respiratory, cerebrovascular and cancer mortality and hospital admissions. Hot and cold temperature was a risk factor for wide range of cardiovascular, respiratory, and psychiatric illness; yet, in few studies, the increase in temperature reduced the risk of hospital admissions for pulmonary embolism, angina pectoris, chest, and ischemic heart diseases. The role of effect modification in the included studies was investigated in terms of gender, age, and season but not in terms of ethnicity.

CONCLUSION

Air-pollution and weather exposure beyond certain thresholds affect human health negatively. Effect modification of important socio-demographics such as ethnicity and the interaction between air-pollution and weather is often missed in the literature. Our findings highlight the need of further research in the area of health behaviour and mortality in relation to air-pollution and weather, to guide effective environmental health precautionary measures planning.

Impact of COVID-19 on Stroke Caseload in a Major Hyperacute Stroke Unit

Northwick Park Hospital in London, United Kingdom (UK) is one of the busiest stroke units in the country and is located in one of the areas most heavily affected by the COVID-19 pandemic in the first half of 2020. Admissions to the stroke unit and changes during the peak of COVID-19 were reviewed. Compared with the previous year, mean 96 patients were admitted with suspected stroke during April and May 2020 compared with mean 116 per month in non-COVID periods, ratio 0.82, P = 0.01. This reduction involved both strokes and mimics and was unlikely to have occurred by chance. Numbers of patients thrombolysed and of patients referred for thrombectomy decreased dramatically during this time. Mechanisms by which the COVID-19 pandemic and the March lockdown may have affected admissions to the unit are discussed. Reduced admissions to the stroke unit allowed it to contribute its resources to the care of patients with COVID-19 during the peak of admissions.

Association between extreme precipitation and ischemic stroke in Hefei, China: Hospitalization risk and disease burden

BACKGROUND

Ischemic stroke is an acute cardiovascular disease with high disability and mortality. Extreme precipitation has been reported to increase the risk of some cardiovascular diseases and further increase the burden of disease. At present, no studies have evaluated the relationship between extreme precipitation and ischemic stroke.

OBJECTIVE

The aim of this study was to quantitatively analyze the association between extreme precipitation and ischemic stroke hospitalizations and further explore disease burden and its associated susceptible population.

METHODS

In this study, we used Poisson generalized linear model combined with distributed lag nonlinear model to investigate the relationship between extreme precipitation (≥95th percentile) and ischemic stroke and further explored the lag effect of extreme precipitation for population with different individual characteristics.

RESULTS

Ischemic stroke hospitalizations were significantly associated with extreme precipitation. The single-day effect occurred on lag 3 (RR = 1.040, 95% CI: 1.058-1.073) lasted until lag 8 (RR = 1.036, 95% CI: 1.004-1.068). The cumulative lag effects of extreme precipitation on ischemic stroke lasted six days (lag 6-lag 11). Male and people aged ≥65 years were more sensitive to extreme precipitation. The attributable fraction (AF) and numbers (AN) of extreme precipitation on hospitalizations for ischemic stroke were 1.38% and 236.4, respectively.

CONCLUSION

Our study suggested that extreme precipitation may increase the risk of hospital admissions for ischemic stroke, emphasizing the need for society and families to pay more attention to male and people aged ≥65 years.

Population's health information-seeking behaviors and geographic variations of stroke in Malaysia: an ecological correlation and time series study

Stroke has emerged as a major public health concern in Malaysia. We aimed to determine the trends and temporal associations of real-time health information-seeking behaviors (HISB) and stroke incidences in Malaysia. We conducted a countrywide ecological correlation and time series study using novel internet multi-timeline data stream of 6,282 hit searches and conventional surveillance data of 14,396 stroke cases. We searched popular search terms related to stroke in Google Trends between January 2004 and March 2019. We explored trends by comparing average relative search volumes (RSVs) by month and weather through linear regression bootstrapping methods. Geographical variations between regions and states were determined through spatial analytics. Ecological correlation analysis between RSVs and stroke incidences was determined via Pearson's correlations. Forecasted model was yielded through exponential smoothing. HISB showed both cyclical and seasonal patterns. Average RSV was significantly higher during Northeast Monsoon when compared to Southwest Monsoon (P < 0.001). "Red alerts" were found in specific regions and states. Significant correlations existed within stroke related queries and actual stroke cases. Forecasted model showed that as HISB continue to rise, stroke incidence may decrease or reach a plateau. The results have provided valuable insights for immediate public health policy interventions.

