Epidemiological survey and analysis on a cluster epidemic of coronavirus disease 2019
LIU Zhi-gang1, HU Chun-sheng2, ZHOU Yong-geng1, WANG Zhi-min1, ZHAO Shan-lu2, WU Jian-ge3, LONG Cai-hong3, DING Li2, FAN Xiang2, XIAO Li1
1. Qidong County Center for Disease Control and Prevention, Qidong, Hunan 426000, China; 2. Hunan Provincial Center for Disease Control and Prevention, Changsha, Hunan 410005, China; 3. Hengyang Municipal Center for Disease Control and Prevention, Hengyang, Hunan 421000, China
Abstract：Objective To analyze the characteristics of a cluster epidemic of coronavirus disease 2019 (COVID-19), to simultaneously explore the significance of serum specific antibody detection in the epidemiological survey of COVID-19, and to provide references for further improvement of COVID-19 prevention and control strategies. Methods A field epidemiological investigation was conducted on a cluster epidemic of COVID-19 in a county. All persons who came back from Hubei in this controlled area were classified as possible source of infection. Oropharyngeal swabs and serum samples were collected from close contacts of confirmed cases and suspicious sources of infection. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect nucleic acids from 2019 novel coronavirus (2019-nCoV) in oropharyngeal swab samples, and the enzyme linked immunosorbent assay (ELISA) was employed to detect serum specific immunoglobulin M (IgM) and immunoglobulin G(IgG) antibodies to 2019-nCoV. Results Five cases were tested positive for 2019-nCoV nucleic acids, one of which was continuously negative for the first 6 times, but positive in the seventh test. The 5 confirmed cases came from 2 different families, and there was no history of close contact between the first cases of the 2 families as well as between the first cases and the suspected source of infection. Among the close contacts, one, who had close contact with the first cases of the 2 families, was determined asasymptomatic infector whose serum IgM and IgG were positive but nucleic acid tests were negative for 7 times in the whole survey period. There were 77 cases with suspected infectious sources in the controlled area, and their nucleic acid tests were all negative, but serum IgG antibody was positive in 2 cases, which might be the infectious source of this cluster epidemic. Conclusions COVID-19 is prone to occurring intra-family transmission, and the existence of a relatively closed space is conducive to the possible transmission of 2019-nCoV. Specific antibody detection can be used as a supplement to nucleic acid test, which has great significance for detecting asymptomatic patients and tracing the infectious source of confirmed cases without a clear history of exposure.
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2020, Vol. 27 
