A prospective study was conducted from November 2013 to February 2014 to estimate the spatial clustering; cumulative incidence and risk factors associated with avian influenza (AI) subtype H9 infection on commercial poultry farms of Pakistan. A total of 400 farms were enrolled and followed during the study period. Among these, 109 farms submitted samples suspected for AI to the laboratory, and only 47 farms were confirmed positive by hemagglutinin inhibition (HI) test. Data was collected from these 109 farms about their demography, management, and biosecurity practices. The cumulative incidence of H9N2 was 11.75 % (95 % confidence interval (CI) 8.76-15.23). The highest number of cases (40.42 %) was reported in January. One most likely cluster (p = 0.009, radius = 4.61 km) occurred in the Kasur district. Multivariable logistic regression analyses showed that the presence of wild birds on the farms (odds ratio (OR) = 16.18; 95 % CI 3.94-66.45) was independently associated with H9N2 infection. Cleaning of cages before delivery on farm (OR = 0.16; 95 % CI = 0.06-0.47), presence of a footbath at the entrance of farm (OR = 0.24; 95 % CI 0.08-0.79), and changing of gloves (OR = 0.33; 95 % CI 0.11-0.99) were protective factors against H9N2 infection. Reducing the exposure to risk factors and adapting biosecurity measures may reduce the risk of AI H9N2 infection on commercial poultry farms in Pakistan.
Keywords: Attack rate; Avian influenza; Commercial poultry farms; H9N2 serotype; Prospective study; Zoonosis.