The effects of weather on daily emergency ambulance service demand in Taipei: a comparison with Hong Kong

Numerous studies have examined the effects of weather on emergency ambulance service (EAS) demand. Given Taipei's unique physical and social environments, empirical evidence collected from other regions may not be applicable. Collecting more information about the characteristics of vulnerable groups and the effects of weather could help the EAS managing authority in formulating cost-effective EAS policies. This study aims to look at the effects of weather on EAS demand in Taipei and to make a comparison with Hong Kong, which is also an Asian city and has a similar cultural context. The study analyzed over 370,000 EAS usage records from the Taipei City Fire Department. These records were aggregated into time series data according to patients' characteristics and then regressed on meteorological data via multivariate forward regression. The effect size differences of the variance explained by different groups of EAS users' regression models were compared. Afterward, the results of the regression analysis from Taipei were compared with those from a Hong Kong study. Elderly and critical patients in both cities showed significantly more sensitivity to weather than other patients. Further analysis showed that non-trauma cases were related to weather in Taipei. Although both cities had similar results, the Taipei study clearly showed that elderly and critical patients were more sensitive to weather than other patient subgroups. Health education programs should focus on the vulnerable groups identified in this study in order to increase their awareness and help them protect themselves before the onset of adverse weather conditions. By generating results that are directly applicable to Taipei, the formulation of inappropriate EAS policies can be prevented.

Meteorological Variation Is a Predisposing Factor for Aneurismal Subarachnoid Hemorrhage: A 5-Year Multicenter Study in Fuzhou, China

OBJECTIVE

The climatic characteristics of aneurysmal subarachnoid hemorrhage (aSAH) have been reported, but consensus has not yet been reached. It is of great significance to elucidate the relationships between meteorological variation and aSAH in regions with specific climate patterns. We analyzed the occurrence of aSAH in the capital city of Fujian Province, China, through a multicenter, 5-year study, and aimed to reveal the meteorological influences on aSAH in the coastal city of eastern Fujian under the subtropical marine monsoon condition.

METHODS

A total of 2555 consecutive patients with aSAH in Fuzhou were collected using specialized stroke admission database from January 2013 to December 2017. Meteorological parameters including temperature, atmospheric pressure, and humidity were obtained from China Surface Meteorological Station during the same period. Poisson regression was used to explore the association between meteorological parameters and aSAH to calculate the incidence rate ratios (IRRs) with corresponding 95% confidence intervals (CIs). Generalized additive model analysis further revealed the nonlinear relationships between weather and aSAH.

RESULTS

Daily minimum temperature (IRR 0.976, 95% CI 0.958-0.996) and maximum pressure (IRR 1.022, 95% CI 1.001-1.042) were independently correlated with the onset of aSAH. Low temperature (below 16°C) and excessive atmospheric pressure (above 1008 hPa) increased the risk of aSAH. In addition, March in spring and December in winter were the 2 ictus peaks in Fuzhou throughout the year.

CONCLUSIONS

Cold and excessive atmospheric pressure are triggers for the occurrence of aSAH; March in spring and December in winter are the predominant onset periods in Fuzhou.

Health impact of climate change in cities of middle-income countries: the case of China

BACKGROUND

This review examines the human health impact of climate change in China. Through reviewing available research findings under four major climate change phenomena, namely extreme temperature, altered rainfall pattern, rise of sea level and extreme weather events, relevant implications for other middle-income population with similar contexts will be synthesized.

SOURCES OF DATA

Sources of data included bilingual peer-reviewed articles published between 2000 and 2018 in PubMed, Google Scholar and China Academic Journals Full-text Database.

AREAS OF AGREEMENT

The impact of temperature on mortality outcomes was the most extensively studied, with the strongest cause-specific mortality risks between temperature and cardiovascular and respiratory mortality. The geographical focuses of the studies indicated variations in health risks and impacts of different climate change phenomena across the country.

AREAS OF CONTROVERSY

While rainfall-related studies predominantly focus on its impact on infectious and vector-borne diseases, consistent associations were not often found.

GROWING POINTS

Mental health outcomes of climate change had been gaining increasing attention, particularly in the context of extreme weather events. The number of projection studies on the long-term impact had been growing.

