Epidemiology of avian influenza A H7N9 virus in human beings across five epidemics in mainland China, 2013–17: an epidemiological study of laboratory-confirmed case series

Abstract

SUMMARY Background Avian influenza A(H7N9) virus has caused human infections in China since 2013, and a large epidemic in 2016–17 has prompted concerns of whether the epidemiology has changed to suggest an increasing pandemic threat. Our study aimed to describe the epidemiological characteristics, clinical severity, and time-to-event distributions of A(H7N9) case-patients in the 2016–17 epidemic wave compared with previous waves. Methods We obtained information about all laboratory-confirmed human cases of A(H7N9) virus infection reported in mainland China as of 23 February 2017. We described the epidemiological characteristics across epidemic waves, and estimated the risk for death, mechanical ventilation, and admission to the intensive care unit for patients who required hospitalization for medical reasons. We estimated the incubation periods, and time delays from illness onset to hospital admission, illness onset to initiation of antiviral treatment, and hospital admission to death or discharge. Findings The 2016–17 A(H7N9) epidemic wave began earlier, spread to more counties in affected provinces and had more confirmed cases than previous epidemic waves. There was an increase in the proportion of cases in middle-aged adults and in semi-urban and rural residents. The clinical severity of hospitalized cases in 2016–17 was comparable to the previous epidemic waves. Interpretation Age distribution and case sources changed gradually across epidemic waves, while clinical severity has not changed substantially. Continued vigilance and sustained intensive control efforts are needed to minimize the risk of human infection with A(H7N9) virus. Funding The National Science Fund for Distinguished Young Scholars (grant no. 81525023).

Comparison of the three waves of avian influenza A(H7N9) virus circulation since live poultry markets were permanently closed in the main urban areas in Zhejiang Province, July 2014‐June 2017

“…Our study also demonstrated that the demographic characteristics and exposure patterns of H7N9 cases had no significant changes during the most recent waves. However, there was a wide geographic distribution of cases as well as new occurring districts/counties in the fifth epidemic comparing with the third and fourth waves, which was also consistent to the above‐mentioned studies 9, 10, 18. Moreover, despite the wide geographic coverage of cases in the fifth wave, the larger proportion of them actually occurred in the non‐LPMs closure areas.…”

“…The national study showed that the main epidemiological characteristics remained unchanged 9, 10. Another study conducted in Jiangsu province, the most impacted province in China in the fifth wave, also reached similar conclusions 18.…”

“…However, our study showed that although rural cases still account for majority of the total count, there is not enough evidence to suggest an increasing trend during the latest three waves. Recently, a national study showed that more cases shifted from urban locations to semi‐urban and rural areas 10. However,as the definition for rural and urban cases differed in our study, we were not able to make a direct comparison.…”

“…To control its impact, temporary or permanent closure of live poultry markets has been implemented by many local governments, leading to a declining trend of laboratory‐confirmed cases in the first four waves 7, 8, 9, 10, 11. However, an unprecedented outbreak of human infection with avian influenza A(H7N9) virus, identified as the fifth wave, occurred in China from September 2016, and a number of cases reported in the fifth wave exceeded those reported in the previous waves in China 8, 9, 10, 12…”

Potency determination of inactivated H7 influenza vaccines using monoclonal antibody‐based ELISA and biolayer interferometry assays

“…Since the initial outbreak, waves of A(H7N9) virus infections in humans have reappeared each winter season, resulting in numerous human infections and deaths 25. We generated and characterized several mAbs recognizing different epitopes on the H7 HA and evaluated these mAbs, as well as H7 mAbs (mAbs 62 and 98) that were developed several years prior to the A(H7N9) outbreak in China, for potency determination of A(H7N9) vaccines using two assay formats.…”