Secondary Attack Risk,clinical Characteristics And Validity Of Nucleic Acid Testing In Close Contacts Of COVID-19 Cases In Guangzhou

ObjectiveThis study was aimed to explore the risk of SARS-CoV-2 infection in close contacts of COVID-19 case in China under different exposure modes and compare the differences in clinical characteristics between index and second-generation cases,as well as to calculate the sensitivity and specificity values of RT-PCR testing,so as to provide a scientific basis for the prevention and control of SARS-CoV-2 infection in close contacts in China.MethodsData were obtained from the Guangzhou center for disease control and prevention,and 7948 close contacts of COVID-19 cases in Guangzhou from 13 January to 10 April 2020 were recruited for the study.The secondary attack of COVID-19 in close contacts under different exposure modes was described,and binary logistic regression analysis was used to analyze the factors of SARS-CoV-2 infection in close contacts.Further,χ2 test was used to analyze the differences in clinical characteristics and laboratory tests between the index case group and the second-generation cases group.Finally,the sensitivity and specificity of RT-PCR testing in close contacts at different prevention and control stages were calculated by descriptive analysis.Results(1)Secondary attack risk and risk factors for SARS-CoV-2:Among 7948 close contacts,4118(51.9%)were male,the median age of participants was 33.0 years((IQR,22.0 to 47.0 years).10 asymptomatic cases(0.1%)and 146 symptomatic cases(1.8%)were found,including 23 mild cases(15.8%),110 moderate cases(75.3%)and 13 severe or critical cases(8.9%).Household exposure had the highest incidence of COVID-19 at 9.8%.This was followed by entertainment place or workplace(1.3%)and healthcare setting(1.0%).Compared with household exposure,the ORs and 95%CIs in recreational or workplace(1.3%)and health care facilities were 0.16(0.09-0.28)and 0.08(0.04-0.18),respectively.The more severe of the index case is,the higher the risk of the close contact being infected(P trend<0.01).The secondary attack rates were 0.5%,2.3%,3.3%and 7.6%for exposure to asymptomatic,mild,moderate and severe or critical cases respectively.(2)Comparison of clinical characteristics between the index case group and the second-generation cases group:Of the 92 index cases,53(49.1%)were male,with a mean age of 48.1±17.3 years,and 64.1%of patients had comorbidities.In contrast,in 150 second-generation cases,59(43.4%)were male,with a mean age of 43.9±19.4 years,and 32.6%of patients had comorbidities.Clinical symptoms such as fever,dry cough,expectoration,fatigue and myalgia were more common in the index case group(P<0.05),and there were no deaths in either group.Neutrophil count was higher in the index case group than in the second-generation case group(P<0.05),and lymphocyte count was lower than in the second-generation cases group(P<0.05).(3)The sensitivity and specificity of RT-PCR testing:Among 7948 close contacts,the median number of nucleic acid tests was 2.0(IQR,1.0 to 3.0).All 156 cases were diagnosed after 6 nucleic acid tests in the study population.The sensitivity of the 1st nucleic acid tests was 72.44%,72.72%and 71.42%according to the different stages of prevention and control(domestic import,foreign import and foreign import association)respectively.ConclusionOur study shows that household contact is the main mode of transmission of SARS-CoV-2,and clinically more severe clinical cases are more likely to infect their close contacts.At the same time,second-generation cases were milder compared to their index cases.In terms of nucleic acid testing,the sensitivity of the 1st nucleic acid test for close contacts of COVID-19 was 72.44%.As the number of nucleic acid tests increases,the sensitivity increases,and multiple nucleic acid tests are recommended to reduce the missed diagnosis.