AREAS TIMELY FOR DEVELOPING RESEARCH

The lack of studies on the health implications of rising sea levels and on comorbidity and injury outcomes warrants immediate attention. Evidence is needed to understand health impacts on vulnerable populations living in growing urbanized cities and urban enclaves, in particular migrant workers. Location-specific climate-health outcome thresholds (such as temperature-mortality threshold) will be needed to support evidence-based clinical management plans and health impact mitigation strategies to protect vulnerable communities.

Assessing spatial variability of extreme hot weather conditions in Hong Kong: A land use regression approach

The number of extreme hot weather events have considerably increased in Hong Kong in the recent decades. The complex urban context of Hong Kong leads to a significant intra-urban spatial variability in climate. Under such circumstance, a spatial understanding of extreme hot weather condition is urgently needed for heat risk prevention and public health actions. In this study, the extreme hot weather events of Hong Kong were quantified and measured using two indicators - very hot day hours (VHDHs) and hot night hours (HNHs) which were counted based on the summertime hourly-resolved air temperature data from a total of 40 weather stations (WSs) from 2011 to 2015. Using the VHDHs and HNHs at the locations of the 40 WSs as the outcome variables, land use regression (LUR) models are developed to achieve a spatial understanding of the extreme hot weather conditions in Hong Kong. Land surface morphology was quantified as the predictor variables in LUR modelling. A total of 167 predictor variables were considered in the model development process based on a stepwise multiple linear regression (MLR). The performance of resultant LUR models was evaluated via cross validation. VHDHs and HNHs were mapped at the community level for Hong Kong. The mapping results illustrate a significant spatial variation in the extreme hot weather conditions of Hong Kong in both the daytime and nighttime, which indicates that the spatial variation of land use configurations must be considered in the risk assessment and corresponding public health management associated with the extreme hot weather.

Seasonal variation in the occurrence of ischemic stroke: A meta-analysis

Stroke was demonstrated to correlate with seasonal variation. However, the relevant studies were incongruous. To better understand the rules of seasonal impact on ischemic stroke (IS) patients, we performed this meta-analysis. We systematically searched relevant observational studies in Pubmed, Web of science and Embase from January 1, 1980, to November 1, 2017, in English. Patients included in this study were adults who suffered from IS. Stata version 12.0 software was used to pool useful data and calculate incidence rate ratios (IRRs) and their 95% confidence intervals (CIs). We also performed heterogeneity and sensitivity analyses and evaluated publication bias. Thirty-three observational studies involving 234,196 participants were incorporated into the meta-analysis. Summer and December were regarded as reference, respectively. The IRRs were calculated showing: IRR_Winter 1.05 (95% CI 1.04-1.07), IRR_Autumn 1.03 (95% CI 1.02-1.04), IRR_Spring 1.02 (95% CI 1.01-1.03). No obvious difference existed among 12 months. Stratified analyses on Köppen classification were also conducted. Between-study heterogeneity was discovered; however, predefined stratified analyses and meta-regression could not reduce this heterogeneity. Our meta-analysis has revealed very little seasonal variation in the overall study. Both cold and hot months may be high risky for IS after stratified by Köppen Climate Classification. Thus, a rationale to environmental setting of risky patient management could be provided. More studies with specific assessments are warranted for further comprehensive investigation.

The effect characteristics of temperature on stroke mortality in Inner Mongolia and globally

The current study investigated the correlation between stroke mortality and temperature. Monthly and seasonal variations in stroke mortality were plotted and daily stroke-related deaths were calculated. The lag times were calculated using the time series analysis. The correlation between stroke incidence and the diurnal temperature range (DTR) was analyzed using case-crossover analysis. Global stroke mortality was described in five latitudes. In the eastern region of Inner Mongolia, the stroke mortality was 174.18/105, about twice of that of the midwestern regions (87.07/105), and temperature was negatively correlated with stroke mortality. Mortality peaked in the winter and troughed in the summer (χ² = 13.634, P < 0.001). The days in which stroke-related deaths were greater than ten occurred between late October and early April. The effect of temperature on stroke incidence occurred during a lag time of 1 (P = 0.024) or 2 months (P = 0.039). A DTR over 13 °C was positively correlated (r = 0.95, P = 0.004) with stroke with a lag time of 1 day. The effect of temperature on stroke was shown to be the same for various populations. As the latitude increases, stroke mortality also increases with latitudes > 40°; the highest mortality was 188.05/105 at the highest latitude. Only in relatively cold regions as the temperature decreases does stroke mortality increase for various populations. Differences in the time lag as well as in the DTR lag and DTR critical point vary for both the temperature and region.

