Asymptomatic, Mild, and Severe Influenza A(H7N9) Virus Infection in Humans, Guangzhou, China

Zongqiu Chen1, Hui Liu1, Jianyun Lu1, Lei Luo1, Kuibiao Li, Yufei Liu, Eric H.Y. Lau, Biao Di, Hui Wang, Zhicong Yang2, and Xincai Xiao2

Author affiliations: Guangzhou Center for Disease Control and Prevention, Guangzhou, China (Z. Chen, H. Liu, J. Lu, L. Luo, K. Li, Y. Liu, B. Di, H. Wang, Z. Yang, and X. Xiao); University of Hong Kong, Hong Kong, China (E.H.Y. Lau)

Abstract

Targeted surveillance for influenza A(H7N9) identified 21 cases of infection with this virus in Guangzhou, China, during April 1, 2013–March 7, 2014. The spectrum of illness ranged from severe pneumonia to asymptomatic infection. Epidemiologic findings for a family cluster of 1 severe and 1 mild case suggested limited person-to-person transmission of this virus.

During February–May 2013, the initial outbreak of human infection with avian influenza A(H7N9) virus in China resulted in 133 cases (1). Influenza A(H7N9) virus reemerged in southern China in October 2013 and had caused 85 laboratory-confirmed cases of infection in Guangdong Province as of March 7, 2014. In response to the outbreak, targeted surveillance programs were established in April 2013 in Guangzhou, the provincial capital of Guangdong Province. Here, we report results of this surveillance program through early 2014.

The Study

Since 2004, all clinical facilities in Guangzhou (population 13 million in 2013) have been required by the China National Health and Family Planning Commission to report any patient who meets the criteria of having pneumonia of unknown etiology (PUE): fever (>38°C), radiologic characteristics consistent with pneumonia, low-normal leukocyte count or low lymphocyte count in early-stage disease, and no alternative etiology (2). Upper or lower respiratory samples from these patients are collected for identification of possible causative pathogens. In response to the influenza A(H7N9) outbreak, PUE surveillance was enhanced in April 2013 by implementing laboratory testing specific for influenza A(H7N9) virus (3). Specimens are initially screened for influenza A and B viruses by real-time reverse transcription PCR (rRT-PCR); samples positive for influenza A are then subtyped as H1N1, H3N2, H5N1, or H7N9.

Surveillance for influenza-like illness (ILI) was initially conducted in 4 sentinel hospitals in Guangzhou and expanded to 19 hospitals in November 2013. Each hospital collects 10–20 convenience throat swab specimens weekly from ILI patients visiting the hospitals within 3 days of illness onset. The same laboratory screening protocols were adopted as for PUE surveillance.

Surveillance for influenza A(H7N9) virus was established in 24 live poultry markets (LPMs) in April 2013 and expanded to 42 LPMs in November 2013, covering all 12 districts in Guangzhou. From each LPM, 10–30 environmental samples are collected biweekly and tested by rRT-PCR. When human influenza A(H7N9) infection is confirmed, additional environmental sampling from epidemiologically linked LPMs is immediately launched to trace the possible source of infection. All poultry workers linked to influenza A(H7N9) virus–contaminated LPMs (i.e., LPMs with >1 virus-positive environmental samples identified) are placed under medical observation for 7 days. Throat swab specimens are collected within 24 hours for detection of influenza A(H7N9) infection and second swab specimens are collected if symptoms appear.

Close contacts of influenza A(H7N9) case-patients are defined as any family member who shares residence, social contacts who visit, and health care workers who provide medical services without effective personal protection (4) during the period from 1 day before illness onset to isolation (5). All close contacts are monitored for 7 days for any symptoms, and throat swab specimens are collected to detect possible person-to-person transmission.

Acknowledgments

We thank staff members of 12 district Center for Disease Control and Prevention offices in Guangzhou for their assistance in the field investigation and data collection.

This work was supported by grants from the National Science and Technology Major Projects of China (no. 2012ZX100004213-005) and Science and Technology Program of Guangzhou, China (no. 201102A213222).

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Technical Appendix

Technical Appendix. Geographic distribution of confirmed influenza A(H7N9) cases and live poultry markets sampled in Guangzhou, China. 120 KB

Suggested citation for this article: Chen Z, Liu H, Lu J, Luo L, Li K, Liu Y, et al. Asymptomatic, mild, and severe influenza A(H7N9) virus infection in humans, Guangzhou, China. Emerg Infect Dis [Internet]. 2014 Sep [date cited]. http://dx.doi.org/10.3201/eid2009.140424