Epidemiological characterization of a cluster of COVID-19 caused by SARS-CoV-2 Omicron variant at a construction site in Qingpu District， Shanghai / 上海预防医学

ABSTRACT

ObjectiveTo determine the epidemiological characteristics of a cluster of SARS-CoV-2 Omicron variant at a construction site and provide evidence for further COVID-19 prevention and control. MethodsDemographic data of all COVID-19 cases at a construction site in Qingpu District， Shanghai， and basic information of the construction site were retrospectively collected through filed investigation. Descriptive epidemiology was used for the analysis. Basic reproduction number （R0） and time-dependent reproduction number （Rt） were calculated using R program. ResultsDuring April 12 and May 8， 2022， a total of 314 cases were reported at the construction site， with an attack rate of 60.62%. The attack rate significantly differed between workers and managers （χ2=10.868， P<0.001）， whereas did not differ statistically by gender （χ2=0.358， P=0.550） or by vaccination status （χ2=2.861， P=0.091）. The age of all cases ranged from 5 months of age to 68 years， with a media age of 49.0 years （interquartile range： 39.8， 54.0）. In all cases， male was predominant （83.44%）. Moreover， the epidemic was mainly concentrated in the workers’ dormitory area， with infected cases identified in all buildings of each dormitory area. The attack rate ranged between 33.33% and 87.50% across the buildings. Symptoms and signs were observed among 43.0% of all cases， of which major clinical manifestations included cough （33.33%）， fever （30.37%） and headache （17.04%）. Clinical manifestations did not differ by gender （χ2=1.275， P=0.259） or by vaccination status （χ2=0.186， P=0.666）. Additionally， R0 was estimated to be 6.08 （95% confidence interval： 4.49‒8.02）. The Rt showed a decline in the beginning， followed by an increase and a re-decline. ConclusionThe cluster epidemic of COVID-19 caused by Omicron variant at the construction site is highly contagious， spreads rapidly and quietly， causes mild symptoms， which finally resulted in a large number of infected cases. It warrants rapid and strict containment when an epidemic occurs at construction sites.