The added effects of heatwaves on cause-specific mortality: A nationwide analysis in 272 Chinese cities

BACKGROUND

The evidence was limited and inconclusive about the added effects of heatwaves, especially in developing countries.

OBJECTIVE

To evaluate the added effects of heatwaves on cause-specific mortality in China.

METHODS

We designed a nationwide time-series analysis based on daily data from 272 main Chinese cities to from 2013 to 2015. We adopted 12 definitions by combining 4 heat thresholds (90th, 92.5th, 95th, 97.5th percentile of city-specific daily mean temperature) and duration of ≥2, 3 and 4 days. We applied overdispersed generalized additive models with distributed lag models to estimate the city-specific cumulative effects of heatwaves over lags of 0-10 days after controlling for daily temperature. We then, used a meta-regression model to pool the effect estimates at national and regional levels.

RESULTS

Heatwaves could significantly increase risk for mortality from total and cardiopulmonary diseases, including coronary heart disease, ischemic stroke (rather than hemorrhagic stroke) and chronic obstructive pulmonary disease. The effects increased with higher thresholds, but were not appreciably influenced by the duration of heat. The risks generally occurred immediately and lasted for 3 to 5 days. The risks were much larger in the temperate continental zone and the temperate monsoon zones than in the subtropical monsoon zone where there was an evident mortality displacement. The elderly, females and less-educated people were more vulnerable.

CONCLUSIONS

This analysis provided ample evidence for the added mortality risk associated with heatwaves, which had important implications for designing heatwave-warning systems and predicting the disease burden of future heatwaves.

Mean air temperature as a risk factor for stroke mortality in São Paulo, Brazil

In Brazil, chronic diseases account for the largest percentage of all deaths among men and women. Among the cardiovascular diseases, stroke is the leading cause of death, accounting for 10% of all deaths. We evaluated associations between stroke and mean air temperature using recorded mortality data and meteorological station data from 2002 to 2011. A time series analysis was applied to 55,633 mortality cases. Ischemic and hemorrhagic strokes (IS and HS, respectively) were divided to test different impact on which subgroup. Poisson regression with distributed lag non-linear model was used and adjusted for seasonality, pollutants, humidity, and days of the week. HS mortality was associated with low mean temperatures for men relative risk (RR) = 2.43 (95% CI, 1.12-5.28) and women RR = 1.39 (95% CI, 1.03-1.86). RR of IS mortality was not significant using a 21-day lag window. Analyzing the lag response separately, we observed that the effect of temperature is acute in stroke mortality (higher risk among lags 0-5). However, for IS, higher mean temperatures were significant for this subtype with more than 15-day lag. Our findings showed that mean air temperature is associated with stroke mortality in the city of São Paulo for men and women and IS and HS may have different triggers. Further studies are needed to evaluate physiologic differences between these two subtypes of stroke.

The role of weather conditions and normal level of air pollution in appearance of stroke in the region of Southeast Europe

We investigated correlation between the normal level of air pollution, weather conditions and stroke occurrence in the region of Southeast Europe with a humid continental climate. This retrospective study included 1963 patients, 1712 (87.2%) with ischemic (IS) and 251 (12.8%) with hemorrhagic stroke (HS) admitted to emergency department. The number of patients, values of weather condition (meteorological parameters) [air temperature (°C), atmospheric pressure (kPa), relative humidity (%)] and concentrations of air pollutants [particulate matter (PM₁₀), nitrogen dioxide (NO₂), ozone (O₃)], were recorded and evaluated for each season (spring, summer, autumn, winter) during 2 years (July 2008-June 2010). The highest rate of IS was observed during spring (28.9%) (p = 0.0002) and HS in winter (33.9%) (p = 0.0006). We have found negative Spearman's correlations (after Bonferroni adjustment for the multiple correlations) of the number of males with values of relative humidity (%) (day 0, rho = - 0.15), the total number of strokes (day 2, rho = - 0.12), females (day 2, rho = - 0.12) and IS (day 2, rho = - 0.13) with concentrations of PM₁₀ (µg/m³), as well as negative correlations of the number of females (day 2, rho = - 0.12) and IS (day 2, rho = - 0.12) with concentrations of NO₂ (µg/m³) (for all p < 0.002). In winter, the number of HS (day 0, rho = 0.25, p = 0.001) positively correlated with concentrations of O₃ (µg/m³). The appearance of stroke has seasonal variations, with the highest rates during spring and winter. Positive correlation between the number of HS and values of O₃ requires an additional reduction of the legally permitted pollutants concentrations.

