- Dennis KM Ip, clinical assistant professor1,
- Qiaohong Liao, public health officer 2,
- Peng Wu, post doctorate fellow1,
- Zhancheng Gao, professor and respiratory physician3,
- Bin Cao, professor and infectious disease physician4,
- Luzhao Feng, public health officer2,
- Xiaoling Xu, respiratory physician5,
- Hui Jiang, public health officer2,
- Ming Li, public health officer2,
- Jing Bao, respiratory physician3,
- Jiandong Zheng, public health officer2,
- Qian Zhang, public health officer2,
- Zhaorui Chang, public health officer2,
- Yu Li, public health officer2,
- Jianxing Yu, public health officer2,
- Fengfeng Liu, public health officer2,
- Michael Y Ni, clinical assistant professor1,
- Joseph T Wu, associate professor1,
- Benjamin J Cowling, associate professor1,
- Weizhong Yang, medical epidemiologist and deputy director6,
- Gabriel M Leung, professor1,
- Hongjie Yu, medical epidemiologist and director2
- 1Infectious Disease Epidemiology Group, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China
- 2Division of Infectious Disease, Key Laboratory of Surveillance and Early-warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing 102206, China
- 3Department of Respiratory and Critical Care Medicine, Peking University People’s Hospital, Beijing, China
- 4Department of Infectious Diseases and Clinical Microbiology, Beijing Chao-Yang Hospital, Beijing Institute of Respiratory Medicine, Capital Medical University, Beijing, China
- 5Department of Respiratory Medicine, Anhui Province Hospital, Hefei, China
- 6Office of the Director, Chinese Center for Disease Control and Prevention, Beijing, China
- Correspondence to: G M Leung and H Yu
- Accepted 5 June 2013
Objective To characterise the complete case series of influenza A/H7N9 infections as of 27 May 2013, detected by China’s national sentinel surveillance system for influenza-like illness.
Design Case series.
Setting Outpatient clinics and emergency departments of 554 sentinel hospitals across 31 provinces in mainland China.
Cases Infected individuals were identified through cross-referencing people who had laboratory confirmed A/H7N9 infection with people detected by the sentinel surveillance system for influenza-like illness, where patients meeting the World Health Organization’s definition of influenza-like illness undergo weekly surveillance, and 10-15 nasopharyngeal swabs are collected each week from a subset of patients with influenza-like illness in each hospital for virological testing. We extracted relevant epidemiological data from public health investigations by the Centers for Disease Control and Prevention at the local, provincial, and national level; and clinical and laboratory data from chart review.
Main outcome measure Epidemiological, clinical, and laboratory profiles of the case series.
Results Of 130 people with laboratory confirmed A/H7N9 infection as of 27 May 2013, five (4%) were detected through the sentinel surveillance system for influenza-like illness. Mean age was 13 years (range 2-26), and none had any underlying medical conditions. Exposure history, geographical location, and timing of symptom onset of these five patients were otherwise similar to the general cohort of laboratory confirmed cases so far. Only two of the five patients needed hospitalisation, and all five had mild or moderate disease with an uneventful course of recovery.
Conclusion Our findings support the existence of a “clinical iceberg” phenomenon in influenza A/H7N9 infections, and reinforce the need for vigilance to the diverse presentation that can be associated with A/H7N9 infection. At the public health level, indirect evidence suggests a substantial proportion of mild disease in A/H7N9 infections.
We thank staff members of the Bureau of Disease Control and Prevention, Health Emergency Response Office of the National Health and Family Planning Commission, and provincial and local departments of health for assisting with administration and data collection; staff members at county, prefecture, and provincial government offices, and at the Centers of Disease Control and Prevention in Shanghai, Jiangsu, Zhejiang, Anhui, Henan, Beijing, Shandong, Jiangxi, Fujian, and Hunan provinces for assisting with the field investigation, administration, and data collection.
Contributors: GML and HY conceptualised the study design and supervised the study. QL, ZG, BC, LF, XX, HJ, ML, JB, JZ, QZ, ZC, YL, JY, FL, WY, and HY acquired the data. DKMI, QL, PW, MYN, GML, and HY analysed and interpreted the data. DKMI and PW drafted the manuscript. All authors critically revised and approved the final manuscript. DKMI, QL, PW, ZG, and BC contributed equally to this work. GML and HY are guarantors.
Funding: This study received funding from the US National Institutes of Health (Comprehensive International Program for Research on AIDS grant U19 AI51915); the China-US collaborative program on emerging and re-emerging infectious diseases. The study was also funded by grants from the Chinese Ministry of Science and Technology (2012 ZX10004-201); the Harvard Center for Communicable Disease Dynamics from the National Institute of General Medical Sciences (grant U54 GM088558); the Research Fund for the Control of Infectious Disease, Food, and Health Bureau (government of the Hong Kong Special Administrative Region), and the area of excellence scheme of the Hong Kong University grants committee (grant AoE/M-12/06). The funding bodies had no role in study design, data collection and analysis, preparation of the manuscript, or the decision to publish.
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare that: support from the US National Institutes of Health, China-US collaborative program on emerging and re-emerging infectious diseases, Chinese Ministry of Science and Technology, Harvard Center for Communicable Disease Dynamics from the National Institute of General Medical Sciences, government of the Hong Kong Special Administrative Region, and Hong Kong University for the submitted work; DKMI has received research funding from Hoffmann-La Roche; BJC has received research funding from MedImmune, and consults for Crucell NV; GML has received speaker honorariums from HSBC and Credit Lyonnais Securities Asia; no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: The National Health and Family Planning Commission of China determined that the collection of data from A/H7N9 cases was part of a continuing public health investigation of an emerging outbreak and was exempt from institutional review board assessment.
Data sharing: No additional data available.
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