Euro Surveill. 2013 Jun 27;18(26):20510.

Case-control study of risk factors for human infection with influenza A(H7N9) virus in Jiangsu Province, China, 2013.

J Ai1, Y Huang2,3, K Xu1, D Ren3,4, X Qi1, H Ji1, A Ge1, Q Dai1, J Li1, C Bao1, F Tang1, G Shi3, T Shen3, Y Zhu (jszyf@jscdc.cn)1, M Zhou1,H Wang1

1. Jiangsu Provincial Center for Disease Control and Prevention, Nanjing, Jiangsu, China

2. Tongling Center for Disease Control and Prevention, Tongling, Anhui, China

3. Chinese Field Epidemiology Training Program, Chinese Center for Disease Control and Prevention, Beijing, China

4. Tongren Center for Disease Control and Prevention, Tongren, Guizhou, China

 

Abstract

To evaluate risk factors for human infection with novel avian influenza A (H7N9) virus, a case-control study was performed in Jiangsu, China. 25 cases and 93 controls matched by age, sex, and location were enrolled. Direct contact with poultry or birds in the two weeks before illness onset, chronic medical conditions (hypertension excluded),and environment-related exposures were significantly associated with H7N9 disease.

PMID: 23827526

 

Supplement:

Over the past decade, avian influenza derived from animal reservoirs has become a major challenge. Prior to 2011, H7N9 viruses were reported to only cause infections in fowl in many countries such as the Czech Republic, Spain, the US, and Mexico, but this was the first time that infected humans. Since it was discovered in February 2013, the emerging outbreak of human infections with a novel avian influenza A(H7N9) virus in China, has raised serious concerns for public health throughout the world. According to reports by China National Health and Family Planning Commission, a total of 130 confirmed cases of human infection including 37 deaths (28%) were reported in mainland China as of 27 May 2013.

Jiangsu province located in eastern China (one of the areas where the novel reassortant influenza A(H7N9) virus emerged earliest), it’s adjacent to Shanghai, Zhejiang, Anhui and Shandong province. There were 24 confirmed patients in Jiangsu province until April 22th. About 23.08% of the total number of cases in the country. The recent evolutionary analysis to the origins showed the virus was most possible infected H7N9 from poultry, but few descriptive studies have been reported on risk factors associated with avian influenza A (H7N9) virus infection, and how to effective prevent influenza H7N9 and reduce the risk for infection is seldom understood. To acquire these key information, We conducted a matched case-control study to identify potential risk factors for human influenza A(H7N9) cases.

We have three purposes of the research. The first, explore infection risk factors of infecting avian influenza A(H7N9) virus. The second, Clear whether live poultry exposure is one of the risk factors of infecting avian influenza A(H7N9) virus. The third, provided the scientific basis for prevention and control measures.

We carried out the surveys in eight cities which have the cases in the whole province, using case-control study method. We matched four neighbours as controls for each patient. The selection criteria included: testing negative for influenza A(H7N9) virus, same sex, no more than five-year age difference, and no respiratory tract symptom like cough or sore throat, or other symptoms like fever (≥38oC) within two weeks of illness onset of the matched case. Cases were defined according to the diagnosis and treatment programs of human infections with H7N9 virus issued by the National Health and Family Planning Commission of the People’s Republic of China.

We performed an epidemiological survey for all participants including demographic characteristics, health status, daily habits, and other potential risk behaviour, the activities and environment-related exposures within two weeks before the illness onset of the case.

In the multivariate conditional logistic regression model, three variables represented significant risk factors for human influenza A(H7N9) virus infection: direct contact with poultry or birds, chronic medical conditions (hypertension excluded) and environment-related exposures.

This study suggested People, especially those with underlying diseases, such as chronic bronchitis, diabetes, cancers, rheumatic arthritis, and immunodeficiency disease, could avoid the risk by reducing exposure to possibly contaminated environment. Persons exposed to poultry are advised to undertake appropriate protection and to develop correct hand washing habits. The most drastic measure would be closing the live poultry markets but if this is not possible, other measures such as segregating bird species, improving biosecurity, and having centralised poultry slaughtering locations, regular disinfection, and a periodical rest day, should be considered.

The advantages of this study were using the method of analysis of epidemiological explore the risk factors of avian influenza A(H7N9) virus infection for the first time and the study was carried out in time. The Case-control study was carried out by fixed professionals to complete all the way, the standard was unified.

Figure 1.The field epidemiological surveyFigure 1.The field epidemiological survey

Figure 2.Blood samples of control population were collectedFigure 2.Blood samples of control population were collected

Figure 3.Our investigador visited the wet marketFigure 3.Our investigador visited the wet market

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