Association between Ambient Temperatures and Mental Disorder Hospitalizations in a Subtropical City: A Time-Series Study of Hong Kong Special Administrative Region

Background: Mental disorders have been found to be positively associated with temperature in cool to cold climatic regions but the association in warmer regions is unclear. This study presented the short-term association between temperatures and mental disorder hospitalizations in a subtropical city with a mean annual temperature over 21 °C. Methods: Using Poisson-generalized additive models and distributed-lagged nonlinear models, daily mental disorder hospitalizations between 2002 and 2011 in Hong Kong were regressed on daily mean temperature, relative humidity, and air pollutants, adjusted for seasonal trend, long-term trend, day-of-week, and holiday. Analyses were stratified by disease class, gender and age-group. Results: 44,600 admissions were included in the analysis. Temperature was positively associated with overall mental-disorder hospitalizations (cumulative relative risk at 28 °C vs. 19.4 °C (interquartile range, lag 0-2 days) = 1.09 (95% confidence interval 1.03, 1.15)), with the strongest effect among the elderly (≥75 years old). Transient mental disorders due to conditions classified elsewhere and episodic mood disorders also showed strong positive associations with temperature. Conclusion: This study found a positive temperature-mental-disorder admissions association in a warm subtropical region and the association was most prominent among older people. With the dual effect of global warming and an aging population, targeted strategies should be designed to lower the disease burden.

Relationship of Meteorological and Air Pollution Parameters with Pneumonia in Elderly Patients

Background and Purpose

In this study, we aimed to evaluate the relationship between pneumonia and meteorological parameters (temperature, humidity, precipitation, airborne particles, sulfur dioxide (SO₂), carbon monoxide (CO), nitrogen dioxide (NO₂), nitrite oxide (NO), and nitric oxide (NOX)) in patients with the diagnosis of pneumonia in the emergency department.

Methods

Our study was performed retrospectively with patients over 65 years of age who were diagnosed with pneumonia. The meteorological variables in the days of diagnosing pneumonia were compared with the meteorological variables in the days without diagnosis of pneumonia. The sociodemographic characteristics, complete blood count of the patients, and meteorological parameters (temperature, humidity, precipitation, airborne particles, SO2, CO, NO2, NO, and NOX) were investigated.

Results

When the temperature was high and low, the number of days consulted due to pneumonia was related to low air temperature (p < 0.05). During the periods when PM 10, NO, NO2, NOX, and CO levels were high, the number of days referred for pneumonia was increased (p < 0.05).

Conclusion

As a result, climatic (temperature, humidity, pressure levels, rain, etc.) and environmental factors (airborne particles, CO, NO, and NOX) were found to be effective in the number of patients admitted to the hospital due to pneumonia.

Seasonal variation of admission severity and outcomes in ischemic stroke - a consecutive hospital-based stroke registry

Different morbidities and mortalities of ischemic stroke may occur among seasons. For detecting the seasonal variations of severity after stroke onset and prognosis, we employed a retrospective analysis on a prospective regional hospital-based stroke registry and included a total of 1039 consecutive patients with onset date from January 2014 to December 2015. Patients were divided into four groups according to the onset seasons. Baseline characteristics, stroke subtypes, admission National Institute of Health Stroke Scale (NIHSS) score and modified Rankin Scale (mRS) score in 90 d were recorded and compared. Ordinal logistic regression was used to evaluate the association of seasons and severity or outcomes. Higher proportion of cardiac embolisms appeared in spring and winter (p < 0.001). The median admission NIHSS score was 5 in spring, 3 in summer, 4 in fall and 4 in winter (p = 0.036). After 90 d from onset, 40.5% of patients in spring suffered poor outcome (mRS 3-6), while 24.6% in summer, 33.9% in fall and 40.1% in winter (p < 0.001). After adjusted for age, sex, stroke subtypes and other covariates, patients in spring and winter had 1.76 times (95%CI 1.14-2.70, p = 0.010) and 1.53 times (95%CI 1.08-2.18, p = 0.017) the risk of suffering higher severity category than patients in summer, respectively. Compared with summer group, risk of worse outcomes at 90 d increased to 2.30 times in spring (95%CI 1.53-3.45, p < 0.001), 1.57 times in fall (95%CI 1.14-2.16, p = 0.006) and 2.09 times in winter (95%CI 1.50-2.91, p < 0.001), respectively. In conclusion, onset seasons were associated with severity and outcomes in ischemic stroke, and patients admitted in spring and winter had more severity and worse outcomes than patients in summer.

