Risk factors and clusters of Highly Pathogenic Avian Influenza H5N1 outbreaks in Bangladesh.

Between March 2007 and July 2009, 325 Highly Pathogenic Avian Influenza (HPAI, subtype H5N1) outbreaks in poultry were reported in 154 out of a total of 486 sub-districts in Bangladesh. This study analyzed the temporal and spatial patterns of HPAI H5N1 outbreaks and quantified the relationship between several spatial risk factors and HPAI outbreaks in sub-districts in Bangladesh. We assessed spatial autocorrelation and spatial dependence, and identified clustering sub-districts with disease statistically similar to or dissimilar from their neighbors. Three significant risk factors associated to HPAI H5N1 virus outbreaks were identified; the quadratic log-transformation of human population density [humans per square kilometer, P=0.01, OR 1.15 (95% CI: 1.03-1.28)], the log-transformation of the total commercial poultry population [number of commercial poultry per sub-district, P<0.002, OR 1.40 (95% CI: 1.12-1.74)], and the number of roads per sub-district [P=0.02, OR 1.07 (95% CI: 1.01-1.14)]. The distinct clusters of HPAI outbreaks and risk factors identified could assist the Government of Bangladesh to target surveillance and to concentrate response efforts in areas where disease is likely to occur. Concentrating response efforts may help to combat HPAI more effectively, reducing the environmental viral load and so reducing the number of disease incidents.