Referent selection in case-crossover analyses of acute health effects of air pollution

Comparison of four case-crossover study designs to analyze the association between air pollution exposure and acute myocardial infarction

The case-crossover design is frequently used for analyzing the acute health effects of air pollution. Nevertheless, only a few studies compared different methods for selecting control periods. In this study, the bidirectional method and three time-stratified methods were used to estimate the association between air pollution and acute myocardial infarction (AMI) in Charleroi, Belgium, during 1999-2008. The strongest associations between air pollution and AMI were observed for PM10 and NO(2) during the warm period, OR = 1.095 (95 % CI: 1.003-1.169) and OR = 1.120 (95 % CI: 1.001-1.255), respectively. The results of this study reinforce the evidence of the acute effects of air pollution on AMI, especially during the warm season. This study suggests that the different methods of case-crossover study design are suitable to studying the association between acute events and air pollution. The temperature-stratified design is useful to exclude temperature as a potential confounder.

Short-term effects of particulate matter constituents on daily hospitalizations and mortality in five South-European cities: results from the MED-PARTICLES project

BACKGROUND

Few recent studies examined acute effects on health of individual chemical species in the particulate matter (PM) mixture, and most of them have been conducted in North America. Studies in Southern Europe are scarce. The aim of this study is to examine the relationship between particulate matter constituents and daily hospital admissions and mortality in five cities in Southern Europe.

METHODS

The study included five cities in Southern Europe, three cities in Spain: Barcelona (2003-2010), Madrid (2007-2008) and Huelva (2003-2010); and two cities in Italy: Rome (2005-2007) and Bologna (2011-2013). A case-crossover design was used to link cardiovascular and respiratory hospital admissions and total, cardiovascular and respiratory mortality with a pre-defined list of 16 PM10 and PM2.5 constituents. Lags 0 to 2 were examined. City-specific results were combined by random-effects meta-analysis.

RESULTS

Most of the elements studied, namely EC, SO4(2-), SiO2, Ca, Fe, Zn, Cu, Ti, Mn, V and Ni, showed increased percent changes in cardiovascular and/or respiratory hospitalizations, mainly at lags 0 and 1. The percent increase by one interquartile range (IQR) change ranged from 0.69% to 3.29%. After adjustment for total PM levels, only associations for Mn, Zn and Ni remained significant. For mortality, although positive associations were identified (Fe and Ti for total mortality; EC and Mg for cardiovascular mortality; and NO3(-) for respiratory mortality) the patterns were less clear.

CONCLUSIONS

The associations found in this study reflect that several PM constituents, originating from different sources, may drive previously reported results between PM and hospital admissions in the Mediterranean area.

Short-term effects of fine particulate air pollution on hospital admissions for cardiovascular diseases: a case-crossover study in a tropical city

This study was undertaken to determine whether there was an association between fine particles (PM2.5) levels and hospital admissions for cardiovascular diseases (CVD) in Kaohsiung, Taiwan. Hospital admissions for CVD (including ischemic heart disease [IHD], stroke, congestive heart failure [CHF], and arrhythmias) and ambient air pollution data for Kaohsiung were obtained for the period from 2006-2010. The relative risk of hospital admissions for CVD was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), elevated number of admissions for CVD were significantly associated with higher PM2.5 levels only on cool days (<25°C), with an interquartile range rise associated with a 47% (95% CI = 39-56%), 48% (95% CI = 40-56%), 47% (95% CI = 34-61%), and 51% (95% CI = 34-70%) increase in IHD, stroke, CHF, and arrhythmias admissions, respectively. No significant associations between PM2.5 and hospital admissions for CVD were observed on warm days. In the two-pollutant models, PM2.5 levels remained significant even controlling for sulfur dioxide, nitrogen dioxide, carbon monoxide, or ozone on cool days. This study provides evidence that higher levels of PM2.5 enhance the risk of hospital admissions for CVD in Kaohsiung, Taiwan.

Short-Term Effects of Coarse Particulate Matter on Hospital Admissions for Cardiovascular Diseases: A Case-Crossover Study in a Tropical City

This study was undertaken to determine whether there was an association between coarse particles (PM2.5-10) levels and frequency of hospital admissions for cardiovascular diseases (CVD) in Kaohsiung, Taiwan. Hospital admissions for CVD, including ischemic heart disease (IHD), stroke, congestive heart failure (CHF), and arrhythmias, and ambient air pollution data levels for Kaohsiung were obtained for the period 2006-2010. The relative risk of hospital admissions for CVD was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased rates of admissions for CVD were significantly associated with higher coarse PM levels only on cool days (< 25°C), with a 10-μg/m(3) elevation in PM2.5-10 concentrations associated with a 3% (95% CI = 2-4%) rise in IHD admissions, 5% (95% CI = 4-6%) increase in stroke admissions, 3% (95% CI = 1-6%) elevation in CHF admissions, and 3% (95% CI = 0-6%) rise in arrhythmias admissions. No significant associations were found between coarse particle levels and number of hospital admissions for CVD on warm days. In the two-pollutant models, PM2.5-10 levels remained significantly correlated with higher rate of CVD admissions even controlling for sulfur dioxide, nitrogen dioxide, carbon monoxide, or ozone on cool days. Compared to the effect estimate associated with a 10-μg/m(3) increase in PM2.5 levels, effect estimates of frequency of CVD-related admissions associated with a 10-μg/m(3) rise in coarse PM levels were weaker. This study provides evidence that higher levels of PM2.5-10 enhance the risk of hospital admissions for CVD.

Fine particulate air pollution and outpatient department visits for headache in Taipei, Taiwan

This study was undertaken to determine whether there was an association between fine particle matter (PM(2.5)) levels and daily outpatient department visits (OPD) for headaches in Taipei, Taiwan. Daily OPD visits for headaches and ambient air pollution data for Taipei were obtained for the period 2006-2011. The relative risk of visits for OPD headaches was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased OPD visits for headaches were significantly associated with levels of PM(2.5) both on warm days (>23°C) and cool days (<23°C), with an interquartile range rise associated with a 12% (95% CI = 10-14%) and 3% (95% CI = 1-5%) elevation in OPD visits for headaches, respectively. In the two-pollutant models, PM(2.5) remained significant after inclusion of sulfur dioxide (SO₂) or ozone (O₃) on both warm and cool days. This study provides evidence that higher levels of PM(2.5) increase the risk of OPD visits for headaches in Taipei, Taiwan.

Air pollution and daily clinic visits for migraine in a subtropical city: Taipei, Taiwan

This study was undertaken to determine whether there was an association between air pollutant levels and daily clinic visits for migraine in Taipei, Taiwan. Daily clinic visits for migraine and ambient air pollution data for Taipei were obtained for the period 2006-2011. The relative risk of clinic visits for migraine was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. In the single-pollutant models, on warm days (>23°C) statistically significant positive associations were found for increased rate of migraine occurrence and levels of particulate matter (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3). On cool days (<23°C), all pollutants were significantly associated with increased migraine visits except CO and SO2. For the two-pollutant models, O3 and NO2 were significant for higher rate of migraine visits in combination with each of the other four pollutants on cool days. On warm days, CO remained statistically significant in all two-pollutant models. This study provides evidence that higher levels of ambient air pollutants enhance the risk of clinic visits for migraine.

The association of cold weather and all-cause and cause-specific mortality in the island of Ireland between 1984 and 2007

BACKGROUND

This study aimed to assess the relationship between cold temperature and daily mortality in the Republic of Ireland (ROI) and Northern Ireland (NI), and to explore any differences in the population responses between the two jurisdictions.

METHODS

A time-stratified case-crossover approach was used to examine this relationship in two adult national populations, between 1984 and 2007. Daily mortality risk was examined in association with exposure to daily maximum temperatures on the same day and up to 6 weeks preceding death, during the winter (December-February) and an extended cold period (October-March), using distributed lag models. Model stratification by age and gender assessed for modification of the cold weather-mortality relationship.

