Evidence for avian influenza A infections among Iowa's agricultural workers

Background: Identifying risk factors for zoonotic influenza transmission may aid public health officials in pandemic influenza planning. Objectives: We sought to evaluate rural Iowan agriculture workers exposed to poultry for previous evidence of avian influenza virus infection. Methods: In 2004, we enrolled 803 rural adult Iowans in a 2-year prospective study of zoonotic influenza transmission. Their enrollment data and sera were compared with those of 66 adult controls enrolled at the University of Iowa in 2006 by using proportional odds modeling. Results: Of the 803 participants 58.8% were male with a mean age of 55.6 years. Forty-eight percent reported previous poultry exposure. Sera were studied by microneutralization techniques for antibodies against avian H4, H5, H6, H7 and H9 viruses. Touching live birds was associated (OR 1.2; 95% CI 1.2-1.8) with increased antibody titer against H5 virus. Similarly, participants who reported hunting wild birds had increased antibody titers against H7 virus (OR 2.8; 95%CI 1.2-6.5) and subjects who reported recent exposure to poultry had increased antibody titers against H6 (OR 3.4; 95% CI 1.4-8.5) and H7 viruses (OR 2.5, 95% CI 1.1-5.7). There was no evidence of elevated antibody against avian H4 or H9 viruses. Conclusions: These data suggest that hunting and exposure to poultry may be important risk factors for avian influenza virus infection among rural US populations. Agriculture workers should be included in influenza pandemic plans.