Environmental Risk Factors for Stroke and Cardiovascular Disease

Besides the classical individual stroke risk factors a new class has appeared, the environmental risk factors. After a review of the evidences demonstrating that air pollution is a potent risk factor (Part 1), we propose an update of other physical, chemical, and biological factors, now considered as risk factors (Part 2). One of the challenges is to precise their specific roles as they can be combined in their noxious impacts (traffic air pollution + noise + weather + infections). This knowledge has practical consequences; From now on, medical advices cannot be limited to individual recommendations but must also deal with environmental public health issues.

The cold effect of ambient temperature on ischemic and hemorrhagic stroke hospital admissions: A large database study in Beijing, China between years 2013 and 2014-Utilizing a distributed lag non-linear analysis

The effects of ambient temperature on stroke death in China have been well addressed. However, few studies are focused on the attributable burden for the incident of different types of stroke due to ambient temperature, especially in Beijing, China. We purpose to assess the influence of ambient temperature on hospital stroke admissions in Beijing, China. Data on daily temperature, air pollution, and relative humidity measurements and stroke admissions in Beijing were obtained between 2013 and 2014. Distributed lag non-linear model was employed to determine the association between daily ambient temperature and stroke admissions. Relative risk (RR) with 95% confidence interval (CI) and Attribution fraction (AF) with 95% CI were calculated based on stroke subtype, gender and age group. A total number of 147, 624 stroke admitted cases (including hemorrhagic and ischemic types of stroke) were documented. A non-linear acute effect of cold temperature on ischemic and hemorrhagic stroke hospital admissions was evaluated. Compared with the 25th percentile of temperature (1.2 °C), the cumulative RR of extreme cold temperature (first percentile of temperature, -9.6 °C) was 1.51 (95% CI: 1.08-2.10) over lag 0-14 days for ischemic type and 1.28 (95% CI: 1.03-1.59) for hemorrhagic stroke over lag 0-3 days. Overall, 1.57% (95% CI: 0.06%-2.88%) of ischemic stroke and 1.90% (95% CI: 0.40%-3.41%) of hemorrhagic stroke was attributed to the extreme cold temperature over lag 0-7 days and lag 0-3 days, respectively. The cold temperature's impact on stroke admissions was found to be more obvious in male gender and the youth compared to female gender and the elderly. Exposure to extreme cold temperature is associated with increasing both ischemic and hemorrhagic stroke admissions in Beijing, China.

Heat and mortality for ischemic and hemorrhagic stroke in 12 cities of Jiangsu Province, China

BACKGROUND

Little evidence exists on the relationship between heat and subtypes of stroke mortality, especially in China. Moreover, few studies have reported the effect modification by individual characteristics on heat-related stroke mortality. In this study, we aimed to evaluate the effect of heat exposure on total, ischemic, and hemorrhagic stroke mortality and its individual modifiers in 12 cities in Jiangsu Province, China during 2009 to 2013.

METHODS

We first used a distributed lag non-linear model with quasi-Poisson regression to examine the city-specific heat-related total, ischemic, and hemorrhagic stroke mortality risks at 99th percentile vs. 75th percentile of daily mean temperature in the whole year for each city, while adjusting for long-term trend, season, relative humidity, and day of the week. Then, we used a random-effects meta-analysis to pool the city-specific risk estimates. We also considered confounding by air pollution and effect modification by gender, age, education level, and death location.

RESULTS

Overall, the heat-related mortality risk in 12 Jiangsu cities was 1.54 (95%CI: 1.44 to 1.65) for total stroke, 1.63 (95%CI: 1.48 to 1.80) for ischemic stroke, and 1.36 (95%CI: 1.26 to 1.48) for hemorrhagic stroke, respectively. Estimated total, ischemic, and hemorrhagic stroke mortality risks were higher for women versus men, older people versus younger people, those with low education levels versus high education levels, and deaths that occurred outside of hospital. Air pollutants did not significantly influence the heat-related stroke mortality risk.

CONCLUSIONS

Heat exposure significantly increased both ischemic and hemorrhagic stroke mortality risks in Jiangsu Province, China. Females, the elderly, and those with low education levels are particularly vulnerable to this effect.

