Human infections with avian influenza A H7N9 virus seem to be less serious than previously reported, according to collaborating researchers from the Chinese Center for Disease Control and Prevention, in Beijing and The University of Hong Kong.
Using a combination of data from China’s sentinel surveillance network and estimates on the number of people likely to seek health care after becoming infected, investigators estimate that H7N9 carries a 36% fatality risk for all ages on admission to hospital. This is lower than the fatality risk of the H5N1 strain that emerged in 2003, which had a fatality risk of around 60% for admitted patients, but has a higher fatality risk than the 2009 H1N1 pandemic influenza, which killed 21% of admitted patients.
“Although previous clinical case series have focused on the potential for avian influenza H7N9 virus infection to cause severe illness, we have estimated that mild cases might have occurred. Our results thus support continued vigilance and sustained intensive control efforts against the virus to minimize risk of human infection, which is greater than previously recognized,” the authors wrote.
The research appeared in the current issue of [removed]The Lancet[/removed], along with [removed]a secondary article[/removed] from the same authors that compared the epidemiological characteristics of H7N9 and the older H5N1 viruses.
The team warns that public health officials and health care workers need to be prepared for a possible resurgence of H7N9.
“Although we have reported the fatality risk for patients admitted to hospital, the symptomatic case-fatality risk remains to be established and a large portion of the ‘clinical iceberg’ of infection might have remained undetected so far,” the authors concluded. “If H7N9 follows a similar pattern to H5N1, the epidemic could reappear in the autumn. This potential lull should be an opportunity for discussion of definitive preventive public health measures, optimization of clinical management, and capacity building in the region in view of the possibility that H7N9 could spread beyond China’s borders.”