Risk Factors for Human Infection with H7N9

A study by CDC and China CDC has identified specific risk factors and exposure risks for human infections with the avian influenza A (H7N9) virus. Key findings showed that exposure to poultry in live bird markets was the primary source of H7N9 infections among people in China. Merely being in a location with poultry was significantly associated with increased risk of H7N9 infection. Many cases were only exposed to a market once in the period when they were likely infected.  However, raising poultry at home and consumption of poultry were not associated with an increased risk of H7N9 illness. Underlying health conditions that were significantly associated with H7N9 infections in China included obesity, chronic obstructive pulmonary disease (COPD), and being on immunosuppressive medications.

This study was conducted from April to June 2013 in eight Chinese provinces and used a case-control design. Researchers analyzed data from 89 patients with laboratory-confirmed H7N9 infection and 339 controls. Controls were people in China that were matched to cases by age, sex and neighborhood.