The Effects of Various Weather Conditions as a Potential Ischemic Stroke Trigger in Dogs

Stroke is the fifth leading cause of death in the United States, and is the leading cause of serious, long-term disability worldwide. There are at least 795,000 new or recurrent strokes each year, and approximately 85% of all stroke occurrences are ischemic. Unfortunately, companion animals are also at risk for ischemic stroke. Although the exact incidence of ischemic stroke in companion animals is unknown, some studies, and the veterinary information network (VIN), report that approximately 3% of neurological case referrals are due to a stroke. There is a long list of predisposing factors associated with the risk of ischemic stroke in both humans and canines; however, these factors do not explain why a stroke happens at a particular time on a particular day. Our understanding of these potential stroke “triggers” is limited, and the effect of transient environmental exposures may be one such “trigger”. The present study investigated the extent to which the natural occurrence of canine ischemic stroke was related to the weather conditions in the time-period immediately preceding the onset of stroke. The results of the present study demonstrated that the change in weather conditions could be a potential stroke trigger, with the strokes evaluated occurring after periods of rapid, large fluctuations in weather conditions. There are currently no epidemiological data on the seasonal variability of ischemic stroke in dogs, and determining whether canine stroke parallels human stroke would further validate the use of companion dogs as an appropriate naturally occurring model.

Humidity May Modify the Relationship between Temperature and Cardiovascular Mortality in Zhejiang Province, China

Background: The evidence of increased mortality attributable to extreme temperatures is widely characterized in climate-health studies. However, few of these studies have examined the role of humidity on temperature-mortality association. We investigated the joint effect between temperature and humidity on cardiovascular disease (CVD) mortality in Zhejiang Province, China. Methods: We collected data on daily meteorological and CVD mortality from 11 cities in Zhejiang Province during 2010–2013. We first applied time-series Poisson regression analysis within the framework of distributed lag non-linear models to estimate the city-specific effect of temperature and humidity on CVD mortality, after controlling for temporal trends and potential confounding variables. We then applied a multivariate meta-analytical model to pool the effect estimates in the 11 cities to generate an overall provincial estimate. The joint effects between them were calculated by the attributable fraction (AF). The analyses were further stratified by gender, age group, education level, and location of cities. Results: In total, 120,544 CVD deaths were recorded in this study. The mean values of temperature and humidity were 17.6 °C and 72.3%. The joint effect between low temperature and high humidity had the greatest impact on the CVD death burden over a lag of 0–21 days with a significant AF of 31.36% (95% eCI: 14.79–38.41%), while in a condition of low temperature and low humidity with a significant AF of 16.74% (95% eCI: 0.89, 24.44). The AFs were higher at low temperature and high humidity in different subgroups. When considering the levels of humidity, the AFs were significant at low temperature and high humidity for males, youth, those with a low level of education, and coastal area people. Conclusions: The combination of low temperature and high humidity had the greatest impact on the CVD death burden in Zhejiang Province. This evidence has important implications for developing CVD interventions.

Various meteorological conditions exhibit both immediate and delayed influences on the risk of stroke events: The HEWS-stroke study

We hypothesized that meteorological conditions on the onset day and conditions on the former days may play important roles in the modulation of physical conditions. Associations of meteorological factors and their changes in former days with stroke onset are of interest. We conducted a multicenter retrospective study to evaluate the frequency of stroke events and their interaction with meteorological conditions and their daily changes. Acute stroke patients (n = 3935, 73.5±12.4 years, 1610 females) who were admitted to 7 stroke hospitals in three restricted areas were enrolled in this study. Poisson regression models involving time-lag variables was used to compare daily rates of stroke events with mean thermo-hydrological index (THI), atmospheric pressure, and their daily changes. We divided onset days into quintiles based on the THI, atmospheric pressure, and their daily changes for the last 7 days. The frequencies of ischemic stroke significantly increased when THI varied either cooler or warmer from a previous day (extremely cooler, risk ratio (RR) 1.19, 95% confidence interval (CI) 1.05 to 1.34; extremely warmer, RR 1.16, 95% CI 1.03 to 1.31; r2 = 0.001 for the best regression, p = 0.001). Intracerebral hemorrhage frequencies significantly decreased on high-THI days (extremely high, RR 0.72, 95% CI 0.54 to 0.95; r2 = 0.013 for the best regression, p<0.001) and increased in high atmospheric pressure days (high, RR 1.31, 95% CI 1.04 to 1.65; r2 = 0.009 for the best regression, p<0.001). Additionally, even after adjusting for the THI on the onset day and its changes for the other days, intracerebral hemorrhage increased when THI got extremely cooler in 4 days prior (RR 1.33, 95% CI 1.03 to 1.71, r2 = 0.006 for the best regression, p<0.001). Various meteorological conditions may exhibit influences on stroke onset. And, when temperature cooled, there may be a possibility to show delayed influence on the frequency of intracerebral hemorrhage 4 days later.

