Seasonal variation in cause-specific mortality: are there high-risk groups? 25-year follow-up of civil servants from the first Whitehall study

Excess winter morbidity and mortality: do housing and socio-economic status have an effect?

OBJECTIVE

To review the published research evidence on the links between excess winter mortality (EWM) or excess winter hospitalization (EWH) and housing quality or socioeconomic status (SES).

DESIGN

Systematic review.

CRITERIA

Linked data on EWM or EWH and potential associations with housing quality or SES.

RESULTS

No consistent relations between SES and EWM or EWH. The results for housing quality are also inconsistent, with some studies showing a weak protective effect of home heating.

CONCLUSION

Studies to date do not provide good evidence that housing quality or SES factors affect EWM and EWH. More research is needed, particularly studies using individual level housing and SES data. Controlled trials of interventions would be desirable.

Comparing estimates of influenza-associated hospitalization and death among adults with congestive heart failure based on how influenza season is defined

BACKGROUND

There is little consensus about how the influenza season should be defined in studies that assess influenza-attributable risk. The objective of this study was to compare estimates of influenza-associated risk in a defined clinical population using four different methods of defining the influenza season.

METHODS

Using the Studies of Left Ventricular Dysfunction (SOLVD) clinical database and national influenza surveillance data from 1986-87 to 1990-91, four definitions were used to assess influenza-associated risk: (a) three-week moving average of positive influenza isolates is at least 5%, (b) three-week moving average of positive influenza isolates is at least 10%, (c) first and last positive influenza isolate are identified, and (d) 5% of total number of positive isolates for the season are obtained. The clinical data were from adults aged 21 to 80 with physician-diagnosed congestive heart failure. All-cause hospitalization and all-cause mortality during the influenza seasons and non-influenza seasons were compared using four definitions of the influenza season. Incidence analyses and Cox regression were used to assess the effect of exposure to influenza season on all-cause hospitalization and death using all four definitions.

RESULTS

There was a higher risk of hospitalization associated with the influenza season, regardless of how the start and stop of the influenza season was defined. The adjusted risk of hospitalization was 8 to 10 percent higher during the influenza season compared to the non-influenza season when the different definitions were used. However, exposure to influenza was not consistently associated with higher risk of death when all definitions were used. When the 5% moving average and first/last positive isolate definitions were used, exposure to influenza was associated with a higher risk of death compared to non-exposure in this clinical population (adjusted hazard ratios [HR], 1.16; 95% confidence interval [CI], 1.04 to 1.29 and adjusted HR, 1.19; 95% CI, 1.06 to 1.33, respectively).

CONCLUSION

Estimates of influenza-attributable risk may vary depending on how influenza season is defined and the outcome being assessed.

Seasonal variation in surgical outcomes as measured by the American College of Surgeons-National Surgical Quality Improvement Program (ACS-NSQIP)

OBJECTIVE

We hypothesize that the systems of care within academic medical centers are sufficiently disrupted with the beginning of a new academic year to affect patient outcomes.

METHODS

This observational multiinstitutional cohort study was conducted by analysis of the National Surgical Quality Improvement Program-Patient Safety in Surgery Study database. The 30-day morbidity and mortality rates were compared between 2 periods of care: (early group: July 1 to August 30) and late group (April 15 to June 15). Patient baseline characteristics were first compared between the early and late periods. A prediction model was then constructed, via stepwise logistic regression model with a significance level for entry and a significance level for selection of 0.05.

RESULTS

There was 18% higher risk of postoperative morbidity in the early (n = 9941) versus the late group (n = 10313) (OR 1.18, 95%, CI 1.07-1.29, P = 0.0005, c-index 0.794). There was a 41% higher risk for mortality in the early group compared with the late group (OR 1.41, CI 1.11-1.80, P = 0.005, c-index 0.938). No significant trends in patient risk over time were noted.

CONCLUSION

Our data suggests higher rates of postsurgical morbidity and mortality related to the time of the year. Further study is needed to fully describe the etiologies of the seasonal variation in outcomes.

