Assessing Change in Avian Influenza A(H7N9) Virus Infections During the Fourth Epidemic — China, September 2015–August 2016

Abstract

© 2016, Department of Health and Human Services. All rights reserved. What is already known about this topic? Influenza A(H7N9) virus is a low pathogenic avian influenza virus that can cause severe illness in humans, with a case-fatal­ity rate of 40%. Since March 2013, China has experienced four annual avian influenza A(H7N9) virus epidemics with human infections. Most human infections have been associated with exposure to live poultry, particularly in live-poultry markets. In the first three annual epidemics, there was no evidence of sustained human-to-human transmission. What is added by this report? Epidemiology and virology data from the most recent (fourth) epidemic, September 2015–August 2016, suggest no evidence of increased transmissibility of A(H7N9) virus from poultry or environmental exposures to humans or of sustained human-to-human transmission. Characteristics of the fourth epidemic included greater percentages of patients admitted to intensive care units and with diagnoses of pneumonia, identification of the virus in new areas, a greater percentage of infected persons living in rural areas, and a longer epidemic period. Genetic changes in the virus have not been sufficient to alter antigenic properties or cause mismatch with candidate vaccines. What are the implications for public health practice? There is a need for a national containment-control-eradication program in poultry, in addition to effective A(H7N9) virus surveillance and continued risk assessment among humans and poultry in China and neighboring countries.