Impact of ambient temperature on morbidity and mortality: An overview of reviews

The objectives were (i) to conduct an overview of systematic reviews to summarize evidence from and evaluate the methodological quality of systematic reviews assessing the impact of ambient temperature on morbidity and mortality; and (ii) to reanalyse meta-analyses of cold-induced cardiovascular morbidity in different age groups. The registration number is PROSPERO-CRD42016047179. PubMed, Embase, the Cochrane Library, Web of Science, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Global Health were systematically searched to identify systematic reviews. Two reviewers independently selected studies for inclusion, extracted data, and assessed quality. The Assessment of Multiple Systematic Reviews (AMSTAR) checklist was used to assess the methodological quality of included systematic reviews. Estimates of morbidity and mortality risk in association with heat exposure, cold exposure, heatwaves, cold spells and diurnal temperature ranges (DTRs) were the primary outcomes. Twenty-eight systematic reviews were included in the overview of systematic reviews. (i) The median (interquartile range) AMSTAR scores were 7 (1.75) for quantitative reviews and 3.5 (1.75) for qualitative reviews. (ii) Heat exposure was identified to be associated with increased risk of cardiovascular, cerebrovascular and respiratory mortality, but was not found to have an impact on cardiovascular or cerebrovascular morbidity. (iii) Reanalysis of the meta-analyses indicated that cold-induced cardiovascular morbidity increased in youth and middle-age (RR=1.009, 95% CI: 1.004-1.015) as well as the elderly (RR=1.013, 95% CI: 1.007-1.018). (iv) The definitions of temperature exposure adopted by different studies included various temperature indicators and thresholds. In conclusion, heat exposure seemed to have an adverse effect on mortality and cold-induced cardiovascular morbidity increased in the elderly. Developing definitions of temperature exposure at the regional level may contribute to more accurate evaluations of the health effects of temperature.

Time series models of environmental exposures: Good predictions or good understanding

Time series data are popular in environmental epidemiology as they make use of the natural experiment of how changes in exposure over time might impact on disease. Many published time series papers have used parameter-heavy models that fully explained the second order patterns in disease to give residuals that have no short-term autocorrelation or seasonality. This is often achieved by including predictors of past disease counts (autoregression) or seasonal splines with many degrees of freedom. These approaches give great residuals, but add little to our understanding of cause and effect. We argue that modelling approaches should rely more on good epidemiology and less on statistical tests. This includes thinking about causal pathways, making potential confounders explicit, fitting a limited number of models, and not over-fitting at the cost of under-estimating the true association between exposure and disease.

Relationship of meteorological factors and acute stroke events in Kaunas (Lithuania) in 2000-2010

Some researchers have hypothesised that meteorological factors may have an impact on acute cerebrovascular diseases. The aim of this study was to determine an impact of some meteorological factors on occurrence of acute cerebrovascular events in the middle-aged Kaunas population. Kaunas stroke register data were used. Data on meteorological factors for the time period from 2000 to 2010 were obtained from the Lithuanian Hydrometeorological Service Kaunas Meteorological Station. We analysed 4038 cases with stroke. Ischemic strokes composed 80.4% and haemorrhagic strokes-19.6%. According to Poisson regression analysis, significant negative correlation between ischemic, haemorrhagic and all types of stroke and ambient air temperature was found (β coefficient - 0.007, -0.016, -0.009, p < 0.001, respectively). Results of ARIMA showed that ambient temperature of the day of stroke onset was associated with the occurrence of ischemic, haemorrhagic and all types of stroke: when temperature was lower, the risk of stroke was higher (-0.006, -0.003, -0.009, p < 0.001, respectively). Low temperature on the event day and 1 and 2 days before the event was associated with higher incidence of haemorrhagic stroke in women. Low ambient temperature on the event day increased incidence of haemorrhagic stroke in subjects 55-64 years. High wind speed on the event day was associated with higher incidence of ischemic stroke in older subjects. Meteorological factors may have some impact on the risk of acute cerebrovascular events. Health care providers should focus on preventive measures, which can reduce these risks.