Epidemiological Characteristics And Risk Factors Of Human Infection With Avian Influenza A (H7N9) Virus In Mainland China

ObjectiveThis study was aimed at investigating the epidemiological characteristics of human infection with avian influenza A(H7N9) cases in China to improve the understanding of the disease, and exploring the risk factors of recent H7N9 cases adopting case-control study and to provide the scientific evidence for the future adjustment of preventive strategy and control measures.Methods1. Epidemiological characteristics of human infection with avian influenza A (H7N9) virus in mainland ChinaIncluding confirmed cases of human infection with H7N9 avian virus in China since 2013 as object of this study, collecting relevant information from various monitoring systems and on-sight researches, adopting epidemiological methods to analysis the characteristics of time, area and population distribution of the disease.Establishing database via Excel 2013, thus summarize, clarify, tabulate and plot based on the information of case report cards and research reports; statistical analysis via statistical software SAS9.3. Adopting statistical methods such as descriptive statistical analysis and χ2 test, etc.2. Risk Factors of Human Infection with Avian Influenza A (H7N9) Virus in mainland ChinaAdopting 1:4 matched case-control study, using age, sex and place of residence as matching requirements,81 confirmed H7N9 cases and 340 randomly selected control were included in this study. Using specially designed research questionnaire, and conduct face-to-face survey to cases and controls. The main content of the investigation includes basic health conditions, possible exposure to poultry, routine behavior and habits, etc.Establish database via EPIDATA 3.0, using SAS 9.3 to conduct single and multivariable conditional Logistic regression analysis, and adopting Fisher exact probability method and unconditional Logistic regression analysis method when necessary.Results1. Epidemiological Characteristics of Human Infection with Avian Influenza A (H7N9) Virus in mainland China1.1 Epidemic features:The human infection H7N9 avian virus appears to have significant seasonal feature. December to Marchwas the peak period of epidemic, while July to September is the low season of morbidity. Human infection of H7N9 Bird Flu comparatively concentrate on provinces in east and southeast China; however, due to the increase of towns and provinces with newly reported cases, the epidemic area continue to expand. The basic demographic characteristics of human infection of H7N9 Bird Flu does not show significant alteration, male and senior individuals remain to be the major cases of infection; although case percentage of junior individual infections has a growing trend. The percentages of retired population decreased in the recent epidemic wave while no significant changes was observed in the occupation of workers, farmers and households and unemployed.1.2 The mortality risk of the disease has currently increased, and the mortality rate at present is 40.85%. No significant difference of the mortality rate were found between different sex.1.3 In recent cases, the time interval between morbidity, first inspection, hospital admission and case confirmation has been shortened, although in cases using Oseltamivir as treatment the time interval remains 6 days.1.4 Confirmed H7N9 cases remain sporadically, and research does not show the virus obtaining continuous human-to-human transmission ability yet.1.5 About 80% of the confirmed cases have history of exposure to poultry previous to morbidity, which indicates that live poultry market and the poultry from such markets remains a major factor of infection and morbidity of the disease.2. Risk Factors of Human Infection with Avian Influenza A (H7N9) Virus in mainland China2.1 Among basic conditions of confirmed cases and control cases, sex, age and place of residence being in city or in rural area does not have statistical differences, however, in confirmed cases the survey in rather high percentage is answered by a delegate (31%,χ2=22.78,P≤0.001).2.2 Multiple factor analysis results showed that risk factors of infection includes underlying chronically diseases (OR=3.30), visiting live poultry market (OR=8.21), ever stayed at the live poultry stalls (OR=8.32), raising domestic live poultry (OR= 19.43), while the protective factors include frequently hand cleaning (OR=0.12), applying hand soup while washing hand (OR=0.25).DiscussionCompared to previous studies, the epidemiological characteristics of human infection with H7N9 virus did not not show significant variation, however, the recent mortality rate has gone up. The detection and confirmation ability of H7N9 cases in China has comparatively improved as the time interval between morbidity, first inspection, hospital admission and case confirmation has been shortened, although the treatment time using Oseltamivir remains basically the same, which might have caused most cases missing the optimal cure time. The analysis of Oseltamivir treatment time between different provinces and between child and total cases indicate that early detection, early diagnosis and early treatment may reduce the incidence of severe and death. Epidemiological research results analysis indicates that the human-to-human transmission ability of H7N9 avian virus is rather limited, and that the disease cannot yet spread continuously among human.Live poultry market remains the major infection source of human infection with H7N9 avian influenza virus, and live poultry stalls played a significant role in the infection in the market. People with underlying diseases, especially pulmonary disease and diabetes may be the high-risk group of infection. And good hand hygiene habits may decrease the risk of infection. While we also find that been to the already-slaughtered-poultry stalls and contact with already-slaughtered-poultry has nothing to do with virus infection. The fundamental measures of controlling human infection with H7N9 avian influenza virus is to advance the upgrading and transformation of the domestic poultry industry, and to realize "poultry designated slaughter, concentrative quarantine, certified-poultry-only market".