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The Lancet, Early Online Publication, 24 June 2013
doi:10.1016/S0140-6736(13)61171-XCite or Link Using DOI
This article can be found in the following collections: Public Health; Infectious Diseases (Respiratory tract infections); Respiratory Medicine (Respiratory tract infections)
Copyright © 2013 Elsevier Ltd All rights reserved.
Comparative epidemiology of human infections with avian influenza A H7N9 and H5N1 viruses in China: a population-based study of laboratory-confirmed cases
Benjamin J Cowling PhD a †, Lianmei Jin MD b †, Eric HY Lau PhD a, Qiaohong Liao MD c, Peng Wu PhD a, Hui Jiang MD c, Tim K Tsang MPhil a, Jiandong Zheng PhD c, Vicky J Fang MPhil a, Zhaorui Chang MD c, Michael Y Ni MPH a, Qian Zhang MD c, Dennis KM Ip MPhil a, Jianxing Yu MD c, Yu Li MD c, Liping Wang PhD c, Wenxiao Tu MD b, Ling Meng MD b, Joseph T Wu PhD a, Huiming Luo MD d, Qun Li MD b, Yuelong Shu PhD e, Zhongjie Li MD c, Zijian Feng MD b, Weizhong Yang MD f, Yu Wang PhD f, Prof Gabriel M Leung MD a Corresponding AuthorEmail Address, Dr Hongjie Yu MD c Corresponding AuthorEmail Address
Summary
Background
The novel influenza A H7N9 virus emerged recently in mainland China, whereas the influenza A H5N1 virus has infected people in China since 2003. Both infections are thought to be mainly zoonotic. We aimed to compare the epidemiological characteristics of the complete series of laboratory-confirmed cases of both viruses in mainland China so far.
Methods
An integrated database was constructed with information about demographic, epidemiological, and clinical variables of laboratory-confirmed cases of H7N9 (130 patients) and H5N1 (43 patients) that were reported to the Chinese Centre for Disease Control and Prevention until May 24, 2013. We described disease occurrence by age, sex, and geography, and estimated key epidemiological variables. We used survival analysis techniques to estimate the following distributions: infection to onset, onset to admission, onset to laboratory confirmation, admission to death, and admission to discharge.
Findings
The median age of the 130 individuals with confirmed infection with H7N9 was 62 years and of the 43 with H5N1 was 26 years. In urban areas, 74% of cases of both viruses were in men, whereas in rural areas the proportions of the viruses in men were 62% for H7N9 and 33% for H5N1. 75% of patients infected with H7N9 and 71% of those with H5N1 reported recent exposure to poultry. The mean incubation period of H7N9 was 3·1 days and of H5N1 was 3·3 days. On average, 21 contacts were traced for each case of H7N9 in urban areas and 18 in rural areas, compared with 90 and 63 for H5N1. The fatality risk on admission to hospital was 36% (95% CI 26—45) for H7N9 and 70% (56—83%) for H5N1.
Interpretation
The sex ratios in urban compared with rural cases are consistent with exposure to poultry driving the risk of infection—a higher risk in men was only recorded in urban areas but not in rural areas, and the increased risk for men was of a similar magnitude for H7N9 and H5N1. However, the difference in susceptibility to serious illness with the two different viruses remains unexplained, since most cases of H7N9 were in older adults whereas most cases of H5N1 were in younger people. A limitation of our study is that we compared laboratory-confirmed cases of H7N9 and H5N1 infection, and some infections might not have been ascertained.
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.
doi:10.1016/S0140-6736(13)61171-XCite or Link Using DOI
This article can be found in the following collections: Public Health; Infectious Diseases (Respiratory tract infections); Respiratory Medicine (Respiratory tract infections)
Copyright © 2013 Elsevier Ltd All rights reserved.
Comparative epidemiology of human infections with avian influenza A H7N9 and H5N1 viruses in China: a population-based study of laboratory-confirmed cases
Benjamin J Cowling PhD a †, Lianmei Jin MD b †, Eric HY Lau PhD a, Qiaohong Liao MD c, Peng Wu PhD a, Hui Jiang MD c, Tim K Tsang MPhil a, Jiandong Zheng PhD c, Vicky J Fang MPhil a, Zhaorui Chang MD c, Michael Y Ni MPH a, Qian Zhang MD c, Dennis KM Ip MPhil a, Jianxing Yu MD c, Yu Li MD c, Liping Wang PhD c, Wenxiao Tu MD b, Ling Meng MD b, Joseph T Wu PhD a, Huiming Luo MD d, Qun Li MD b, Yuelong Shu PhD e, Zhongjie Li MD c, Zijian Feng MD b, Weizhong Yang MD f, Yu Wang PhD f, Prof Gabriel M Leung MD a Corresponding AuthorEmail Address, Dr Hongjie Yu MD c Corresponding AuthorEmail Address
Summary
Background
The novel influenza A H7N9 virus emerged recently in mainland China, whereas the influenza A H5N1 virus has infected people in China since 2003. Both infections are thought to be mainly zoonotic. We aimed to compare the epidemiological characteristics of the complete series of laboratory-confirmed cases of both viruses in mainland China so far.
Methods
An integrated database was constructed with information about demographic, epidemiological, and clinical variables of laboratory-confirmed cases of H7N9 (130 patients) and H5N1 (43 patients) that were reported to the Chinese Centre for Disease Control and Prevention until May 24, 2013. We described disease occurrence by age, sex, and geography, and estimated key epidemiological variables. We used survival analysis techniques to estimate the following distributions: infection to onset, onset to admission, onset to laboratory confirmation, admission to death, and admission to discharge.
Findings
The median age of the 130 individuals with confirmed infection with H7N9 was 62 years and of the 43 with H5N1 was 26 years. In urban areas, 74% of cases of both viruses were in men, whereas in rural areas the proportions of the viruses in men were 62% for H7N9 and 33% for H5N1. 75% of patients infected with H7N9 and 71% of those with H5N1 reported recent exposure to poultry. The mean incubation period of H7N9 was 3·1 days and of H5N1 was 3·3 days. On average, 21 contacts were traced for each case of H7N9 in urban areas and 18 in rural areas, compared with 90 and 63 for H5N1. The fatality risk on admission to hospital was 36% (95% CI 26—45) for H7N9 and 70% (56—83%) for H5N1.
Interpretation
The sex ratios in urban compared with rural cases are consistent with exposure to poultry driving the risk of infection—a higher risk in men was only recorded in urban areas but not in rural areas, and the increased risk for men was of a similar magnitude for H7N9 and H5N1. However, the difference in susceptibility to serious illness with the two different viruses remains unexplained, since most cases of H7N9 were in older adults whereas most cases of H5N1 were in younger people. A limitation of our study is that we compared laboratory-confirmed cases of H7N9 and H5N1 infection, and some infections might not have been ascertained.
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.
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