Clinical severity of human infections with avian influenza A(H7N9) virus, China, 2013/14

Area of Science:

• Epidemiology
• Infectious Diseases
• Public Health

Background:

• Emerging infectious diseases pose challenges in severity assessment due to potential ascertainment biases.
• The influenza A(H7N9) virus caused two epidemic waves in China, starting in March 2013.
• Laboratory-confirmed cases were identified during both epidemic waves.

Purpose of the Study:

• To assess and compare the severity of human infections with influenza A(H7N9) virus across two epidemic waves in China.
• To estimate the risk of death among hospitalized and symptomatic cases during the second epidemic wave.

Main Methods:

• Utilized data from laboratory-confirmed cases and national sentinel influenza-like illness surveillance.
• Estimated risk of death for hospitalized and symptomatic cases during the second wave (October 2013-October 2014).
• Compared findings with estimates from the first wave (January-September 2013).

Main Results:

• The estimated risk of death among hospitalized influenza A(H7N9) cases was 48% in the second wave, higher than in the first wave.
• Age-specific risks of death were also significantly higher in hospitalized cases during the second wave.
• The estimated risk of death among symptomatic influenza A(H7N9) cases was 0.10% in the second wave, similar to the first wave.

Conclusions:

• A potential increase in mortality among hospitalized cases during the second wave warrants further investigation into viral changes, host factors, or treatment variations.
• The risk of death among symptomatic influenza A(H7N9) cases remained consistently low across both epidemic waves.
• Ascertainment biases may influence the observed increase in mortality risk among hospitalized cases in the second wave.