A contact tracing prospective cohort retrieving epidemiological facts on SARS-CoV-2 transmission aspects; a serological analysis

Abstract

Introduction Novel coronavirus spread seems mysterious enough for convincing us to double check the indices being used to predict its transmission. Serological analysis was applied for assessing some metric epidemiological aspects of the infection and its transmissibility among people who were in contact with SARA-CoV-2 patients. Methods In this contact tracing prospective cohort study, 453 contact cases of forty COVID 19 patients were followed for three months. SARS-CoV-2 patients were diagnosed by real time polymerase chain reaction testing of nasopharyngeal samples. The history of infectiousness was detected by serological testing of IgG and IgM. Trained expert team completed two questionnaires and blood samples were taken by experts in laboratory. Data were analyzed using SPSS (Ver.21) and R software. Some important epidemiological characteristics of the infection were calculated. Results Mean age of SARS-CoV-2 patients and contact cases were 53.0±18.2 and 30.8±19.3 years, respectively. Overall R0 of the infection was 2.56. Household and non-household secondary attack rates (SAR) were 20% (95%CI; 12.7 – 27.3) and 11.3% (95%CI; 6.1-16.5), respectively. Transmission probability in each contact was 0.0205 and the serial interval was 6.4±4.6 (95% CI; 5.2–7.6) days. SAR among contact cases who exposed asymptomatic primary cases (28%, 95%CI; 10-46%) was higher than that (13.8%, 95%CI;9.4-18.2) among contact cases exposing to symptomatic patients. Conclusions We concluded a herd immunity between 60 and 65% is needed in human communities. Findings demonstrated how much reduction in infection R0 is predicted based on both clinical and public health interventions.