Risk of hospitalization during influenza season among a cohort of patients with congestive heart failure

It is uncertain whether hospitalization among patients with congestive heart failure (CHF) increases during the influenza season. This retrospective cohort study used influenza surveillance data from the United States (1986-1987 to 1990-1991), clinical information from the Studies of Left Ventricular Dysfunction (SOLVD) database, and daily temperature data from the National Climatic Data Center to assess the effect of influenza season on hospitalizations in this cohort of patients. The overall hospitalization rate was higher during influenza seasons compared to non-influenza seasons [relative risk (RR) 1.08, 95% confidence interval (CI) 1.01-1.16]. Multivariable Cox modelling revealed an adjusted hazard ratio (HR) of 1.11 for hospitalization during the influenza season (95% CI 1.03-1.20, P=0.005). Overall death rates were also higher during influenza seasons than non-influenza seasons (RR 1.09, 95% CI 0.97-1.21), but the corresponding adjusted HR for death was not significant (HR 1.01, 95% CI 0.98-1.24, P=0.11). Patients with CHF have a greater risk of hospitalization during the influenza season than in the non-influenza season, supporting the current belief that patients with CHF should be regarded as a high-risk group.

Winter excess in hospital admissions, in-patient mortality and length of acute hospital stay in stroke: a hospital database study over six seasonal years in Norfolk, UK

BACKGROUND

Several studies have examined the incidence and mortality of stroke in relation to season. However, the evidence is conflicting partly due to variation in the populations (community vs. hospital-based), and in climatic conditions between studies. Moreover, they may not have been able to take into account the age, sex and stroke type of the study population. We hypothesized that the age, sex and type of stroke are major determinants of the presence or absence of winter excess in morbidity and mortality associated with stroke.

METHODS

We analyzed a hospital-based stroke register from Norfolk, UK to examine our prior hypothesis. Using Curwen's method, we performed stratified sex-specific analyses by (1) seasonal year and (2) quartiles of patients' age and stroke subtype and calculated the winter excess for the number of admissions, in-patient deaths and length of acute hospital stay.

RESULTS

There were 5,481 patients (men=45%). Their ages ranged from 17 to 105 years (median=78 years). There appeared to be winter excess in hospital admissions, deaths and length of acute hospital stay overall accounting for 3/100,000 extra admissions (winter excess index of 3.4% in men and 7.6% in women) and 1/100,000 deaths (winter excess index of 4.7 and 8.6% in women) due to stroke in winter compared to non-winter periods. Older patients with non-haemorrhagic stroke mainly contribute to this excess. If our findings are replicated throughout England and Wales, it is estimated that there are 1,700 excess admissions, 600 excess in-patient deaths and 24,500 extra acute hospital bed days each winter, related to stroke within the current population of approximately 60 million.

CONCLUSIONS

Further research should be focused on the determinants of winter excess in morbidity and mortality associated with stroke. This may subsequently reduce the morbidity and mortality by providing effective preventive strategies in future.

Exposure-measurement error is frequently ignored when interpreting epidemiologic study results

INTRODUCTION

One important source of error in study results is error in measuring exposures. When interpreting study results, one should consider the impact that exposure-measurement error (EME) might have had on study results.

METHODS

To assess how often this consideration is made and the form it takes, journal articles were randomly sampled from original articles appearing in the American Journal of Epidemiology and Epidemiology in 2001, and the International Journal of Epidemiology between December 2000 and October 2001.

RESULTS

Twenty-two (39%) of the 57 articles surveyed mentioned nothing about EME. Of the 35 articles that mentioned something about EME, 16 articles described qualitatively the effect EME could have had on study results. Only one study quantified the impact of EME on study results; the investigators used a sensitivity analysis. Few authors discussed the measurement error in their study in any detail.

CONCLUSIONS

Overall, the potential impact of EME on error in epidemiologic study results appears to be ignored frequently in practice.

Infradian awake and asleep systolic and diastolic blood pressure rhythms in humans

BACKGROUND

Blood pressure shows 24-h rhythms with a significant seasonal fluctuation.

OBJECTIVES

To characterize 2-month to 12-month infradian rhythms in the mean awake and asleep systolic blood pressure (SBP) and diastolic blood pressure (DBP) in humans.

METHODS

A total of 1689 participants underwent 24-h ambulatory blood pressure monitoring during different periods of the year. The mean daily temperature, humidity, barometric pressure and wind velocity values for the same time span and geographical location were obtained. Fourier analysis was used to fit 12-month, 6-month, 4-month, 3-month and 2-month rhythms to the mean awake and asleep SBP and DBP and to metereological variables.

