16.12.2016

MMWR: December 16, 2016

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.
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.