Estimates of meteorological variability in association with dengue cases in a coastal city in northern Vietnam: an ecological study

Background Dengue fever (DF) is a vector-borne disease that is sensitive to weather and climate variability. To date, however, this relationship in coastal northern Vietnam has not been well documented. Objectives This paper aims to examine the associations between meteorological variables and dengue incidence in Haiphong, Vietnam, over the period 2008-2012. Methods Monthly data on dengue incidence from all commune health stations and hospitals of Haiphong (with a total population of ~1.8 million) were obtained in accordance with the WHO's recommendations over a 5-year period (2008-2012). Temperature, rainfall, and humidity were recorded as monthly averages by local meteorological stations. The association between ecologic weather variables and dengue cases was assessed using a Poisson regression model. The estimation of regression parameters was based on the method of maximum likelihood using the R program package. Results From 2008 through 2012, 507 cases of dengue were reported. The risk of dengue was increased by sevenfold during the September-December period compared with other months over the period 2008-2012. DF cases in Haiphong were correlated with rainfall and humidity. In the multivariable Poisson regression model, an increased risk of dengue was independently associated with months with a higher amount of rainfall (RR=1.06; 95% CI 1.00-1.13 per 50 mm increase) and higher humidity (RR=1.05; 95% CI 1.02-1.08 per 1% increase). Conclusion These data suggest that rainfall and relative humidity could be used as ecological indicators of dengue risk in Haiphong. Intensified surveillance and disease control during periods with high rainfall and humidity are recommended. This study may provide baseline information for identifying potential long-term effects and adaptation needs of global climate change on dengue in the coming decades.