RESULTS

In the ROI, the impact of cold weather in winter persisted up to 35 days, with a cumulative mortality increase for all-causes of 6.4% (95% CI = 4.8%-7.9%) in relation to every 1°C drop in daily maximum temperature, similar increases for cardiovascular disease (CVD) and stroke, and twice as much for respiratory causes. In NI, these associations were less pronounced for CVD causes, and overall extended up to 28 days. Effects of cold weather on mortality increased with age in both jurisdictions, and some suggestive gender differences were observed.

CONCLUSIONS

The study findings indicated strong cold weather-mortality associations in the island of Ireland; these effects were less persistent, and for CVD mortality, smaller in NI than in the ROI. Together with suggestive differences in associations by age and gender between the two Irish jurisdictions, the findings suggest potential contribution of underlying societal differences, and require further exploration. The evidence provided here will hope to contribute to the current efforts to modify fuel policy and reduce winter mortality in Ireland.

Conditional Poisson models: a flexible alternative to conditional logistic case cross-over analysis

BACKGROUND

The time stratified case cross-over approach is a popular alternative to conventional time series regression for analysing associations between time series of environmental exposures (air pollution, weather) and counts of health outcomes. These are almost always analyzed using conditional logistic regression on data expanded to case-control (case crossover) format, but this has some limitations. In particular adjusting for overdispersion and auto-correlation in the counts is not possible. It has been established that a Poisson model for counts with stratum indicators gives identical estimates to those from conditional logistic regression and does not have these limitations, but it is little used, probably because of the overheads in estimating many stratum parameters.

METHODS

The conditional Poisson model avoids estimating stratum parameters by conditioning on the total event count in each stratum, thus simplifying the computing and increasing the number of strata for which fitting is feasible compared with the standard unconditional Poisson model. Unlike the conditional logistic model, the conditional Poisson model does not require expanding the data, and can adjust for overdispersion and auto-correlation. It is available in Stata, R, and other packages.

RESULTS

By applying to some real data and using simulations, we demonstrate that conditional Poisson models were simpler to code and shorter to run than are conditional logistic analyses and can be fitted to larger data sets than possible with standard Poisson models. Allowing for overdispersion or autocorrelation was possible with the conditional Poisson model but when not required this model gave identical estimates to those from conditional logistic regression.

CONCLUSIONS

Conditional Poisson regression models provide an alternative to case crossover analysis of stratified time series data with some advantages. The conditional Poisson model can also be used in other contexts in which primary control for confounding is by fine stratification.

Conditional Poisson models: a flexible alternative to conditional logistic case cross-over analysis

BACKGROUND

The time stratified case cross-over approach is a popular alternative to conventional time series regression for analysing associations between time series of environmental exposures (air pollution, weather) and counts of health outcomes. These are almost always analyzed using conditional logistic regression on data expanded to case-control (case crossover) format, but this has some limitations. In particular adjusting for overdispersion and auto-correlation in the counts is not possible. It has been established that a Poisson model for counts with stratum indicators gives identical estimates to those from conditional logistic regression and does not have these limitations, but it is little used, probably because of the overheads in estimating many stratum parameters.

METHODS

The conditional Poisson model avoids estimating stratum parameters by conditioning on the total event count in each stratum, thus simplifying the computing and increasing the number of strata for which fitting is feasible compared with the standard unconditional Poisson model. Unlike the conditional logistic model, the conditional Poisson model does not require expanding the data, and can adjust for overdispersion and auto-correlation. It is available in Stata, R, and other packages.

RESULTS

By applying to some real data and using simulations, we demonstrate that conditional Poisson models were simpler to code and shorter to run than are conditional logistic analyses and can be fitted to larger data sets than possible with standard Poisson models. Allowing for overdispersion or autocorrelation was possible with the conditional Poisson model but when not required this model gave identical estimates to those from conditional logistic regression.

CONCLUSIONS

Conditional Poisson regression models provide an alternative to case crossover analysis of stratified time series data with some advantages. The conditional Poisson model can also be used in other contexts in which primary control for confounding is by fine stratification.

Particulate matter modifies the association between airborne pollen and daily medical consultations for pollinosis in Tokyo

Pollen from Japanese cedar (sugi) and cypress (hinoki) trees is responsible for the growing prevalence of allergic rhinitis, especially pollinosis in Japan. Previous studies have suggested that air pollutants enhance the allergic response to pollen in susceptible individuals. We conducted a time-stratified case-crossover study to examine the potential modifying effects of PM2.5 and suspended particulate matter (SPM) on the association between pollen concentration and daily consultations for pollinosis. A total of 11,713 daily pollinosis cases (International Classification of Diseases, ICD-10, J30.1) from January to May, 2001-2011, were obtained from a clinic in Chiyoda, Tokyo. Daily pollen counts and the daily mean values of air pollutants (PM2.5, SPM, SO2, NO2, CO, and O3) were collected from monitoring stations across Tokyo. The effects of pollen were stratified by the level of PM2.5 and SPM to examine the interaction effect of pollen and particulate pollutants. We found a statistically significant interaction between pollen concentration and PM2.5/SPM. On days with a high level of PM2.5 (>95th percentile), an interquartile increase in the mean cumulative pollen count (an average of 28 pollen grains per cm(2) during lag-days 0 to 5) corresponded to a 10.30% (95%CI: 8.48%-12.16%) increase in daily new pollinosis cases, compared to 8.04% (95%CI: 7.28%-8.81%) on days with a moderate level of PM2.5 (5th-95th percentile). This interaction persisted when different percentile cut-offs were used and was robust to the inclusion of other air pollutants. A similar interaction pattern was observed between SPM and pollen when a less extreme cut-off for SPM was used to stratify the effect of pollen. Our study showed the acute effect of pollen was greater when the concentration of air particulate pollutant, specifically PM2.5 and SPM, was higher. These findings are consistent with the notion that particulate air pollution may act as an adjuvant that promotes allergic disease (i.e. pollinosis).

Effect of atmospheric mixing layer depth variations on urban air quality and daily mortality during Saharan dust outbreaks

Several epidemiological studies have shown that the outbreaks of Saharan dust over southern European countries can cause negative health effects. The reasons for the increased toxicity of airborne particles during dust storms remain to be understood although the presence of biogenic factors carried by dust particles and the interaction between dust and man-made air pollution have been hypothesized as possible causes. Intriguingly, recent findings have also demonstrated that during Saharan dust outbreaks the local man-made particulates can have stronger effects on health than during days without outbreaks. We show that the thinning of the mixing layer (ML) during Saharan dust outbreaks, systematically described here for the first time, can trigger the observed higher toxicity of ambient local air. The mixing layer height (MLH) progressively reduced with increasing intensity of dust outbreaks thus causing a progressive accumulation of anthropogenic pollutants and favouring the formation of new fine particles or specific relevant species likely from condensation of accumulated gaseous precursors on dust particles surface. Overall, statistically significant associations of MLH with all-cause daily mortality were observed. Moreover, as the MLH reduced, the risk of mortality associated with the same concentration of particulate matter increased due to the observed pollutant accumulation. The association of MLH with daily mortality and the effect of ML thinning on particle toxicity exacerbated when Saharan dust outbreaks occurred suggesting a synergic effect of atmospheric pollutants on health which was amplified during dust outbreaks. Moreover, the results may reflect higher toxicity of primary particles which predominate on low MLH days.

