Evaluation of risk factors for the spread of low pathogenicity H7N2 avian influenza virus among commercial poultry farms

Objective - To identify risk factors associated with the spread of low pathogenicity H7N2 avian influenza (AI) virus among commercial poultry farms in western Virginia during an outbreak in 2002. Design - Case-control study. Procedure - Questionnaires were used to collect information out farm characteristics, biosecurity rneasures, and husbandry practices on 151 infected premises (128 turkey and 23 chicken farms) and 199 noninfected premises (167 turkey and 32 chicken farms). Results - The most significant risk factor for AI infection was disposal of dead birds by rendering (odds ratio [OR] 73). In addition, age greater than or equal to 10 weeks (OR for birds aged 10 to 19 weeks, 4.9; OR for birds aged greater than or equal to 20 weeks, 4.3) was a significant risk factor regardless of poultry species involved. Other significant risk factors included use of nonfamily caretakers and the presence of mammalian wildlife on the farm. Factors that were not significantly associated with infection included use of various routine biosecurity measures, food and litter sources, types of domestic animals on the premises, and presence of wild birds on the premises. Conclusions and Clinical Relevance - Results suggest that an important factor contributing to rapid early spread of AI virus infection among commercial poultry farms during this outbreak was disposal of dead birds via rendering off-farm. Because of the highly infectious nature of AI virus and the devastating economic impact of outbreaks, poultry farmers should consider carcass disposal techniques that do not require farm movement, such as burial, composting, or incineration.