Comparison of the first three waves of avian influenza A(H7N9) virus circulation in the mainland of the People’s Republic of China

Abstract

BackgroundH7N9 human cases were first detected in mainland China in March 2013. Circulation of this virus has continued each year shifting to typical winter months. We compared the clinical and epidemiologic characteristics for the first three waves of virus circulation.MethodsThe first wave was defined as reported cases with onset dates between March 31-September 30, 2013, the second wave was defined as October 1, 2013-September 30, 2014 and the third wave was defined as October 1, 2014-September 30, 2015. We used simple descriptive statistics to compare characteristics of the three distinct waves of virus circulation.ResultsIn mainland China, 134 cases, 306 cases and 219 cases were detected and reported in first three waves, respectively. The median age of cases was statistically significantly older in the first wave (61 years vs. 56 years, 56 years, p < 0.001) compared to the following two waves. Most reported cases were among men in all three waves. There was no statistically significant difference between case fatality proportions (33, 42 and 45%, respectively, p = 0.08). There were no significant statistical differences for time from illness onset to first seeking healthcare, hospitalization, lab confirmation, initiation antiviral treatment and death between the three waves. A similar percentage of cases in all waves reported exposure to poultry or live poultry markets (87%, 88%, 90%, respectively). There was no statistically significant difference in the occurrence of severe disease between the each of the first three waves of virus circulation. Twenty-one clusters were reported during these three waves (4, 11 and 6 clusters, respectively), of which, 14 were considered to be possible human-to-human transmission.ConclusionThough our case investigation for the first three waves found few differences between the epidemiologic and clinical characteristics, there is continued international concern about the pandemic potential of this virus. Since the virus continues to circulate, causes more severe disease, has the ability to mutate and become transmissible from human-to-human, and there is limited natural protection from infection in communities, it is critical that surveillance systems in China and elsewhere are alert to the influenza H7N9 virus.

Sudden increase in human infection with avian influenza A(H7N9) virus in China, September–December 2016

“…Regardless, the demographic characteristics of cases, such as age and sex distribution and exposure history in the fifth epidemic, were similar to those in earlier epidemics. ( 2 , 3 ) Consistent with a prior report, ( 10 ) elderly people, especially those with underlying medical conditions, remain the most vulnerable population.…”

“…Studies have shown that the demographic, epidemiologic and virologic characteristics of H7N9 cases from these epidemics remained unchanged, while the epidemic curve illustrated a decline in the magnitude of outbreaks over time, particularly in the third and fourth seasons in 2015 and 2016. ( 2 , 3 ) However, since September 2016, not only has the fifth outbreak started earlier than usual, but a steep increase in the number of humans infected with H7N9 virus has also been observed, causing domestic and international concern. On 9 January 2017, China notified the World Health Organization through the International Health Regulations mechanism of 106 cases.…”

Assessing Change in Avian Influenza A(H7N9) Virus Infections During the Fourth Epidemic — China, September 2015–August 2016

“…Prior investigations demonstrated that age and sex distribution, clinical features, and exposure history of A(H7N9) virus human infections reported during the first three epidemics were similar (2). In this report, epidemiology and virology data from the most recent, fourth epidemic (September 2015-August 2016) were compared with those from the three earlier epidemics.…”

Emerging Infectious Diseases and Blood Safety: Modeling the Transfusion-Transmission Risk

“…While EIDs are not a new phenomenon, the frequency of reported outbreaks has increased in the last 20 years and experts predict that this will continue [17,18,21,26,[28][29][30]. To emphasize this point, the list of 21st century outbreaks already includes, in addition to ongoing outbreaks of West Nile virus (WNV) [31,32], severe acute respiratory syndrome corona virus (SARS-CoV) in China in 2002-3 [33,34], the reemergence of avian influenza virus H5N1 (A(H5N1) [35], chikungunya virus (CHIKV) on La Reunion island in 2005-07 followed by the Western Pacific region in 2012 and the Americas in 2013 [36][37][38][39], influenza A virus H1N1 ((A(H1N1)) [40], Middle East respiratory syndrome corona virus (MERS-CoV) in 2012 in the Middle East [41], influenza A virus H7N9 (A(H7N9)) in 2013 in China [42], ZIKV on Yap Is in 2007, the Western Pacific region in 2014 and the Americas in 2015-16 [43] and Ebola virus (EBOV) in West Africa in 2014-15 [44].…”