Relation of temperature and humidity to the risk of recurrent gout attacks

Gout attack risk may be affected by weather (e.g., because of volume depletion). We therefore examined the association of temperature and humidity with the risk of recurrent gout attacks by conducting an internet-based case-crossover study in the United States (in 2003-2010) among subjects with a diagnosis of gout who had 1 or more attacks during 1 year of follow-up. We examined the association of temperature and humidity over the prior 48 hours with the risk of gout attacks using a time-stratified approach and conditional logistic regression. Among 632 subjects with gout, there was a significant dose-response relationship between mean temperature in the prior 48 hours and the risk of subsequent gout attack (P = 0.01 for linear trend). Higher temperatures were associated with approximately 40% higher risk of gout attack compared with moderate temperatures. There was a reverse J-shaped relationship between mean relative humidity and the risk of gout attacks (P = 0.03 for quadratic trend). The combination of high temperature and low humidity had the greatest association (odds ratio = 2.04, 95% confidence interval: 1.26, 3.30) compared with moderate temperature and relative humidity. Thus, high ambient temperature and possibly extremes of humidity were associated with an increased risk of gout attack, despite the likelihood that individuals are often in climate-controlled indoor environments.

The effect of secondary inorganic aerosols, soot and the geographical origin of air mass on acute myocardial infarction hospitalisations in Gothenburg, Sweden during 1985-2010: a case-crossover study

BACKGROUND

The relative importance of different sources of air pollution for cardiovascular disease is unclear. The aims were to compare the associations between acute myocardial infarction (AMI) hospitalisations in Gothenburg, Sweden and 1) the long-range transported (LRT) particle fraction, 2) the remaining particle fraction, 3) geographical air mass origin, and 4) influence of local dispersion during 1985-2010.

METHODS

A case-crossover design was applied using lag0 (the exposure the same day as hospitalisation), lag1 (exposure one day prior hospitalisation) and 2-day cumulative average exposure (CA2) (mean of lag0 and lag1). The LRT fractions included PMion (sum of sulphate, nitrate and ammonium) and soot measured at a rural site. The difference between urban PM10 (particulate matter with an aerodynamic diameter smaller than 10 μm) and rural PMion was a proxy for locally generated PM10 (PMrest). The daily geographical origin of air mass was estimated as well as days with limited or effective local dispersion. The entire year was considered, as well as warm and cold periods, and different time periods.

RESULTS

In total 28 215 AMI hospitalisations occurred during 26 years. PM10, PMion, PMrest and soot did not influence AMI for the entire year. In the cold period, the association was somewhat stronger for PMrest than for urban PM10; the strongest associations were observed during 1990-2000 between AMI and CA2 of PMrest (6.6% per inter-quartile range (IQR), 95% confidence interval 2.1 to 11.4%) and PM10 (4.1%, 95% CI 0.2% - 8.2%). Regarding the geographical air mass origins there were few associations. Days with limited local dispersion showed an association with AMI in the cold period of 2001-2010 (6.7%, 95% CI 0.0% - 13.0%).

CONCLUSIONS

In the cold period, locally generated PM and days with limited local dispersion affected AMI hospitalisations, indicating importance of local emissions from e.g. traffic.

The effects of fine particulate air pollution on daily mortality: a case-crossover study in a subtropical city, Taipei, Taiwan

This study was undertaken to determine whether there was an association between PM_2.5 levels and daily mortality in Taipei, Taiwan, the largest metropolitan city with a subtropical climate. Daily mortality, air pollution, and weather data for Taipei were obtained for the period from 2006–2008. The relative risk of daily mortality was estimated using a time-stratified case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single pollutant model, PM_2.5 showed association with total mortality both on warm (>23 °C) and cool days (<23 °C). There is no indication of an association between PM_2.5 and risk of death due to respiratory diseases both on warm and cool days. PM_2.5 had effects on the risk of death from cardiovascular diseases only on cool days. In the two-pollutant models, PM_2.5 remained effects on the risk of mortality for all cause and cardiovascular disease after the inclusion of SO₂ and O₃ both on warm and cool days. This study provides evidence that short-term exposure to PM_2.5 increased the risk of death for all cause and cardiovascular disease.

Exchangeability in the case-crossover design

In cohort and case-control studies, confounding that arises as a result of differences in the distribution of determinants of the outcome between exposure groups leading to non-exchangeability are addressed by restriction, matching or with statistical models. In case-only studies, this issue is addressed by comparing each individual with his/herself. Although case-only designs use self-matching and only include individuals who develop the outcome of interest, issues of non-exchangeability are identical to those that arise in traditional case-control and cohort studies. In this review, we describe one type of case-only design, the case-crossover design, and discuss how the concept of exchangeability can be used to understand issues of confounding, carryover effects, period effects and selection bias in case-crossover studies.

Susceptibility to mortality related to temperature and heat and cold wave duration in the population of Stockholm County, Sweden

Background

Ambient temperatures can cause an increase in mortality. A better understanding is needed of how health status and other factors modify the risk associated with high and low temperatures, to improve the basis of preventive measures. Differences in susceptibility to temperature and to heat and cold wave duration are relatively unexplored.

Objectives

We studied the associations between mortality and temperature and heat and cold wave duration, stratified by age and individual and medical factors.

Methods

Deaths among all residents of Stockholm County between 1990 and 2002 were linked to discharge diagnosis data from hospital admissions, and associations were examined using the time stratified case-crossover design. Analyses were stratified by gender, age, pre-existing disease, country of origin, and municipality level wealth, and adjusted for potential confounding factors.

Results

The effect on mortality by heat wave duration was higher for lower ages, in areas with lower wealth, for hospitalized patients younger than age 65. Odds were elevated among females younger than age 65, in groups with a previous hospital admission for mental disorders, and in persons with previous cardiovascular disease. Gradual increases in summer temperatures were associated with mortality in people older than 80 years, and with mortality in groups with a previous myocardial infarction and with chronic obstructive pulmonary disease (COPD) in the population younger than 65 years. During winter, mortality was associated with a decrease in temperature particularly in men and with the duration of cold spells for the population older than 80. A history of hospitalization for myocardial infarction increased the odds associated with cold temperatures among the population older than 65. Previous mental disease or substance abuse increased the odds of death among the population younger than 65.

Conclusion

To increase effectiveness, we suggest preventive efforts should not assume susceptible groups are the same for warm and cold days and heat and cold waves, respectively.

Fine particulate air pollution and hospital admissions for congestive heart failure: a case-crossover study in Taipei

This study was undertaken to determine whether there was an association between fine particles (PM₂.₅) levels and hospital admissions for congestive heart failure (CHF) in Taipei, Taiwan. Hospital admissions for CHF and ambient air pollution data for Taipei were obtained for the period 2006-2010. The relative risk of hospital admissions was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality and long-term time trends. For the single pollutant model (without adjustment for other pollutants), increased CHF admissions were significantly associated with PM₂.₅ both on warm days (>23 °C) and cool days (<23 °C), with an interquartile range increase associated with a 13% (95% CI = 9-17%) and 3% (95% CI = 0-7%) increase in CHF admissions, respectively. In the two-pollutant models, PM₂.₅ remained significant after the inclusion of SO₂ or O₃ both on warm and cool days. This study provides evidence that higher levels of PM₂.₅ increase the risk of hospital admissions for CHF.

Increased ultrafine particles and carbon monoxide concentrations are associated with asthma exacerbation among urban children

OBJECTIVES

Increased air pollutant concentrations have been linked to several asthma-related outcomes in children, including respiratory symptoms, medication use, and hospital visits. However, few studies have examined effects of ultrafine particles in a pediatric population. Our primary objective was to examine the effects of ambient concentrations of ultrafine particles on asthma exacerbation among urban children and determine whether consistent treatment with inhaled corticosteroids could attenuate these effects. We also explored the relationship between asthma exacerbation and ambient concentrations of accumulation mode particles, fine particles (≤2.5 micrograms [μm]; PM2.5), carbon monoxide, sulfur dioxide, and ozone. We hypothesized that increased 1-7 day concentrations of ultrafine particles and other pollutants would be associated with increases in the relative odds of an asthma exacerbation, but that this increase in risk would be attenuated among children receiving school-based corticosteroid therapy.

