COVID-19 Seroprevalence in Military Police Forces, Southern Brazil

Background: Limited data is available regarding the frequency of covid-19 in populations that are highly exposed to SARS-CoV-2. Methods: In this cross-section study we evaluated covid-19 seroprevalence in military police forces of ten major cities in Rio Grande do Sul, South of Brazil. Sampling was randomly performed in clusters, in respect to the number of professionals at service per city and military unit. Research subjects were evaluated on July 23, 2020. Clinical information was obtained, and venous blood was taken for ELISA testing (IgA, and IgG antibodies). Findings: Sample size consisted of 1,592 military workers (33.6% of study population). They were mostly man (81.2%) and young (median 34 years-old). Most had been asymptomatic (75.3%) during pandemia, and 27.5% reported close contact with covid-19 cases (after a median time of 21 days). Antibodies were detected in 3.3%, mostly IgA (2.7%), and IgG (1.7%). After 3 weeks, 66.7% of IgA and IgG results turned negative, in addition to 78.3% and 100% of borderline IgA and IgG results, respectively. Asymptomatic people were more prone to have negative antibody titters in the second run. Interpretation: The seroprevalence of COVID-19 amongst military police was at least 3.4 higher than the findings of other studies performed in the general population, in the same cities and dates. Most detectable antibodies were of IgA class which implies recent exposure in Southern Brazil. Funding Statement: This study was sponsored by Instituto Cultural Floresta. Declaration of Interests: The authors declare that they have no conflict of interest. Ethics Approval Statement: The study was approved by the independent ethics committee of all participant institutions. Participation in the study was voluntary and required signed consent of the research subject, whose identity was preserved at all times.