Seasonality and Coronary Heart Disease Deaths in United States Firefighters

Abstract

United States firefighters have a high on-duty fatality rate and coronary heart disease is the leading cause. Seasonality affects the incidence of cardiovascular events in the general population, but its effects on firefighters are unknown. We statistically examined the seasonal and annual variation of all on-duty coronary heart disease deaths among US firefighters between 1994 and 2004 using the chi-square distribution and Poisson regression model of the monthly fatality counts. We also examined the effect of ambient temperature (apparent as well as wind chill temperature) on coronary heart disease fatalities during the study span using a time-stratified, case-crossover study design. When grouped by season, we observed the distribution of the 449 coronary heart disease fatalities to show a relative peak in winter (32%) and relative nadir in spring (21%). This pattern was significantly different (p=0.005) from the expected distribution under the null hypothesis where season has no effect. The pattern persisted in additional analyses, stratifying the deaths by the type of duty in which the firefighters were engaged at the time of their deaths. In the Poisson regression model of the monthly fatality counts, the overall goodness-of-fit between the actual and predicted case counts was excellent ( = 16.63; p = 0.002). Two distinct peaks were detected, one in January-February and the other in August-September. Overall, temperature was not associated with increased risk of on-duty death. After allowing for different effects of temperature in mild/hot versus cold periods, a 1°C increase was not protective in cold weather, nor did it increase the risk of death in warmer weather. The findings of this study reveal statistical evidence for excess coronary heart disease deaths among firefighters during winter; however, the temporal pattern coronary heart disease deaths was not linked to temperature variation. We also found the seasonal pattern to be independent of duty-related risks.

Summer outdoor temperature and occupational heat-related illnesses in Quebec (Canada)

“…These results cannot be directly compared to the risk functions developed to quantify the association between outdoor heat and mortality (Mbanu et al, 2007;Mirabelli and Richardson, 2005), because our model was developed essentially on non-fatal heat illnesses (6 fatalities for 259 heat illnesses). Comparison of our results with those of studies on morbidity performed in other latitudes may also be difficult, as hot temperature thresholds for morbidity appear to vary by location (Ye et al, 2012).…”

“…The risk function for the association between average summer temperatures and the number of occupational heat-related deaths was estimated in two studies; in the United States, the risk of on-duty coronary heart disease mortality among firefighters was not associated with increasing temperatures during months with average temperatures above 5 1C, between 1994 and 2004 (Mbanu et al, 2007), while in the whole working population of North Carolina between 1977 and 2001, the rate of heat-related death increased by 37% for each 1 1F increase (corresponding to approximately 77% per 1 1C increase) in average summer temperatures (Mirabelli and Richardson, 2005). In addition, only one pilot study, carried out by the Florida Department of Health (2012) between 2005 and 2009, reported a quantitative relationship between average summer temperatures and heat-related hospitalizations and emergency department visits, where cases were stratified in occupational and non-occupational groups.…”

Mortality and cancer incidence in a cohort of male paid Australian firefighters

“…There is evidence of an association between firefighting and death from cardiovascular disease,15 16 and evidence of an increase in cardiac mortality particularly close to an alarm or turn-out 9 16 17…”

Ethical and Methodological Standards for Laboratory and Medical Biological Rhythm Research

“…Attention should be paid also to the potential role of climate and latitude as possible synchronizers or sources of masking effects, especially in the conduct of chronoepidemiological and seasonality studies (Arendt, 2006;Higuchi et al, 2007;Mbanu et al, 2007;Radun & Radun, 2006;Shah et al, 2006). Papers entailing shift-work research must also clearly define the work schedule and duties of the workers (e.g., Camerino et al, 2008;Eriksen et al, 2006;Jay et al, 2006;Lammers-van der Holst et al, 2006;Persson et al, 2006;Thorne et al, 2008).…”