METHODS

We conducted a pilot study using data from 3 to 10 year-old children participating in the School-Based Asthma Therapy trial. Using a time-stratified case-crossover design and conditional logistic regression, we estimated the relative odds of a pediatric asthma visit treated with prednisone (n=96 visits among 74 children) associated with increased pollutant concentrations in the previous 7 days. We re-ran these analyses separately for children receiving medications through the school-based intervention and children in a usual care control group.

RESULTS

Interquartile range increases in ultrafine particles and carbon monoxide concentrations in the previous 7 days were associated with increases in the relative odds of a pediatric asthma visit, with the largest increases observed for 4-day mean ultrafine particles (interquartile range=2088p/cm(3); OR=1.27; 95% CI=0.90-1.79) and 7-day mean carbon monoxide (interquartile range=0.17ppm; OR=1.63; 95% CI=1.03-2.59). Relative odds estimates were larger among children receiving school-based inhaled corticosteroid treatment. We observed no such associations with accumulation mode particles, black carbon, fine particles (≤2.5μm), or sulfur dioxide. Ozone concentrations were inversely associated with the relative odds of a pediatric asthma visit.

CONCLUSIONS

These findings suggest a response to markers of traffic pollution among urban asthmatic children. Effects were strongest among children receiving preventive medications through school, suggesting that this group of children was particularly sensitive to environmental triggers. Medication adherence alone may be insufficient to protect the most vulnerable from environmental asthma triggers. However, further research is necessary to confirm this finding.

Short-term changes in ambient temperature and risk of ischemic stroke

Background

Despite consistent evidence of a higher short-term risk of cardiovascular mortality associated with ambient temperature, there have been discrepant findings on the association between temperature and ischemic stroke. Moreover, few studies have considered potential confounding by ambient fine particulate matter air pollution <2.5 μm in diameter (PM_2.5) and none have examined the impact of temperature changes on stroke in the subsequent hours rather than days. The aim of this study was to evaluate whether changes in temperature trigger an ischemic stroke in the following hours and days and whether humid days are particularly harmful.

Methods

We reviewed the medical records of 1,705 patients residing in the metropolitan region of Boston, Mass., USA, who were hospitalized with neurologist-confirmed ischemic stroke, and we abstracted data on the time of symptom onset and clinical characteristics. We obtained hourly meteorological data from the National Weather Service station and hourly PM_2.5 data from the Harvard ambient monitoring station. We used the time-stratified case-crossover design to assess the association between ischemic stroke and apparent temperature averaged over 1-7 days prior to stroke onset adjusting for PM_2.5. We assessed whether differences in apparent temperature trigger a stroke within shorter time periods by examining the association between stroke onset and apparent temperature levels averaged in 2-hour increments prior to stroke onset (0-2 h through 36-38 h). We tested whether the association varied by health characteristics or by PM_2.5, ozone or relative humidity.

Results

The incidence rate ratio of ischemic stroke was 1.09 (95% confidence interval 1.01-1.18) following a 5°C decrement in average apparent temperature over the 2 days preceding symptom onset. The higher risk associated with cooler temperatures peaked in the first 14-34 h. There was no statistically significant difference in the association between temperature and ischemic stroke across seasons. The risk of ischemic stroke was not meaningfully different across subgroups of patients defined by health characteristics. The association between ischemic stroke and ambient temperature was stronger on days with higher levels of relative humidity.

Conclusions

Lower temperatures are associated with a higher risk of ischemic stroke onset in both warm and cool seasons, and the risk is higher on days with higher levels of relative humidity. Based on this study and the body of literature on ambient temperature and cardiovascular events, identifying methods for mitigating cardiovascular risk may be warranted.

Ambient fine particulate air pollution triggers ST-elevation myocardial infarction, but not non-ST elevation myocardial infarction: a case-crossover study

Background

We and others have shown that increases in particulate air pollutant (PM) concentrations in the previous hours and days have been associated with increased risks of myocardial infarction, but little is known about the relationships between air pollution and specific subsets of myocardial infarction, such as ST-elevation myocardial infarction (STEMI) and non ST-elevation myocardial infarction (NSTEMI).

Methods

Using data from acute coronary syndrome patients with STEMI (n = 338) and NSTEMI (n = 339) and case-crossover methods, we estimated the risk of STEMI and NSTEMI associated with increased ambient fine particle (<2.5 um) concentrations, ultrafine particle (10-100 nm) number concentrations, and accumulation mode particle (100-500 nm) number concentrations in the previous few hours and days.

Results

We found a significant 18% increase in the risk of STEMI associated with each 7.1 μg/m³ increase in PM_2.5 concentration in the previous hour prior to acute coronary syndrome onset, with smaller, non-significantly increased risks associated with increased fine particle concentrations in the previous 3, 12, and 24 hours. We found no pattern with NSTEMI. Estimates of the risk of STEMI associated with interquartile range increases in ultrafine particle and accumulation mode particle number concentrations in the previous 1 to 96 hours were all greater than 1.0, but not statistically significant. Patients with pre-existing hypertension had a significantly greater risk of STEMI associated with increased fine particle concentration in the previous hour than patients without hypertension.

Conclusions

Increased fine particle concentrations in the hour prior to acute coronary syndrome onset were associated with an increased risk of STEMI, but not NSTEMI. Patients with pre-existing hypertension and other cardiovascular disease appeared particularly susceptible. Further investigation into mechanisms by which PM can preferentially trigger STEMI over NSTEMI within this rapid time scale is needed.

Relationship between hemorrhagic stroke hospitalization and exposure to fine particulate air pollution in Taipei, Taiwan

This study was undertaken to determine whether there was a correlation between fine particle (PM2.5) levels and hospital admissions for hemorrhagic stroke (HS) in Taipei, Taiwan. Hospital admissions for HS and ambient air pollution data for Taipei were obtained for the period 2006-2010. The relative risk of hospital admissions was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased HS admissions were significantly associated with PM2.5 levels both on warm days (>23°C) and cool days (<23°C), with an interquartile range rise associated with a 12% (95% CI = 7-18%) and 4% (95% CI = 0-8%) elevation in admissions for HS, respectively. In the two-pollutant models, PM2.5 remained significantly high after inclusion of SO2 or O3 on both warm and cool days. This study provides evidence that higher levels of PM2.5 increase the risk of hospital admissions for HS.

Short-term effect of fine particulate air pollution on daily mortality: a case-crossover study in a tropical city, Kaohsiung, Taiwan

Many studies have examined the short-term effects of air pollution on frequency of daily mortality over the past two decades. However, information on the relationship between levels of fine particles (PM(2.5)) and daily mortality is relatively sparse due to limited availability of monitoring data. Further the results are inconsistent. This study was undertaken to determine whether there was an association between PM(2.5) levels and daily mortality rate in Kaohsiung, Taiwan, a large industrial city with a tropical climate. Daily mortality rate, air pollution parameters, and weather data for Kaohsiung were obtained for the period from 2006 through 2008. The relative risk of daily mortality occurrence was estimated using a time-stratified case-crossover approach, controlling for (1) weather variables, (2) day of the week, (3) seasonality, and (4) long-term time trends. For the single-pollutant model (without adjustment for other pollutants), no significant effects were found between PM(2.5) and frequency of daily mortality on warm days (≥25°C). On cool days, PM(2.5) showed significant correlation with increased risk of mortality rate for all causes and circulatory diseases in single-pollutant model. There was no indication of an association between PM(2.5) and deaths due to respiratory diseases. The relationship appeared to be stronger on cool days. This study provided evidence of associations between short-term exposure to PM(2.5) and elevated risk of death for all cause and circulatory diseases.

