By Stan Deresinski, MD, FACP, FIDSA, Clinical Professor of Medicine, Stanford University, Hospital Epidemiologist, Sequoia Hospital, Redwood City, CA, Editor of Infectious Disease Alert.

Sources: World Health Organization. Global Alert and Response. Human infection with avian influenza A (H7N9) virus in China – update.

Centers for Disease Control and Prevention. CDC Health Advisory. Human infections with novel influenza A (H7N9) viruses.

A novel avian influenza A virus, H7N9, had caused, as of 18 April 2013, 87 laboratory confirmed cases of human infection, with the first case having an onset of illness on February 19. H7N9 had never previously been demonstrated to infect any mammalian species. The cases occurred in 4 adjacent provinces of China: Henan, Jiangsu, Zhejiang, and Anhui, as well as in Shanghai Beijing municipalities. Shanghai and Zhejiang together have accounted 59 cases and 13 deaths. The fact that infected avians generally appear well together with the recent observation of asymptomatic human infection complicates surveillance efforts.

To date, there has been no clear evidence of human-to-human transmission, although familial occurrence has been observed and hundreds of close contacts of confirmed cases are being closely monitored. Some cases have had no known direct contact with avians. The virus appears to be susceptible to neuraminidase inhibitors, but resistant to the adamantanes.

Other avian influenza viruses have recently caused human disease. The highly pathogenic avian influenza A (H7N3) virus in Jalisco, Mexico caused illness in 2 poultry workers in 2012. H5N1, a highly pathogenic avian virus, has caused human disease in Egypt and several Asian countries. Other novel viruses have been associated with swine contact as in 16 individuals who developed H3N2v infection in the U.S. in the summer of 2012.

Examination of the gene sequences of the first 3 isolated viruses indicate changes seen in viral strains with high virulence in mammals. The virus is a triple assortment with all genes of avian origin 1. As a “novel,” i.e., a “non-human” virus, H7N9 has the potential to cause a pandemic in a virgin human population — if it acquires the capacity for facile human-to-human transmission.

China reported slaughtering 20,358 birds in response to detection of the virus in pigeons in the Huhai live bird market in Shanghai. The Centers for Disease Control and Prevention has started the process of making a seed virus in anticipation of the possible need for vaccine production.

The CDC can provide testing for novel influenza A (H7N9) virus infection, and is also developing a test kit for use by state laboratories. At this time, no human cases of H7N9 have been detected in the United States. Clinicians should consider the possibility of H7N9 virus infection in persons with respiratory illness who also meet either of the exposure criteria below:

• Patients with recent travel to countries where human cases of novel H7N9 virus infection have recently been detected, especially if there was recent direct or close contact with animals (such as wild birds, poultry, or pigs) or where H7N9 viruses are known to be circulating in animals. Currently, China is the only country that has recently reported novel H7N9 human cases.

• Patients who have had recent contact with confirmed human cases of infection with novel H7N9 virus.


1. Gao R, et al. Human Infection with a Novel Avian-Origin Influenza A (H7N9) Virus. N Engl J Med 2013 Apr 11. [Epub ahead of print]