Monitoring Avian Influenza A(H7N9) Virus through National Influenza-like Illness Surveillance, China

Cuiling Xu, Fiona Havers, Lijie Wang, Tao Chen, Jinghong Shi, Dayan Wang, Jing Yang, Lei Yang, Marc-Alain Widdowson, and Yuelong Shu

Author affiliations: Chinese Center for Disease Control and Prevention, Beijing, China (C. Xu, L. Wang, T. Chen, J. Shi, D. Wang, J. Yang, L. Yang, Y. Shu); US Centers for Disease Control and Prevention, Atlanta, Georgia, USA. (F. Havers, M.-A. Widdowson)

Abstract

In China during March 4–April 28, 2013, avian influenza A(H7N9) virus testing was performed on 20,739 specimens from patients with influenza-like illness in 10 provinces with confirmed human cases: 6 (0.03%) were positive, and increased numbers of unsubtypeable influenza-positive specimens were not seen. Careful monitoring and rapid characterization of influenza A(H7N9) and other influenza viruses remain critical.

As of April 28, 2013, a total of 125 cases of avian influenza A(H7N9) virus infection and 24 related deaths were confirmed in humans in 8 provinces and 2 municipalities (hereafter called affected provinces/municipalities) of mainland China (1). The median age of patients was 63 years; most were male and had a history of exposure to live poultry (2). The first confirmed case was reported on March 31. On April 3, the Chinese Center for Disease Control and Prevention (China CDC) distributed primers and probes specific for avian influenza A(H7N9) virus to all national influenza surveillance network laboratories in China. To better understand the epidemiology, geographic spread, and clinical spectrum of this virus in China, we describe the Chinese National Influenza-Like Illness Surveillance Network (CNISN) and analyze data collected since March 4, 2013.

The Study

Figure 1

Thumbnail of Geographic distribution of national influenza surveillance sentinel hospitals in Beijing and Shanghai Municipalities and 8 provinces with confirmed human cases of avian influenza A(H7N9) virus infection, China, 2013.

Figure 1. . Geographic distribution of national influenza surveillance sentinel hospitals in Beijing and Shanghai Municipalities and 8 provinces with confirmed human cases of avian influenza A(H7N9) virus infection, China, 2013.

The CNISN includes 554 sentinel hospitals conducting surveillance for influenza-like illness (ILI; hereafter called sentinel hospitals) and 408 network laboratories in all 31 provinces of China (Figure 1). On a weekly basis, sentinel hospitals report the number of outpatient visits, by age group, for ILI and the total number of outpatients. Each week, 5–15 nasopharyngeal swab samples are collected from a convenience sample of patients who visit sentinel hospitals within 3 days of ILI onset. ILI is defined as temperature >38°C and cough or sore throat. Demographic and epidemiologic data, including age, sex, date of illness onset, and occupation, are also collected. Patient specimens are tested by real-time reverse transcription PCR or virus isolation in the affiliated laboratories.
On April 3, 2013, to enhance surveillance for influenza A(H7N9) virus, all network laboratories were required to increase the number of specimens to a minimum of 15/week and to test all specimens collected since March 4, 2013, for influenza A(H7N9) virus by real-time reverse transcription PCR as described (3,4). We analyzed data collected by CNISN during March 4–April 28. Population data by age group were provided by the National Bureau of Statistics of China.