Fine particulate air pollution and hospital admissions for asthma: a case-crossover study in Taipei

This study was undertaken to determine whether there was a correlation between fine particles (PM2.5) levels and hospital admissions for asthma in Taipei, Taiwan. Hospital admissions for asthma and ambient air pollution data for Taipei were obtained for the period of 2006-2010. The relative risk of hospital admissions for asthma was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased asthma admissions were significantly associated with PM2.5 levels both on warm days (>23°C) and cool days (<23°C), with an interquartile range rise associated with a 12% (95% CI = 6-18%) and 3% (95% CI = 0-8%) elevation in admissions for asthma, respectively. In the two-pollutant models, PM2.5 levels remained significant for increased asthma admissions after inclusion of SO2 or O3 both on warm and cool days. This study provides evidence that higher levels of PM2.5 elevate the risk of hospital admissions for asthma in Taiwan.

Fine particulate air pollution and hospital admissions for pneumonia in a subtropical city: Taipei, Taiwan

This study was undertaken to determine whether there was a correlation between fine particles (PM2.5) levels and hospital admissions for pneumonia in Taipei, Taiwan. Hospital admissions for pneumonia and ambient air pollution data for Taipei were obtained for the period from 2006 to 2010. The relative risk of hospital admissions for pneumonia was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased numbers of admissions for pneumonia were significantly associated with higher PM2.5 levels both on warm days (>23°C) and on cool days (<23°C). This was accompanied by an interquartile range elevation correlated with a 12% (95% CI = 16%-13%) and 4% (95% CI = 3%-6%) rise in number of admissions for pneumonia, respectively. In the two-pollutant models, PM2.5 remained significant after inclusion of sulfur dioxide (SO₂) or ozone (O₃) both on warm and on cool days. This study provides evidence that higher levels of PM2.5 increase the risk of hospital admissions for pneumonia.

Short-term effects of fine particulate air pollution on hospital admissions for respiratory diseases: a case-crossover study in a tropical city

This study was undertaken to determine whether there was a correlation between fine particles (PM2.5) levels and hospital admissions for respiratory diseases in Kaohsiung, Taiwan. Hospital admissions for respiratory diseases including pneumonia, asthma, and chronic obstructive pulmonary disease (COPD) and ambient air pollution data for Kaohsiung were obtained for the period 2006-2010. The relative risk (RR) of hospital admissions for respiratory diseases was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and chronic time trends. For the single-pollutant model (without adjustment for other pollutants), increased number of admissions for respiratory diseases were significantly associated with higher PM2.5 levels only on cool days (<25°C), with an interquartile range rise associated with a 50 (95% CI% = 45-55%), 40% (95% CI = 25-58%), and 46% (95% CI = 36-57%) elevation in frequency of admissions for pneumonia, asthma, and COPD, respectively. In the two-pollutant models, PM2.5 levels remained significant even controlling for sulfur dioxide, nitrogen dioxide, carbon monoxide, or ozone on cool days. This study provides evidence that higher levels of PM2.5 increase the risk of hospital admissions for respiratory diseases in Taiwan.

Association between PM2.5 and primary care visits due to asthma attack in Japan: relation to Beijing's air pollution episode in January 2013

AIM

In January 2013, extremely high concentrations of fine particles (PM2.5) were observed around Beijing, China. In Japan, the health effects of transboundary air pollution have been a matter of concern. We examined the association between the levels of outdoor PM2.5 and other air pollutants with primary care visits (PCVs) at night due to asthma attack in Himeji City, western Japan.

METHODS

A case-crossover study was conducted in a primary care clinic in Himeji City, Japan, involving 112 subjects aged 0-80 years who visited the clinic due to an asthma attack between 9 p.m. and 6 a.m. during the period January-March, 2013. Daily concentrations of particulate matter, ozone, nitrogen dioxide, and some meteorological elements were measured, and a conditional logistic regression model was used to estimate the odds ratios (OR) of PCVs per unit increment in air pollutants or meteorological elements.

RESULTS

Of the 112 subjects, 76 (68 %) were aged <15 years. We did not note any association between daily PM2.5 levels and PCVs due to asthma attack at night. A positive relation between ozone and PCVs due to asthma attack was detected. The OR per 10 ppb increment in daily mean ozone the day before the visit was 2.31 (95 % confidence interval 1.16-4.61).

CONCLUSION

These findings do not support an association between daily mean concentration of PM2.5 and PCVs at night. However, we did find evidence suggesting that ozone is associated with PCVs.

Bayesian analysis of time-series data under case-crossover designs: posterior equivalence and inference

Case-crossover designs are widely used to study short-term exposure effects on the risk of acute adverse health events. While the frequentist literature on this topic is vast, there is no Bayesian work in this general area. The contribution of this paper is twofold. First, the paper establishes Bayesian equivalence results that require characterization of the set of priors under which the posterior distributions of the risk ratio parameters based on a case-crossover and time-series analysis are identical. Second, the paper studies inferential issues under case-crossover designs in a Bayesian framework. Traditionally, a conditional logistic regression is used for inference on risk-ratio parameters in case-crossover studies. We consider instead a more general full likelihood-based approach which makes less restrictive assumptions on the risk functions. Formulation of a full likelihood leads to growth in the number of parameters proportional to the sample size. We propose a semi-parametric Bayesian approach using a Dirichlet process prior to handle the random nuisance parameters that appear in a full likelihood formulation. We carry out a simulation study to compare the Bayesian methods based on full and conditional likelihood with the standard frequentist approaches for case-crossover and time-series analysis. The proposed methods are illustrated through the Detroit Asthma Morbidity, Air Quality and Traffic study, which examines the association between acute asthma risk and ambient air pollutant concentrations.

Fine particulate air pollution and hospital admissions for chronic obstructive pulmonary disease: a case-crossover study in Taipei

We undertook this study to investigate whether there is an association between atmospheric fine particles (PM2.5) levels and inpatient admissions for chronic obstructive pulmonary disease (COPD) in Taipei, Taiwan. Data on inpatient admissions for COPD and ambient on air pollution levels in Taipei were obtained for years 2006 to 2010. We estimated the relative risk of inpatient admissions for COPD using a case-crossover design with the following control variables: weather measures, day of the week, seasonality, and long-term time trends. For the single-pollutant model (not controlling for other atmospheric pollutants), COPD admissions were significantly and positively associated with higher PM2.5 levels during both warm days (>23 °C) and cool days (<23 °C), with an interquartile range increase of 12% (95% CI = 8-16%) and 3% (95% CI = 0-7%) in COPD admissions, respectively. In the two-pollutant models, PM2.5 remained significant even controlling for SO2 or O3 on both warm and cool days. Taken as a whole, our study demonstrates that higher levels of PM2.5 may increase the risk of inpatient admissions for COPD.

Refined ambient PM2.5 exposure surrogates and the risk of myocardial infarction

Using a case-crossover study design and conditional logistic regression, we compared the relative odds of transmural (full-wall) myocardial infarction (MI) calculated using exposure surrogates that account for human activity patterns and the indoor transport of ambient PM(2.5) with those calculated using central-site PM(2.5) concentrations to estimate exposure to PM(2.5) of outdoor origin (exposure to ambient PM(2.5)). Because variability in human activity and indoor PM(2.5) transport contributes exposure error in epidemiologic analyses when central-site concentrations are used as exposure surrogates, we refer to surrogates that account for this variability as "refined" surrogates. As an alternative analysis, we evaluated whether the relative odds of transmural MI associated with increases in ambient PM(2.5) is modified by residential air exchange rate (AER), a variable that influences the fraction of ambient PM(2.5) that penetrates and persists indoors. Use of refined exposure surrogates did not result in larger health effect estimates (ORs=1.10-1.11 with each interquartile range (IQR) increase), narrower confidence intervals, or better model fits compared with the analysis that used central-site PM(2.5). We did observe evidence for heterogeneity in the relative odds of transmural MI with residential AER (effect-modification), with residents of homes with higher AERs having larger ORs than homes in lower AER tertiles. For the level of exposure-estimate refinement considered here, our findings add support to the use of central-site PM(2.5) concentrations for epidemiological studies that use similar case-crossover study designs. In such designs, each subject serves as his or her own matched control. Thus, exposure error related to factors that vary spatially or across subjects should only minimally impact effect estimates. These findings also illustrate that variability in factors that influence the fraction of ambient PM(2.5) in indoor air (e.g., AER) could possibly bias health effect estimates in study designs for which a spatiotemporal comparison of exposure effects across subjects is conducted.

