Epidemic characteristics of influenza-like cases monitored in sentinel sites in Hunan Province, 2017-2020
ZENG Ge, HUANG Chao-yang, WANG Xiao-lei, LIU Zi-yan, LUO Kai-wei, HUANG Yi-wei, LI Wen-chao, ZHAO Shan-lu, DAI Zhi-hui, CHEN Sheng-bao, YANG Hao, SUN Qian-lai, HU Shi-xiong
Hunan Provincial Center for Disease Control and Prevention, Changsha, Hunan 410005, China
Abstract：Objective To understand the epidemiological characteristics of influenza-like illness (ILI) in Hunan Province by analyzing the sentinel surveillance results of ILI cases in Hunan Province from 2017 to 2020, and to provide a basis for influenza prevention and control in Hunan Province. Methods We collected the sentinel surveillance data and etiological detection data about ILI in Hunan Province from 2017 to 2020 through the Chinese Influenza Surveillance Information System. Statistical analyses were performed using Excel 2007 and SPSS 20 software. Results A total of 799,699 cases of ILI were reported by 23 sentinel hospitals in Hunan Province during 2017-2020, and the ILI% was 4.58%. The ILI% in 2017-2018, 2018-2019, and 2019-2020 were 5.23%, 4.12% and 4.42%, respectively (χ2=8,469.13, P<0.05). The age distribution of ILI reports in the monitoring years from 2017 to 2020 was similar, and the composition ratio was found to be the highest in 0-year-old age group, followed by 5-year-old age group, 25-year-old age group, 15-year-old age group and 60-year-old age group. The fluctuation range of ILI% in 2017-2020 was between 1.86% and 7.58%.There were two incidence peaks each year, one was in winter and spring (from December to February of the next year), and another one in summer (from May to July). The trend of ILI% in the three years was basically the same. There were differences in the overall ILI% report among cities and prefectures in Hunan Province(χ2=173,310.88, P<0.05), and the top five cities and prefectures were Yueyang City, Yongzhou City, Zhangjiajie City, Xiangtan City and Changde City. A total of 77,754 ILI specimens were collected from sentinel hospitals in Hunan Province during 2017-2020, and 12,243 were positive for influenza virus, with the positive rate of 15.75%. Among the positive specimens, influenza A (H3N2), A (H1N1), B Victoria (BV) and B Yamagata (BY) accounted for 35.87%, 29.69%, 19.05% and 15.18%, respectively. Conclusion The epidemic of ILI cases in Hunan Province in 2017-2020 showed two seasonal peaks occurringrespectively in winter-spring and summer. Overall, influenza type A virus was the main predominant strain in 2017-2020, and the main infected population was children under 5 years old.
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