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Environ Health. 2012 Oct 1;11:74. doi: 10.1186/1476-069X-11-74.

Influenza epidemics, seasonality, and the effects of cold weather on cardiac mortality.

Author information

1
Department of Environmental Health, Exposure Epidemiology and Risk Program, Harvard School of Public Health, Boston, MA, USA.

Abstract

BACKGROUND:

More people die in the winter from cardiac disease, and there are competing hypotheses to explain this. The authors conducted a study in 48 US cities to determine how much of the seasonal pattern in cardiac deaths could be explained by influenza epidemics, whether that allowed a more parsimonious control for season than traditional spline models, and whether such control changed the short term association with temperature.

METHODS:

The authors obtained counts of daily cardiac deaths and of emergency hospital admissions of the elderly for influenza during 1992-2000. Quasi-Poisson regression models were conducted estimating the association between daily cardiac mortality, and temperature.

RESULTS:

Controlling for influenza admissions provided a more parsimonious model with better Generalized Cross-Validation, lower residual serial correlation, and better captured Winter peaks. The temperature-response function was not greatly affected by adjusting for influenza. The pooled estimated increase in risk for a temperature decrease from 0 to -5°C was 1.6% (95% confidence interval (CI) 1.1-2.1%). Influenza accounted for 2.3% of cardiac deaths over this period.

CONCLUSIONS:

The results suggest that including epidemic data explained most of the irregular seasonal pattern (about 18% of the total seasonal variation), allowing more parsimonious models than when adjusting for seasonality only with smooth functions of time. The effect of cold temperature is not confounded by epidemics.

PMID:
23025494
PMCID:
PMC3517521
DOI:
10.1186/1476-069X-11-74
[Indexed for MEDLINE]
Free PMC Article

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