RESULTS

The awake mean SBP and DBP values showed significant 12-month and 3-month rhythms (respectively, R2 = 55%, P < 0.001 and R2 = 45% P < 0.001), with a peak in July (winter) and a trough-peak difference of 6.2 +/- 1.6 mmHg (P < 0.001, SBP) and 4.2 +/- 1.5 mmHg (P < 0.001, DBP). In contrast, asleep blood pressure means showed mainly 3-month rhythms (SBP, R2 = 19%, P < 0.02; DBP, R2 = 43% P < 0.02). Mean daily temperature and humidity showed at 12-month, 6-month, 4-month, 3-month and 2-month rhythms, barometric pressure showed 12-month and 6-month rhythms, and wind velocity showed 12-month and 3-month rhythms. Minimal temperature values and maximal humidity values coincided with elevated blood pressure values.

CONCLUSION

Awake blood pressure means exhibited mainly circannual fluctuations while asleep blood pressure means showed principally 3-month rhythms. Infradian blood pressure variations correlated with some meteorological variables.

Heat-related and cold-related deaths in England and Wales: who is at risk?

BACKGROUND

Despite the high burden from exposure to both hot and cold weather each year in England and Wales, there has been relatively little investigation on who is most at risk, resulting in uncertainties in informing government interventions.

OBJECTIVE

To determine the subgroups of the population that are most vulnerable to heat-related and cold-related mortality.

METHODS

Ecological time-series study of daily mortality in all regions of England and Wales between 1993 and 2003, with postcode linkage of individual deaths to a UK database of all care and nursing homes, and 2001 UK census small-area indicators.

RESULTS

A risk of mortality was observed for both heat and cold exposure in all regions, with the strongest heat effects in London and strongest cold effects in the Eastern region. For all regions, a mean relative risk of 1.03 (95% confidence interval (CI) 1.02 to 1.03) was estimated per degree increase above the heat threshold, defined as the 95th centile of the temperature distribution in each region, and 1.06 (95% CI 1.05 to 1.06) per degree decrease below the cold threshold (set at the 5th centile). Elderly people, particularly those in nursing and care homes, were most vulnerable. The greatest risk of heat mortality was observed for respiratory and external causes, and in women, which remained after control for age. Vulnerability to either heat or cold was not modified by deprivation, except in rural populations where cold effects were slightly stronger in more deprived areas.

CONCLUSIONS

Interventions to reduce vulnerability to both hot and cold weather should target all elderly people. Specific interventions should also be developed for people in nursing and care homes as heat illness is easily preventable.

CLimate Impacts on Myocardial infarction deaths in the Athens TErritory: the CLIMATE study

OBJECTIVE

To evaluate the impact of meteorological variables on daily and monthly deaths caused by acute myocardial infarction (AMI).

METHODS

All death certificate data from the Athens territory were analysed for AMI deaths in 2001. Daily atmospheric temperature, pressure and relative humidity data were obtained from the National Meteorological Society for Athens for the same year.

RESULTS

The total annual number of deaths caused by AMI was 3126 (1953 men) from a population of 2,664,776 (0.117%). Seasonal variation in deaths was significant, with the average daily AMI deaths in winter being 31.8% higher than in summer (9.89 v 7.35, p < 0.001). Monthly variation was more pronounced for older people (mean daily AMI deaths of people older than 70 years was 3.53 in June and 7.03 in December; p < 0.001) and of only marginal significance for younger people. The best predictor of daily AMI deaths was the average temperature of the previous seven days; the relation between daily AMI deaths and seven-day average temperature (R(2) = 0.109, p < 0.001) was U-shaped. Considering monthly AMI death rates, only mean monthly humidity was independently associated with total deaths from AMI (R(2) = 0.541, p = 0.004).

CONCLUSION

Ambient temperature is an important predictor of AMI mortality even in the mild climate of a Mediterranean city like Athens, its effects being predominantly evident in the elderly. Mean monthly humidity is another meteorological factor that appears to affect monthly numbers of AMI deaths. These findings may be useful for healthcare and civil protection planning.

Seasonality and daily weather conditions in relation to myocardial infarction and sudden cardiac death in Olmsted County, Minnesota, 1979 to 2002

OBJECTIVES

We assessed the relationship of season and weather types with myocardial infarction (MI) and sudden cardiac death (SCD) in a geographically defined population, and tested the hypothesis that the increased risk in winter was related to weather.

BACKGROUND

Winter peaks in coronary heart disease (CHD) have been documented. Yet, it is uncertain if seasonality exists for both incident events and deaths, and the role of weather conditions is not clear.

METHODS

The daily occurrence of incident MI and SCD in Olmsted County was examined with data from the National Weather Service. Poisson regression models were used to assess the relative risks (RRs) associated with season and climatic variables. Subsequent analysis stratified SCD into those with and without antecedent CHD (unexpected SCD).

