Abstract
BackgroundInfluenza peaks during the wintertime in temperate regions and during the annual rainy season in tropical regions – however reasons for the observed differences in disease ecology are poorly understood. We hypothesize that episodes of extreme precipitation also result in increased influenza in the Northeastern United States, but this association is not readily apparent, as no defined ‘rainy season’ occurs. Our objective was to evaluate the association between extreme precipitation (≥ 99th percentile) events and risk of emergency room (ER) visit for influenza in Massachusetts during 2002–2008.MethodsA case-crossover analysis of extreme precipitation events and influenza ER visits was conducted using hospital administrative data including patient town of residence, date of visit, age, sex, and associated diagnostic codes. Daily precipitation estimates were generated for each town based upon data from the National Oceanic and Atmospheric Administration. Odds ratio (OR) and 95% confidence intervals (CI) for associations between extreme precipitation and ER visits for influenza were estimated using conditional logistic regression.ResultsExtreme precipitation events were associated with an OR = 1.23 (95%CI: 1.16, 1.30) for ER visits for influenza at lag days 0–6. There was significant effect modification by race, with the strongest association observed among Blacks (OR = 1.48 (1.30, 1.68)).ConclusionsWe observed a positive association between extreme precipitation events and ER visits for influenza, particularly among Blacks. Our results suggest that influenza is associated with extreme precipitation in a temperate area; this association could be a result of disease ecology, behavioral changes such as indoor crowding, or both. Extreme precipitation events are expected to increase in the Northeastern United States as climate change progresses. Additional research exploring the basis of this association can inform potential interventions for extreme weather events and influenza transmission.
Highlights
Influenza peaks during the wintertime in temperate regions and during the annual rainy season in tropical regions – reasons for the observed differences in disease ecology are poorly understood
Our goal was to study the association between extreme precipitation and emergency room (ER) visits for influenza among people living in a temperate climate
Environmental data Daily precipitation estimates were generated for each town in MA based upon the National Oceanic and Atmospheric Administration (NOAA)-generated 4 × 4 km grid of daily precipitation estimates during 2002–2008 [17]
Summary
Influenza peaks during the wintertime in temperate regions and during the annual rainy season in tropical regions – reasons for the observed differences in disease ecology are poorly understood. In tropical climates, acute respiratory infections, including influenza, peak. A seasonal analysis of influenza surveillance conducted in India from 1978 to 1990 observed a positive association (r = 0.697, p < 0.05) with rainfall [13]. In later years (2007–2008), a 24 month study comparing throat and nasal swabs from young children in India found a strong positive correlation between influenza A virus and rainfall (r = 0.901, p < 0.0001) as well [10]. Additional studies observed positive, but not statistically significant, associations between rainfall and influenza in infants and children [12, 14]
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