Investigation of Highly Pathogenic Avian Influenza (H5N1) Outbreaks among Poultry in Ningxia, China, 2012

In April 2012, there were reports of suspected highly pathogenic avian influenza (HPAI) H5N1 among poultry layers in Ningxia. A retrospective investigation was conducted to describe epidemiological characteristics of the outbreak and identify risk factors for HPAI H5N1 infection. We administered a questionnaire to all 87 poultry layer farms in Touying County, Ningxia Province, within four weeks following the last reported outbreak. Samples of sick chickens were collected from 45 suspected farms to determine presence of H5N1 virus by reverse transcription polymerase chain reaction (RT-PCR) and confirmed by virus isolation. We used multiple logistic regression analysis to identify risk factors for infection and semivariogram analysis to demonstrate clustering of infected farms. Among 45 farms with positive PCR results, virus was isolated from four farms. Farms with improper waste disposal (Adjusted OR = 2.7, 95% CI = 1.20-8.30) and having visitors in farm within the past month (OR = 5.5, 95% CI = 1.97-15.64) were significantly associated with HPAI infection. H5N1 was widespread in the county. Frequent human movement into farms and improper waste management increased the risk of infection. Biosecurity practices, including limiting number of visitors and proper waste disposal, should be enhanced to prevent further H5N1 infection.