CDC Reports Influenza A(H7N9) Developments Over Four Annual Epidemics

December 16, 2016 — A new collaborative study between the Chinese Center for Disease Control and Prevention (China CDC) and the U.S. CDC examining the four annual epidemics of avian influenza A(H7N9) that have occurred in China since 2013 reports the expansion of the geographic area of China affected by these viruses and an increase in the proportion of people who are infected with these viruses who become severely ill. The report also notes that an increasing proportion of A(H7N9) viruses are showing genetic changes that may be associated with increased transmission to people. Avian influenza A(H7N9), which was first documented in people in 2013, is estimated to have the greatest potential to cause a pandemic as well as the greatest potential public health impact according to CDC’s influenza risk assessment tool. The CDC report notes that while person-to-person spread of A(H7N9) viruses has not increased and there have been no major changes in the epidemiology associated with A(H7N9) epidemics, recent developments underscore the importance of ongoing rigorous efforts to check this threat to the global community.  

Since the China CDC reported the first case of influenza A(H7N9) virus infection in a person in 2013, there have been roughly 775 laboratory-confirmed infections in people in mainland China. Twenty-three additional infections and four deaths were in visitors to mainland China. Most people infected with A(H7N9) virus have experienced severe respiratory illness, with about one-third of infections resulting in death.

The four epidemics shared some similar characteristics, including age and gender distribution of patients, and history of exposure (primarily to live poultry within the two weeks prior to illness). However, the most recent epidemic (Sept. 2015 – Aug. 2016) demonstrated some notable differences from the first three.

According to the CDC report, during the fourth epidemic:

• Infections were reported from areas of China where none had been previously reported.
• More infections were being reported in people living in rural areas. In the fourth epidemic, more infected people reported living in rural areas than in the first three epidemics combined.
• Infected people were significantly more likely to develop pneumonia and be admitted to the intensive care unit (although not more likely to die).
• Laboratory analysis of viruses found a growing proportion of A(H7N9) viruses had genetic changes that might enhance the ability for A(H7N9) viruses to spread to people.
• The most recent outbreak lasted longer than the previous three epidemics.

The potential pandemic risk of influenza A(H7N9) was assessed by using CDC’s Influenza Risk Assessment Tool (IRAT). The IRAT is an evaluation tool developed by CDC and external influenza experts that assesses the potential pandemic risk posed by influenza A viruses that currently circulate in animals, but not in humans.

CDC recommendations for travelers to China have been in place since 2013. This includes recommendations to not touch birds or other animals and wash hands often. Poultry and poultry products should be fully cooked. CDC will update its advice for travelers if the situation in China changes. This guidance is available at Avian Flu (H7N9) in China.

Read the full report here.

CDC has created an Avian Influenza microsite (https://tools.cdc.gov/medialibrary) an easily embeddable collection of information that can supplement a website with CDC content. The microsite will automatically updated in real time as CDC updates its content. For instructions on how to get the Avian Influenza microsite and for technical support, visit the CDC Public Health Media Library at: https://tools.cdc.gov/medialibrary.