Interaction between air pollution exposure and genes in relation to levels of inflammatory markers and risk of myocardial infarction

OBJECTIVES

Air pollution exposure induces cardiovascular effects, possibly via systemic inflammation and coagulation misbalance. Genetic variation may determine individual susceptibility. Our aim was to investigate effect modification by inflammation (Interleukin6 (IL6), tumour necrosis factor-α (TNF-α)) and coagulation (fibrinogen Bβ, plasminogen activator inhibitor-1 (PAI-1)) gene variants on the effect of long-term or short-term air pollution exposure on both blood marker levels and non-fatal myocardial infarction (MI) risk.

DESIGN

Population-based case-control study with a nested case-crossover study. Gene-environment interactions for short-term and long-term air pollution on blood marker levels were studied in population controls, for long-term exposure on MI risk using case-control design, and for short-term exposure on MI onset using case-crossover design.

SETTING

The Stockholm Heart Epidemiology Programme (SHEEP) conducted in 1992-1994 in Stockholm, Sweden. Spatial modelling was used to assess long-term (up to 30 years retrospectively) air pollution exposure to traffic-NO2 and heating-SO2 emissions at home addresses. Urban background NO2, SO2, PM10 and O3 measurements were used to estimate short-term (up to 5 days) air pollution exposure.

PARTICIPANTS

1192 MI cases and 1506 population controls aged 45-70 years.

OUTCOMES

The levels of blood markers of inflammation (IL-6, TNF-α) and coagulation (fibrinogen, PAI-1) and MI risk.

RESULTS

We observed gene-environment interaction for several IL6 and TNF SNPs in relation to inflammation blood marker levels. One-year traffic-NO2 exposure was associated with higher IL-6 levels with each additional IL6-174C allele, and 1-year heating-SO2 exposure with higher levels of TNF-α in TNF-308AA homozygotes versus -308G carriers. Short-term air pollution exposure also interacted with IL6 and TNF in relation to marker levels. The risk of MI followed the effect on blood markers in each genotype group.

CONCLUSIONS

Genetic variants in IL6 and TNF may modify effects of long-term and short-term air pollution exposure on inflammatory marker levels and MI risk.

Short-term associations between fine and coarse particulate matter and hospitalizations in Southern Europe: results from the MED-PARTICLES project

BACKGROUND

Evidence on the short-term effects of fine and coarse particles on morbidity in Europe is scarce and inconsistent.

OBJECTIVES

We aimed to estimate the association between daily concentrations of fine and coarse particles with hospitalizations for cardiovascular and respiratory conditions in eight Southern European cities, within the MED-PARTICLES project.

METHODS

City-specific Poisson models were fitted to estimate associations of daily concentrations of particulate matter with aerodynamic diameter ≤ 2.5 μm (PM2.5), ≤ 10 μm (PM10), and their difference (PM2.5-10) with daily counts of emergency hospitalizations for cardiovascular and respiratory diseases. We derived pooled estimates from random-effects meta-analysis and evaluated the robustness of results to co-pollutant exposure adjustment and model specification. Pooled concentration-response curves were estimated using a meta-smoothing approach.

RESULTS

We found significant associations between all PM fractions and cardiovascular admissions. Increases of 10 μg/m3 in PM2.5, 6.3 μg/m3 in PM2.5-10, and 14.4 μg/m3 in PM10 (lag 0-1 days) were associated with increases in cardiovascular admissions of 0.51% (95% CI: 0.12, 0.90%), 0.46% (95% CI: 0.10, 0.82%), and 0.53% (95% CI: 0.06, 1.00%), respectively. Stronger associations were estimated for respiratory hospitalizations, ranging from 1.15% (95% CI: 0.21, 2.11%) for PM10 to 1.36% (95% CI: 0.23, 2.49) for PM2.5 (lag 0-5 days).

CONCLUSIONS

PM2.5 and PM2.5-10 were positively associated with cardiovascular and respiratory admissions in eight Mediterranean cities. Information on the short-term effects of different PM fractions on morbidity in Southern Europe will be useful to inform European policies on air quality standards.

The triggering of myocardial infarction by fine particles is enhanced when particles are enriched in secondary species

Previous studies have reported an increased risk of myocardial infarction (MI) associated with acute increases in PM concentration. Recently, we reported that MI/fine particle (PM2.5) associations may be limited to transmural infarctions. In this study, we retained data on hospital discharges with a primary diagnosis of acute myocardial infarction (using International Classification of Diseases ninth Revision [ICD-9] codes), for those admitted January 1, 2004 to December 31, 2006, who were ≥ 18 years of age, and were residents of New Jersey at the time of their MI. We excluded MI with a diagnosis of a previous MI and MI coded as a subendocardial infarction, leaving n = 1563 transmural infarctions available for analysis. We coupled these health data with PM2.5 species concentrations predicted by the Community Multiscale Air Quality chemical transport model, ambient PM2.5 concentrations, and used the same case-crossover methods to evaluate whether the relative odds of transmural MI associated with increased PM2.5 concentration is modified by the PM2.5 composition/mixture (i.e., mass fractions of sulfate, nitrate, elemental carbon, organic carbon, and ammonium). We found the largest relative odds estimates on the days with the highest tertile of sulfate mass fraction (OR = 1.13; 95% CI = 1.00, 1.27), nitrate mass fraction (OR = 1.18; 95% CI = 0.98, 1.35), and ammonium mass fraction (OR = 1.13; 95% CI = 1.00 1.28), and the lowest tertile of EC mass fraction (OR = 1.17; 95% CI = 1.03, 1.34). Air pollution mixtures on these days were enhanced in pollutants formed through atmospheric chemistry (i.e., secondary PM2.5) and depleted in primary pollutants (e.g., EC). When mixtures were laden with secondary PM species (sulfate, nitrate, and/or organics), we observed larger relative odds of myocardial infarction associated with increased PM2.5 concentrations. Further work is needed to confirm these findings and examine which secondary PM2.5 component(s) is/are responsible for an acute MI response.

Ambient ozone concentrations and the risk of perforated and nonperforated appendicitis: a multicity case-crossover study

BACKGROUND

Environmental determinants of appendicitis are poorly understood. Past work suggests that air pollution may increase the risk of appendicitis.

OBJECTIVES

We investigated whether ambient ground-level ozone (O3) concentrations were associated with appendicitis and whether these associations varied between perforated and nonperforated appendicitis.

METHODS

We based this time-stratified case-crossover study on 35,811 patients hospitalized with appendicitis from 2004 to 2008 in 12 Canadian cities. Data from a national network of fixed-site monitors were used to calculate daily maximum O3 concentrations for each city. Conditional logistic regression was used to estimate city-specific odds ratios (ORs) relative to an interquartile range (IQR) increase in O3 adjusted for temperature and relative humidity. A random-effects meta-analysis was used to derive a pooled risk estimate. Stratified analyses were used to estimate associations separately for perforated and nonperforated appendicitis.

RESULTS

Overall, a 16-ppb increase in the 7-day cumulative average daily maximum O3 concentration was associated with all appendicitis cases across the 12 cities (pooled OR = 1.07; 95% CI: 1.02, 1.13). The association was stronger among patients presenting with perforated appendicitis for the 7-day average (pooled OR = 1.22; 95% CI: 1.09, 1.36) when compared with the corresponding estimate for nonperforated appendicitis [7-day average (pooled OR = 1.02, 95% CI: 0.95, 1.09)]. Heterogeneity was not statistically significant across cities for either perforated or nonperforated appendicitis (p > 0.20).

