Low secondary transmission rates of SARS-CoV-2 infection among contacts of construction laborers at open air environment.

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection spreads through droplet and aerosols. Household contacts have a high risk of infection and transmission outside the home can occur at closed and open locations. We studied the transmission risk at open environment among contacts of construction laborers. Close contacts of 18 SARS-CoV-2 infected construction laborers were assessed for symptomatic or asymptomatic infection. Contacts were classified as: a) persons at residence of index case b) persons at workplace (open and closed environment), and c) persons outside the index case residence or workplace who are traceable. Relative risk of infection among contacts at different locations and observed parameters were compared between them. Four hundred and ninety-six contacts were assessed. The secondary transmission rate was maximum among household contacts (n=28, 43.7%) followed by contacts at closed environment at workplace (n=44, 26%), traceable other contacts (n=8, 15.7%) and contacts at open environment at workplace (n=3, 1.4%). Relative risk of SARS-CoV-2 infection among household contacts was 30.9 (CI 9.7-98.3, p<0.001) compared to open environmental work contacts and 1.68 (CI 1.15-2.44, p=0.006) compared to closed environmental work contacts. Relative risk was 18.3 (CI 5.8-58.2, P<0.001) among closed environmental work contacts compared to open environmental work contacts. One index and one secondary case died. The low secondary transmission rate of SARS-CoV-2 infection among open environmental contacts emphasizes the fact that free air flow has the ability to dilute or probably blow away the virus particles and lowers the transmission risk substantially.