Risk for Highly Pathogenic Avian Influenza H5N1 Virus Infection in Chickens in Small‐Scale Commercial Farms,in a High‐Risk Area,Bangladesh, 2008

Small‐scale commercial chicken farms (FAO‐defined system 3) with poor biosecurity predominate in developing countries including Bangladesh. By enroling fifteen highly pathogenic avian influenza (HPAI) cases occurring in such farms – (February – April 2008) and 45 control farms (March–May 2008) with similar set up, we conducted a case–control study to evaluate the risk factors associated with HPAI H5N1 virus infections in chickens reared in small‐scale commercial farms in a spatially high‐risk area in Bangladesh. Data collected by a questionnaire from the selected farms were analysed by univariable analysis and multivariable conditional logistic regression. The risk factors independently associated were ‘dead crow seen at or near farm’ odds ratio (OR) 47.4, 95% confidence interval (CI) 4.7–480.3, P = 0.001], ‘exchanging eggtrays with market vendors’ (OR 20.4, 95% CI 1.9–225.5, P = 0.014) and ‘mortality seen in backyard chicken reared nearby’ (OR 19.4, 95% CI 2.8–131.9, P = 0.002). These observations suggest that improved biosecurity might reduce the occurrence of HPAI outbreaks in small‐scale commercial farms in Bangladesh.