CONCLUSIONS

Higher levels of ambient O3 exposure may increase the risk of perforated appendicitis.

Acute exposure to air pollution triggers atrial fibrillation

OBJECTIVES

This study sought to evaluate the association of air pollution with the onset of atrial fibrillation (AF).

BACKGROUND

Air pollution in general and more specifically particulate matter has been associated with cardiovascular events. Although ventricular arrhythmias are traditionally thought to convey the increased cardiovascular risk, AF may also contribute.

METHODS

Patients with dual chamber implantable cardioverter-defibrillators (ICDs) were enrolled and followed prospectively. The association of AF onset with air quality including ambient particulate matter <2.5 μm aerodynamic diameter (PM2.5), black carbon, sulfate, particle number, NO2, SO2, and O3 in the 24 h prior to the arrhythmia was examined utilizing a case-crossover analysis. In sensitivity analyses, associations with air pollution between 2 and 48 h prior to the AF were examined.

RESULTS

Of 176 patients followed for an average of 1.9 years, 49 patients had 328 episodes of AF lasting ≥ 30 s. Positive but nonsignificant associations were found for PM2.5 in the prior 24 h, but stronger associations were found with shorter exposure windows. The odds of AF increased by 26% (95% confidence interval: 8% to 47%) for each 6.0 μg/m(3) increase in PM2.5 in the 2 h prior to the event (p = 0.004). The odds of AF were highest at the upper quartile of mean PM2.5.

CONCLUSIONS

PM was associated with increased odds of AF onset within hours following exposure in patients with known cardiac disease. Air pollution is an acute trigger of AF, likely contributing to the pollution-associated adverse cardiac outcomes observed in epidemiological studies.

Quantitative analysis of burden of infectious diarrhea associated with floods in northwest of anhui province, china: a mixed method evaluation

Background

Persistent and heavy rainfall in the upper and middle Huaihe River of China brought about severe floods during the end of June and July 2007. However, there has been no assessment on the association between the floods and infectious diarrhea. This study aimed to quantify the impact of the floods in 2007 on the burden of disease due to infectious diarrhea in northwest of Anhui Province.

Methods

A time-stratified case-crossover analysis was firstly conducted to examine the relationship between daily cases of infectious diarrhea and the 2007 floods in Fuyang and Bozhou of Anhui Province. Odds ratios (ORs) of the flood risk were quantified by conditional logistic regression. The years lived with disability (YLDs) of infectious diarrhea attributable to floods were then estimated based on the WHO framework of the calculating potential impact fraction in the Burden of Disease study.

Results

A total of 197 infectious diarrheas were notified during the exposure and control periods in the two study areas. The strongest effect was shown with a 2-day lag in Fuyang and a 5-day lag in Bozhou. Multivariable analysis showed that floods were significantly associated with an increased risk of the number cases of infectious diarrhea (OR = 3.175, 95%CI: 1.126–8.954 in Fuyang; OR = 6.754, 95%CI: 1.954–23.344 in Bozhou). Attributable YLD per 1000 of infectious diarrhea resulting from the floods was 0.0081 in Fuyang and 0.0209 in Bozhou.

Conclusions

Our findings confirm that floods have significantly increased the risks of infectious diarrhea in the study areas. In addition, prolonged moderate flood may cause more burdens of infectious diarrheas than severe flood with a shorter duration. More attention should be paid to particular vulnerable groups, including younger children and elderly, in developing public health preparation and intervention programs. Findings have significant implications for developing strategies to prevent and reduce health impact of floods.

Association of ambient air pollution and meteorological factors with primary care visits at night due to asthma attack

AIM

The association of outdoor air pollution and meteorological elements with primary care visits at night due to asthma attack was studied.

METHODS

A case-crossover study was conducted in a primary care clinic in Himeji City, Japan. The subjects were 956 children aged 0-14 years who visited the clinic with an asthma attack between the hours of 9 p.m. and 6 a.m. Daily concentrations of particulate matter, ozone, nitrogen dioxide, and a number of meteorological elements were measured, and a conditional logistic regression model was used to estimate odds ratios (ORs) of primary care visits per unit increment of air pollutants or meteorological elements. The analyses took into consideration the effects of seasonality.

RESULTS

Of the 956 children, 73 (7.6 %) were aged <2 years and 417 (43.6 %) were aged 2-5 years. No association between daily ozone levels and primary care visits due to asthma attack at night in the spring or summer was found. An inverse relation between suspended particulate matter and primary care visits due to asthma attack was detected in the winter. ORs in the summer per degree increment in daily mean temperature was 1.31 [95 % confidential interval (CI) 1.09-1.56], and ORs in the autumn per hourly increment in daily hours of sunshine was 0.94 (95 % CI 0.90-0.99).

CONCLUSION

The findings of our study fail to support any association between daily mean concentration of air pollutant and primary care visits at night. However, we did find evidence indicating that certain meteorological elements may be associated with primary care visits.

Association between ambient temperature and acute myocardial infarction hospitalisations in Gothenburg, Sweden: 1985-2010

Cardiovascular disease (CVD) is the number one cause of death globally and evidence is steadily increasing on the role of non-traditional risk factors such as meteorology and air pollution. Nevertheless, many research gaps remain, such as the association between these non-traditional risk factors and subtypes of CVD, such as acute myocardial infarction (AMI). The objective of this study was to investigate the association between daily ambient temperature and AMI hospitalisations using a case-crossover design in Gothenburg, Sweden (1985–2010). A secondary analysis was also performed for out-of-hospital ischemic heart disease (IHD) deaths. Susceptible groups by age and sex were explored. The entire year as well as the warm (April−September) and cold periods (October–March) were considered. In total 28 215 AMI hospitalisations (of 22 475 people) and 21 082 out-of-hospital IHD deaths occurred during the 26-year study period. A linear exposure-response corresponding to a 3% and 7% decrease in AMI hospitalisations was observed for an inter-quartile range (IQR) increase in the 2-day cumulative average of temperature during the entire year (11°C) and the warm period (6°C), respectively, with and without adjustment for PM₁₀, NO₂, NO_x or O₃. No heat waves occurred during the warm period. No evidence of an association in the cold period nor any association between temperature and IHD deaths in the entire year, warm or cold periods - with and without adjusting for PM₁₀, NO₂, NO_x or O₃ was found. No susceptible groups, based on age or sex, were identified either. The inverse association between temperature and AMI hospitalisations (entire year and warm period) in Gothenburg is in accordance with the majority of the few other studies that investigated this subtype of CVD.

Estimation of short-term effects of air pollution on stroke hospital admissions in Wuhan, China

Background and Objective

High concentrations of air pollutants have been linked to increased incidence of stroke in North America and Europe but not yet assessed in mainland China. The aim of this study is to evaluate the association between stroke hospitalization and short-term elevation of air pollutants in Wuhan, China.

Methods

Daily mean NO₂, SO₂ and PM₁₀ levels, temperature and humidity were obtained from 2006 through 2008. Data on stroke hospitalizations (ICD 10: I60–I69) at four hospitals in Wuhan were obtained for the same period. A time-stratified case-crossover design was performed by season (April-September and October-March) to assess effects of pollutants on stroke hospital admissions.

Results

Pollution levels were higher in October-March with averages of 136.1 µg/m³ for PM₁₀, 63.6 µg/m³ for NO₂ and 71.0 µg/m³ for SO₂ than in April-September when averages were 102.0 µg/m³, 41.7 µg/m³ and 41.7 µg/m³, respectively (p<.001). During the cold season, every 10 µg/m³ increase in NO₂ was associated with a 2.9% (95%C.I. 1.2%–4.6%) increase in stroke admissions on the same day. Every 10 ug/m³ increase in PM₁₀ daily concentration was significantly associated with an approximate 1% (95% C.I. 0.1%–1.4%) increase in stroke hospitalization. A two-pollutant model indicated that NO₂ was associated with stroke admissions when controlling for PM₁₀. During the warm season, no significant associations were noted for any of the pollutants.