RESULTS

Between 1979 and 2002, 2,676 MI and 2,066 SCD occurred. The age-, gender-, and year-adjusted RR of SCD, but not of MI, was increased in winter versus summer (1.17, 95% confidence interval [CI] 1.03 to 1.32) and in low temperatures (1.20, 95% CI 1.07 to 1.35, for temperatures below 0 degrees C vs. 18 degrees C to 30 degrees C). These associations were stronger for unexpected SCD than for SCD with prior CHD (p < 0.05). After adjustment for all climatic variables, low temperature was associated with a large increase in the risk of unexpected SCD (RR = 1.38, 95% CI 1.10 to 1.73), while the association with winter declined (RR = 1.06, 95% CI 0.83 to 1.35).

CONCLUSIONS

These data suggest that the winter peak in SCD can be accounted for by daily weather.

Weather-related changes in 24-hour blood pressure profile: effects of age and implications for hypertension management

A downward titration of antihypertensive drug regimens in summertime is often performed on the basis of seasonal variations of clinic blood pressure (BP). However, little is known about the actual interaction between outdoor air temperature and the effects of antihypertensive treatment on ambulatory BP. The combined effects of aging, treatment, and daily mean temperature on clinic and ambulatory BP were investigated in 6404 subjects referred to our units between October 1999 and December 2003. Office and mean 24-hour systolic BP, as well as morning pressure surge, were significantly lower in hot (>90th percentiles of air temperature; 136+/-19, 130+/-14, and 33.3+/-16.1 mm Hg; P<0.05 for all), and higher in cold (<10th percentiles) days (141+/-12, 133+/-11, and 37.3+/-9.5 mm Hg; at least P<0.05 for all) when compared with intermediate days (138+/-18, 132+/-14, and 35.3+/-15.4 mm Hg). At regression analysis, 24-hour and daytime systolic pressure were inversely related to temperature (P<0.01 for all). Conversely, nighttime systolic pressure was positively related to temperature (P<0.02), with hot days being associated with higher nighttime pressure. Air temperature was identified as an independent predictor of nighttime systolic pressure increase in the group of elderly treated hypertensive subjects only. No significant relationship was found between air temperature and heart rate. Our results show for the first time that hot weather is associated with an increase in systolic pressure at night in treated elderly hypertensive subjects. This may be because of a nocturnal BP escape from the effects of a lighter summertime drug regimen and may have important implications for seasonal modulation of antihypertensive treatment.

Seasonal variation in undiagnosed HIV infection on the general medicine and trauma services of two urban hospitals

OBJECTIVE

To examine the seroprevalence of undiagnosed HIV and variation by season among patients admitted to the general internal medicine (GIM) and trauma services of two urban hospitals.

DESIGN

A cross-sectional blinded HIV-1 seroprevalence survey.

SETTING

A 725-bed academic medical center's hospital and an affiliated 324-bed tertiary care hospital.

PARTICIPANTS

Residual serological specimens were obtained for unique patients aged 17 to 65 to study services in summer (June 16 to September 4, 2001) and fall to winter (November 1, 2001 to January 8, 2002).

METHODS

Hospital files provided data on demographics, service type, and discharge clinical categories (fall-winter group only). HIV ELISA (enzyme-linked immunosorbent assay) tests with confirmatory Western blot were linked to subjects' de-identified files. We excluded 34 subjects with known HIV. Of the remaining unique admissions in summer (n=604) and fall-winter (n=978), 60% and 55% were tested, respectively. Predictors of undiagnosed HIV infection were examined using multivariate analysis.

RESULTS

The summer cohort (n=362) had significantly lower unadjusted seroprevalence of undiagnosed HIV infection (1.4%; 95% confidence interval [CI], 0.4% to 3.2%) than the fall-winter cohort (n=539; 3.7%; 95% CI, 2.3% to 5.7%; P=.04). Overall, undiagnosed HIV was somewhat less likely in women (adjusted odds ratio [AOR], 0.45; 95% CI, 0.19 to 1.07) but more likely in black patients (AOR, 3.46; 95% CI, 0.70 to 17.06). In the fall-winter cohort, undiagnosed HIV was more likely for discharges with the following clinical categories versus those with a cardiac condition: dermatologic/breast (AOR, 14.90; 95% CI, 1.20 to 184.77), renal/urological (AOR, 22.43; 95% CI, 2.12 to 236.75), or infectious (AOR, 31.08; 95% CI, 2.40 to 402.98).

