AbstractDuring surveillance for pneumonia of unknown etiology and sentinel hospital–based surveillance in Beijing, China, we detected avian influenza A(H7N9) virus infection in 4 persons who had pneumonia, influenza-like illness, or asymptomatic infections. Samples from poultry workers, associated poultry environments, and wild birds suggest that this virus might not be present in Beijing.
The first patient infected with influenza A(H7N9) virus in Beijing was found by surveillance for pneumonia of unknown etiology, which was initially designed for finding patients with severe acute respiratory syndrome or influenza A(H5N1) virus infection. Although hospital-based surveillance is less efficient in finding mild and asymptomatic infections, it may be the most feasible approach for identifying severe cases of infection with influenza A(H7N9) virus.
The second patient infected with influenza A(H7N9) virus, the 6-year-old boy, was found through sentinel hospital and laboratory-based surveillance. Before emergence of influenza A(H7N9) virus, surveillance was conducted by using cell culture–based virus isolation techniques. To increase assay sensitivity and rapidity, real-time PCR preceding virus isolation was adopted to replace the strategy of only using virus isolation. In addition, because only specimens positive for seasonal influenza viruses were subjected to virus isolation, this procedure could help avoid the risk for propagating influenza A(H7N9) virus from unknown specimens, as is caused by conducting virus isolation directly in biosafety level 2 laboratories. Our findings and those of another report (8) demonstrated that patients infected with influenza A(H7N9) virus only had ILI. Therefore, the strategy of PCR preceding virus isolation should be the preferred option during sentinel hospital and laboratory-based surveillance.
Live poultry is the major source of avian influenza A(H7N9) (6, 9–11). In addition, migratory birds may participate in multiple reassortment events for emergence of H7N9 subtype virus (1,12). Therefore, the role of wild birds in transmission of avian influenza A(H7N9) virus to poultry or humans should not be ignored. In our samples from poultry workers, associated poultry environments, and wild birds, influenza A(H7N9) virus was not found, which suggests that this virus might not be present in Beijing.
In conclusion, human infections with H7N9 virus can cause a wide spectrum of clinical illnesses. Surveillance of patients with pneumonia of unknown etiology is preferred for early detection of severe cases. PCR is recommended for screening in sentinel hospital and laboratory-based surveillance of influenza A(H7N9).
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