Asian Lineage Avian Influenza A (H7N9) Virus
Human infections with an Asian lineage avian influenza A (H7N9) virus (Asian H7N9 were first reported in China in March 2013. Annual epidemics of sporadic human infections with Asian H7N9 viruses in China have been reported since that time. China is currently experiencing its 5th epidemic of Asian H7N9 human infections. On February 27, 2017, the World Health Organization (WHO) announced that 460 human infections with Asian H7N9 virus had been reported during the 5th epidemic,[1.3 MB, 15 Pages] making it the largest annual epidemic to date. This brings the total cumulative number of human infections with Asian lineage H7N9 reported by WHO to 1,258. During epidemics one through four, about 40 percent of people confirmed with Asian H7N9 virus infection died.
Most human infections with avian influenza viruses, including Asian H7N9 virus, have occurred after exposure to poultry; Asian H7N9 viruses continue to circulate in poultry in China. Most reported patients with H7N9 virus infection have had severe respiratory illness (e.g., pneumonia). Rare instances of limited person-to-person spread of this virus have been identified in China, but there is no evidence of sustained person-to-person spread. Some human infections with Asian H7N9 have been reported outside of mainland China but most of these infections have occurred among people who had traveled to mainland China before becoming ill. Asian H7N9 viruses have not been detected in people or birds in the United States.
While the current risk to the public's health posed by Asian H7N9 virus is low, the pandemic potential of this virus is concerning. Influenza viruses constantly change and it's possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease (pandemic). In fact, of the novel influenza A viruses that are of special concern to public health, Asian lineage H7N9 virus is rated by the Influenza Risk Assessment Tool (IRAT) as having the greatest potential to cause a pandemic, as well as potentially posing the greatest risk to severely impact public health.
It's likely that sporadic human infections with Asian H7N9 virus associated with poultry exposure will continue to occur in China. It's also possible that Asian H7N9 virus may spread to poultry in neighboring countries and that human infections associated with poultry exposure may be detected in neighboring countries. It's also possible that Asian H7N9 infections may continue to be detected among travelers returning from countries where this virus is present. However, as long as there is no evidence of ongoing, sustained person-to-person spread, the public health risk assessment would not change substantially.