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Detection of mild to moderate influenza A/H7N9 infection by China’s national sentinel surveillance system for influenza-like illness: case series

BMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f3693 (Published 24 June 2013) Cite this as: BMJ 2013;346:f3693

Rapid Response:

Re: Detection of mild to moderate influenza A/H7N9 infection by China’s national sentinel surveillance system for influenza-like illness: case series

The alarm of a novel avian influenza A (H7N9) virus has been ringing since March 22, 2013, when three cases of pneumonia with unknown causes were reported to China CDC from Shanghai CDC [1]. According to the meeting on May 21, 2013, jointly held by National Health and Family Planning Commission of P.R.China and World Health Organization at the 66th World Health Assembly at Geneva, there has been an accumulative total of 130 laboratory-confirmed cases of H7N9 infection in 10 provinces in China, including 36 deaths (Table 1).

Though the source of infection has not been fully identified, human infection with H7N9 virus has been associated with live-poultry markets [2,3]. As of May 15, Chinese Ministry of Agriculture found 52 positives samples from live poultry and environment, but the virus is not pathogenic; Chinese Ministry of Forestry has not found positive samples of wild migratory birds. Up to today, 90 (69.2%) of the total patients had a history of exposure to birds or live-poultry markets (Table 1). In April, the local government closed live-poultry markets in Shanghai (Apr 6), Nanjing (Apr 8) and Hangzhou (Apr 15). After a maximum incubation period of 7 days, there was no new outbreak in Shanghai and Hangzhou, except for one new case in Nanjing. The rapid decline of case numbers strengthens the possibility of live-poultry markets as infection source, though the possibility of seasonality could not be excluded.

The accumulating epidemiologic evidence suggests there is no evidence of sustained human-to-human transmission. A total of 2554 close contacts of the130 cases were checked. All were normal except for 4 family clusters. However, the family clusters can not exclude the possibility of co-exposure (father-son cases in Shanghai and Shandong, father-daughter cases in Jiangsu, one spouse case in Shanghai). However, human-to-human transmission is possible under appropriate conditions [4].

The outbreak of this avian influenza A H7N9A is characterized by male (70.8%) and age (over 60 years, 54.6%) at higher risk. The overall fatality rate was 27.7%, with higher rates for male (30.4% vs. 21.1%, P for chi square=0.28) and age (39.4% vs. 13.6% over 60 year of age vs. less than 60 years of age, P for chi square=0.001) (Table 1).

“Until the traditional sources are completely under control, new cases and new locations may still pop out”, stated by delegations of Ministry of National Health and Family Planning Commission of P.R.China at the 66th World Health Assembly.

References:
1. Gao R, Cao B, Hu Y, et al. Human infection with a novel avian-origin influenza A (H7N9) virus. N Engl J Med 2013;368(20):1888-97.
2. Chen Y, Liang W, Yang S, et al. Human infections with the emerging avian influenza A H7N9 virus from wet market poultry: clinical analysis and characterisation of viral genome. Lancet 2013 April 25 (Epub ahead of print).
3. Bai T, Zhou J, Shu Y. Serologic Study for Influenza A (H7N9) among High-Risk Groups in China. N Engl J Med. 2013 May 29 (Epub ahead of print).
4. Zhu H, Wang D, Kelvin DJ, et al. Infectivity, Transmission, and Pathology of Human H7N9 Influenza in Ferrets and Pigs. Science. 2013 May 23. [Epub ahead of print]

Competing interests: Z.J.Z. served as delegates of National Health and Family Planning Commission of P.R.China at the 66th World Health Assembly.

05 July 2013
Zhi-Jiang Zhang
Associate Professor
Wuhan University
185 Donghu Road