Influenza-Like Illness Seasonality and its Association with Meteorological Variations in Dak Lak Province, Vietnam, 2004-2009

Background: Influenza is a global public health and economic burden. Its patterns of seasonality differ considerably between geographic regions, but the factors underlying these differences are not well understood. Clarifying the potential role of climate factors on incidence of influenza could provide an insight into the mechanisms of the seasonality of the disease. This study documents the activity of influenza-like illness (ILI) in Dak Lak province of Vietnam and examines its temporal association with climate factors.

Methods: From 2004 through 2009, monthly ILI episodes were reported from all commune health stations and hospitals in 13 districts of Dak Lak province (total population: ~1.7 million) by national communicable disease surveillance. Temperature, sunshine duration, rainfall and humidity were recorded as monthly averages by local meteorological stations across the province. The association between these climatic factors and ILI was assessed by using a Poisson regression model.

Results: During the study period, 260,556 episodes of ILI were reported. The mean monthly number of ILI cases recorded during the Dak Lak rainy season (July through December) was significantly higher (p<0.01) than that recorded in the dry season (Risk Ratio: 1.17; 95% confidence interval: 1.04-1.31). In a multivariable Poisson regression analysis, an increased risk of ILI was independently associated with higher temperature (Risk Ratio: 1.05; 95% confidence interval: 1.01-1.09 per 1.50C increase in monthly mean temperature).

Conclusions: These data suggest that monthly rainfall and temperature could be used as ecological indicators of ILI risk in the Vietnams Central Highlands region. Intensified surveillance and control of influenza during rainy season periods are recommended. The data also suggest that the occurrence of influenza in the region likely results from multiple causes which remain to be delineated.

Keywords: influenza, influenza-like illness, temperature, seasonality, regression analysis

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Author (s): 

Hau V. Pham1,2, T. Phan1,2, L. Phan2, N. Tran Minh2 1Institute of Hygiene and Epidemiology of Tay Nguyen, Vietnam 2Vietnam Field Epidemiology Training Program

Presenter (s): 
Dr. Hau Pham
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