Conclusions

Exposure to NO₂ is significantly associated with stroke hospitalizations during the cold season in Wuhan, China when pollution levels are 50% greater than in the warm season. Larger and multi-center studies in Chinese cities are warranted to validate our findings.

Cold-related mortality due to cardiovascular diseases, respiratory diseases and cancer: a case-crossover study

OBJECTIVES

The aim of this study was to identify the relationship between low temperatures in winter and mortality due to cancer, cardiovascular diseases and respiratory diseases.

STUDY DESIGN

Case-crossover study.

METHODS

A case-crossover study was performed in Cantabria (northern Spain) in the years 2004-2005; 3948 deaths were included. Odds ratios were estimated using conditional logistic regression, stratified by age, sex, and delay of exposure to low temperatures.

RESULTS

There was an inverse dose-response relationship between temperature and mortality in the three causes of death studied; this result was consistent across genders and age groups. The higher OR for cancer mortality was seen on the first day of exposure (OR = 4.91; 95% CI: 1.65-13.07 in the whole population), and it decreased when exposure over several days in a row was considered; people aged 75 years or more were especially susceptible to cold temperatures (OR = 17.9; 95% CI: 2.38-134.8). Cardiovascular (OR = 2.63; 95% CI: 1.88-3.67) and respiratory mortality (OR = 2.72; 95% CI: 1.46-5.08) showed a weaker effect.

CONCLUSION

There is a striking association between the extreme cold temperatures and mortality from cancer, not previously reported, which is more remarkable in the elderly. These results could be explained by a harvesting effect in which the cold acts as a trigger of death in terminally ill patients at high risk of dying a few days or weeks later.

Acute effects of urban and industrial pollution in a government-designated "Environmental risk area": the case of Brindisi, Italy

Exposure to air pollutants has been associated with increased hospital admissions (HAs) for respiratory and cardiovascular diseases. This work describes a short-term epidemiological study in Brindisi, a highly industrialized town in Southern Italy. The effects of daily exposure to PM10 and NO2 on daily HAs for cardiac, respiratory, and cerebrovascular diseases were investigated by means of a case-crossover design in the period 2001-2007. Results showed positive associations between PM10 and HAs for cardiac and respiratory diseases and between NO2 and HAs for all the categories of diseases considered, particularly among females. Although not statistically significant, increased risk was observed for wind blowing from the port and the industrial area. Findings confirm the health risks associated with ambient air pollution exposure, even though NO2 and PM10 concentrations were below the legal limits. This may be due to the complex scenario of emissions in the area, which should be better investigated.

Out-of-hospital cardiac arrests and outdoor air pollution exposure in Copenhagen, Denmark

Cardiovascular disease is the number one cause of death globally and air pollution can be a contributing cause. Acute myocardial infarction and cardiac arrest are frequent manifestations of coronary heart disease. The objectives of the study were to investigate the association between 4 657 out-of-hospital cardiac arrests (OHCA) and hourly and daily outdoor levels of PM₁₀, PM_2.5, coarse fraction of PM (PM_10-2.5), ultrafine particle proxies, NO_x, NO₂, O₃ and CO in Copenhagen, Denmark, for the period 2000–2010. Susceptible groups by age and sex was also investigated. A case-crossover design was applied. None of the hourly lags of any of the pollutants were significantly associated with OHCA events. The strongest association with OHCA events was observed for the daily lag4 of PM_2.5, lag3 of PM₁₀, lag3 of PM_10-2.5, lag3 of NO_x and lag4 of CO. An IQR increase of PM_2.5 and PM₁₀ was associated with a significant increase of 4% (95% CI: 0%; 9%) and 5% (95% CI: 1%; 9%) in OHCA events with 3 days lag, respectively. None of the other daily lags or other pollutants was significantly associated with OHCA events. Adjustment for O₃ slightly increased the association between OHCA and PM_2.5 and PM₁₀. No susceptible groups were identified.

Short-term effects of fine particulate air pollution on emergency room visits for cardiac arrhythmias: a case-crossover study in Taipei

This study was undertaken to determine whether there was an association between fine particles (PM₂.₅) levels and number of emergency room (ER) visits for cardiac arrhythmias in Taipei, Taiwan. ER visits for cardiac arrhythmias and ambient air pollution data for Taipei were obtained for the period 2006-2010. The relative risk (RR) of ER visits was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased numbers of ER cardiac arrhythmia visits were significantly associated with PM₂.₅ on both warm days (>23°C) and cool days (< 23°C), with an interquartile range rise associated with a 10% (95% CI = -15%) and 4% (95% CI = 0-8%) elevation in number of ER visits for cardiac arrhythmias, respectively. In the two-pollutant models, PM₂.₅ levels remained significant after inclusion of sulfur dioxide (SO₂) or ozone (O₃) on both warm and cool days. This study provides evidence that higher levels of PM₂.₅ increase the risk of number of ER visits for cardiac arrhythmias.

Short-term effects of fine particulate air pollution on ischemic stroke occurrence: a case-crossover study

This study was undertaken to determine whether there was a correlation between fine particles (PM2.5) levels and hospital admissions for ischemic stroke (IS) in Taipei, Taiwan. Hospital admissions for IS and ambient air pollution data for Taipei were obtained for the period from 2006-2010. The relative risk of hospital admissions was estimated using a case-crossover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. For the single-pollutant model (without adjustment for other pollutants), increased admissions for IS were significantly associated with higher levels of PM2.5 on both warm days (>23°C) and cool days (<23°C), with an interquartile range rise associated with a 11% (95% CI = 8-14%) and 4% (95% CI = 2-7%) elevation in admissions for IS, respectively. In the two-pollutant models, PM2.5 remained significantly increased after inclusion of sulfur dioxide (SO2) or ozone (O3) on both warm and cool days. This study provides evidence that higher levels of PM2.5 enhance the risk of hospital admissions for IS.

Fine particulate air pollution and hospital admissions for myocardial infarction in a subtropical city: Taipei, Taiwan

This study was undertaken to determine whether there was a correlation between fine particles (PM2.5) levels and hospital admissions for myocardial infarction (MI) in Taipei, Taiwan. Hospital admissions for MI and ambient air pollution data for Taipei were obtained for the period 2006-2010. The relative risk of hospital admissions for MI was estimated using a casecrossover approach, controlling for weather variables, day of the week, seasonality, and longterm time trends. For the single-pollutant model (without adjustment for other pollutants), increased numbers of MI admissions were significantly associated with higher PM2.5 levels both on warm days (>23°C) and on cool days (<23°C). This was accompanied by an interquartile range elevation correlated with a 10% (95% CI = 6-15%) and 5% (95% CI = 1-9%) rise in number of MI admissions, respectively. In the two-pollutant models, PM2.5 remained significant after inclusion of SO2 or O3 on both warm and cool days. This study provides evidence that higher levels of PM2.5 increase the risk of hospital admissions for MI.

Observational approaches in the study of the effects of Total Suspended Particulates (TSP) exposure

Literature contains mainly reports of observations based on time-series, or those of a case-crossover analysis design or, although less frequently, case control studies. However, data obtained by different approaches are difficult to compare based on different and non-homogenous population. The principal aim of this research was to compare the estimated risks obtained by differing approaches based on the same population study in the period 2006-2009. The data were based on a total of 44,200 residents in the city of Turin, hospitalised for respiratory diseases (ICD 460-519) in the period 2006-2009. Total suspended particulates (TSP), measured in µg/m(3), are the most commonly used predictors of urban pollution. The association between hospital admission for respiratory diseases and TSP exposure was investigated using at the same time the time-series, case-crossover and case-control approaches. The analyses show a general comparability of the case-crossover design stratified for time and the time-series approach, and the case control approach provided a more unstable estimation of risks. In conclusion, our results seem to indicate that the different approaches studied seem to offer comparable results.