Prospective Study of Avian Influenza Infection in Backyard Poultry Flocks and Flock Handlers in Wisconsin

Background: The continuing epizootic of H5N1 avian influenza (AI) in Asia and subsequent zoonotic transmission has led to heightened concerns about a pandemic and the demand for improved surveillance of poultry in all sectors, including backyard poultry. We conducted a 15-month prospective study to determine the prevalence of AI in backyard poultry and extent of transmission to flock handlers. Methods: Starting July 2007, registered poultry owners in six counties in central Wisconsin were mailed invitations to participate; household members with poultry exposure were also invited. Premises with < 1000 birds were eligible. Participants completed a baseline interview to characterize poultry exposures. Illness in flocks and flock handlers was monitored using semimonthly telephone interviews and self-report of acute influenza-like symptoms by flock handlers. Participants provided blood at baseline and at the end of the surveillance period for serology and, if ill, nasopharyngeal, eye, and throat swabs for viral testing. Blood was also collected at baseline from a convenience sample of adult poultry. Results: We enrolled 87 flocks and 128 persons who had regular contact with poultry. Influenza-like symptoms were reported by 77 (65%) persons. Swabs were collected from 53 persons at 88 illness episodes. AI was not isolated, but five persons were positive for human influenza. Twenty-one participants (20%) seroconverted to at least one human influenza strain, but there were no seroconversions to AI. Blood samples from all 717 birds tested were seronegative for influenza. Conclusion: Despite limited biosecurity there was no evidence of AI infection in participating backyard flocks or flock handlers.