CONCLUSIONS

The higher seroprevalence of undiagnosed HIV in the fall-winter admissions to GIM and trauma services supports especially targeting HIV testing in these months.

Seasonal patterns in monthly hemoglobin A1c values

The purpose of this study was to investigate seasonal variations in population monthly hemoglobin A(1c) (A1c) values over 2 years (from October 1998 to September 2000) among US diabetic veterans. The study cohort included 285,705 veterans with 856,181 A1c tests. The authors calculated the monthly average A1c values for the overall population and for subpopulations defined by age, sex, race, insulin use, and climate regions. A1c values were higher in winter and lower in summer with a difference of 0.22. The proportion of A1c values greater than 9.0% followed a similar seasonal pattern that varied from 17.3% to 25.3%. Seasonal autoregressive models including trigonometric function terms were fit to the monthly average A1c values. There were significant seasonal effects; the seasonal variation was consistent across different subpopulations. Regions with colder winter temperatures had larger winter-summer contrasts than did those with warmer winter temperatures. The seasonal patterns followed trends similar to those of many physiologic markers, cardiovascular and other diabetes outcomes, and mortality. These findings have implications for health-care service research in quality-of-care assessment, epidemiologic studies investigating population trends and risk factors, and clinical trials or program evaluations of treatments or interventions.

Vulnerability to winter mortality in elderly people in Britain: population based study

OBJECTIVE

To examine the determinants of vulnerability to winter mortality in elderly British people.

DESIGN

Population based cohort study (119,389 person years of follow up).

SETTING

106 general practices from the Medical Research Council trial of assessment and management of older people in Britain.

PARTICIPANTS

People aged > or = 75 years.

MAIN OUTCOME MEASURES

Mortality (10,123 deaths) determined by follow up through the Office for National Statistics.

RESULTS

Month to month variation accounted for 17% of annual all cause mortality, but only 7.8% after adjustment for temperature. The overall winter:non-winter rate ratio was 1.31 (95% confidence interval 1.26 to 1.36). There was little evidence that this ratio varied by geographical region, age, or any of the personal, socioeconomic, or clinical factors examined, with two exceptions: after adjustment for all major covariates the winter:non-winter ratio in women compared with men was 1.11 (1.00 to 1.23), and those with a self reported history of respiratory illness had a winter:non-winter ratio of 1.20 (1.08 to 1.34) times that of people without a history of respiratory illness. There was no evidence that socioeconomic deprivation or self reported financial worries were predictive of winter death.

CONCLUSION

Except for female sex and pre-existing respiratory illness, there was little evidence for vulnerability to winter death associated with factors thought to lead to vulnerability. The lack of socioeconomic gradient suggests that policies aimed at relief of fuel poverty may need to be supplemented by additional measures to tackle the burden of excess winter deaths in elderly people.

Seasonal variation in diagnoses and visits to family physicians

BACKGROUND

Practice-based research networks (PBRNs) replicating the National Ambulatory Medical Care Survey (NAMCS) must sample more than 1 year to account for presumed seasonal variation in illnesses. This study evaluated the effects of seasonality on diagnoses within NAMCS family physician data.

METHODS

Using combined data from the 1995-1998 NAMCS, diagnostic clusters that accounted for more than 1% of total visits were analyzed for seasonality. Seasons were coded categorically as dummy variables with summer as the reference category. A logistic regression was performed with each diagnosis as an outcome on the full data. To examine the ability of alternative sampling strategies to replicate the full year of data, a simulation study was carried out drawing 50 samples of 1,000 visits each for winter-summer and spring-fall sampling periods.

RESULTS

We found 23 diagnostic clusters that had a frequency more than 1%, of which 10 had seasonal variations (P < or = .001), primarily between winter and summer. If sampling were restricted to spring, the diagnostic clusters of pregnancy and coronary artery disease would account for less than 1% of visits. All other diagnostic clusters, though changing rank order, would account for more than 1% if sampled in a single quarter. In the simulated sampling strategy, visit prevalence dropped below 1% for at least 1 diagnosis in 24 of 50 samples in spring-fall compared with 20 of 50 samples for winter-summer (P > .20).

CONCLUSIONS

There is little seasonal variation in the 23 diagnoses that occur in more than 1% of visits to family physicians. There is, however, important seasonal variation in the rank order of these diagnoses. A sampling strategy that uses any quarter of the year but spring (March, April, May) could be used to understand what diagnoses are frequently seen within a PBRN.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.