Abstract：Objective An epidemiological investigation and analysis was conducted on a cluster epidemic of COVID-19 in Zhuhai City so as to provide a basis for prevention and control strategies. Methods Field epidemiological methods were applied to surveying 7 cases, 3 cases of asymptomatic infection and their close contacts. Their epidemiological characteristics and transmission chains were described and analyzed. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid was detected by real-time fluorescence reverse transcriptase polymerase chain-reaction. Results From January 16 to 21 in 2020, 18 members from 4 families of Yu family arrived in batches in Zhuhai from Wuhan and lived in GLHT hotel. They had a dinner party on the New Year's eve on January 24. The onset of the first case was on January 27, but the case was detected and confirmed on February 12. From February 12 to 28, 7 of 17 close contacts were tested positive for SARS-CoV-2 nucleic acid during the concentrated quarantine period. On the seventh day after the quarantine (March 5), another two persons were detected positive, and both of them were asymptomatic infected patients. A total of 7 cases and 3 asymptomatic infected patients were found in this epidemic. Analysis of transmission chains showed 4 generations of infection, and their exposure time was before the concentrated quarantine. Conclusions COVID-19 is infectious 3 days before the onset of symptoms. The longest time forpositive conversion of SARS-CoV-2 nucleic acid in close contacts after the exposure was ≥ 15 days, andthe 14-day quarantine period is not enough to exclude all infected persons.
2021, Vol. 28 
