Comparative epidemiology of human infections with avian influenza A H7N9 and H5N1 viruses in China: a population-based study of laboratory-confirmed cases

Abstract

Background The novel influenza A(H7N9) virus recently emerged, while influenza A(H5N1) virus has infected humans since 2003 in mainland China. Both infections are thought to be predominantly zoonotic. We compared the epidemiologic characteristics of the complete series of laboratory-confirmed cases of both viruses in mainland China to date. Methods An integrated database was constructed with information on demographic, epidemiological, and clinical variables of laboratory-confirmed A(H7N9) and A(H5N1) cases that were reported to the Chinese Center for Disease Control and Prevention up to May 24, 2013. We described disease occurrence by age, sex and geography and estimated key epidemiologic parameters. Findings Among 130 and 43 patients with confirmed A(H7N9) and A(H5N1) respectively, the median ages were 62y and 26y. In urban areas, 74% of cases of both viruses were male whereas in rural areas the proportions were 62% for A(H7N9) and 33% for A(H5N1). Among cases of A(H7N9) and A(H5N1), 75% and 71% reported recent exposure to poultry. The mean incubation periods of A(H7N9) and A(H5N1) were 3.1 and 3.3 days, respectively. On average, 21 and 18 contacts were traced for each A(H7N9) case in urban and rural areas respectively; compared to 90 and 63 for A(H5N1). The hospitalization fatality risk was 35% (95% CI: 25%, 44%) for A(H7N9) and 70% (95% CI: 56%, 83%) for A(H5N1). Interpretation The sex ratios in urban compared to rural cases are consistent with poultry exposure driving the risk of infection. However the difference in susceptibility to serious illness with the two different viruses remains unexplained, given that most A(H7N9) cases were in older adults while most A(H5N1) cases were in younger individuals. Funding Ministry of Science and Technology, China; Research Fund for the Control of Infectious Disease and University Grants Committee, Hong Kong Special Administrative Region, China; and the US National Institutes of Health.

Introductions and Evolution of Human-Origin Seasonal Influenza A Viruses in Multinational Swine Populations

“…These swine subtypes are similar to those presently found in humans (H1N1 and H3N2) but represent only a subset of those found in wild birds (16 HA subtypes and 9 NA subtypes), which are thought to be the natural reservoir for IAVs (4). Spillover events of IAVs occur frequently between host species, as exemplified by the isolation of avian H5N1 (5), avian H7N9 (6), and swine H3N2 "variant" (H3N2v) (7) viruses from humans in recent years. To date, however, none of these viruses have sustained onward transmission in humans, and the various barriers to successful adaptation to a new mammalian host species represent one of the most important outstanding questions in influenza virus biology (8,9).…”

A Study on the Prevalence and Virulence of Avian Influenza A (H5N1, H5N6 and H7N9) Viruses on Poultry at Lang Son Markets in Vietnam

“…In 2014 and 2015, 28 out of 180 cloacal and tracheal swab samples of the chicken sold at the periodic markets in Lang Son province were found positive with avian influenza A viruses (accounting for 15.55%); of which 9 were found positive with subtype H5 (accounting for 5%); and 5 were found positive with subtype N1 (accounting for 2.77%). This result was similar to that of [3], [9], [13].…”

“…The intravenous pathogenicity index (IVPI) of the virus strains was measured at the levels ranging from 2.9 (the viruses strain found on the chicken sold at local periodic markets) to 2.92 (the viruses strain H5N1 and H5N6 isolated on illegally imported chicken from China and ducks sold at border markets in Lang Son). The results were similar to the analysis of [3], [7], [8], [9], [12], and [15] in their studies on sickness causing characteristics of avian influenza viruses on poultry.…”

“…Thus, since March 2013 H7N9 viruses infection on human continuously occurred in China. This finding was similar to that of [3], [5], [14], [15]. The results show that there was no prevalence of avian influenza viruses subtype H7N9 on commercial poultry sold at border and local markets in Lang Son.…”

Two novel reassortants of avian influenza A (H5N6) virus in China

“…However, on 6 May 2014, a fatal H5N6 human infection was reported in Sichuan Province, China (China CDC, 2014;WHO, 2014b). The patient was a poultry dealer working directly in live poultry markets (LPMs), recently shown to play a key role in human infection with influenza A (H7N9 and H10N8) viruses (Cowling et al, 2013;Gao, 2014;Zhang et al, 2014). However, the origin of the novel H5N6 virus remains unknown.…”