Discussion

This is the first study to evaluate the prevalence of SARS-CoV-2 in HCPs in Brazil. Previous studies conducted elsewhere have addressed the question, mostly using real-time polymerase chain reaction (PCR) tests. The occupational health service of Massachusetts performed a study to assess COVID-19 prevalence in HCPs, revealing that 14.0% had a positive PCR test at the initial evaluation. ^{Reference Lan, Lan and Filler1} In Hong Kong, 29% of HCPs were found to be infected using PCR. ^{Reference Wong, Kwong and Wu2} In 2 Dutch hospitals, 6% of HCPs were infected with SARS-CoV-2 in March 2020. ³ However, conducting epidemiological surveys with PCR is not practical because PCR results reflect viral detection at the moment of sampling only. Alternatively, SARS-CoV-2 prevalence can be determined by antibody detection. In Italy, a study showed that 14.4% of HCPs working in the hospital had detectable IgM antibodies against SARS-CoV-2. ^{Reference Sotgiu, Barassi and Miozzo4} In the New York city area, a study conducted in June 2020 showed a 13.7% prevalence of SARS-CoV-2 antibodies in HCPs. ^{Reference Moscola, Sembajwe and Jarrett5} In a hospital in Regensburg, Germany, exposed HCPs did not develop any relevant IgG antibody levels over time. ^{Reference Malfertheiner, Brandstetter and Roth6}

In our study, a large proportion of HCPs had been exposed to SARS-CoV-2 (82.3%), had developed COVID-19 (34.6%), and had antibodies (5.6%) against SARS-CoV-2. Even though the manufacturer reported that the STANDARD Q COVID-19 IgM/IgG Duo Test had 94.3% sensitivity and 95.1% specificity (IgM and IgG combined), in our study, the test was able to detect only 34.6% (n = 27) of HCPs previously diagnosed with COVID-19. Therefore, our prevalence rates might have been underestimated.

For most of our patients, antibodies disappeared over time. Studies show that the average time for the reduction of antibody concentrations is very variable. Corroborating our findings, one Chinese study reported that antibodies decreased within 2–3 months after COVID-19 in a high proportion (71.1%) of individuals who recovered from infection. ^{Reference Long, Tang and Shi7} In another analysis, also from China, the decay of antibodies started between 4 and 5 weeks after the onset of symptoms. ^{Reference Liu, Wang and Zhao8} Asymptomatic individuals are more prone for early reversal of antibody titers to negative. ^{Reference Long, Tang and Shi7–Reference Paiva, Grisson and Chan9}

In conclusion, our results reveal that HCPs working in emergencies in Southern Brazil had a high rate (82.3%) of exposure to SARS-CoV-2, during the peak of the first wave of the COVID-19 pandemic in 2020. In total, 5.6% of HCPs manifested antibodies against SARS-CoV-2, which is probably an underestimation due to the limited sensitivity of the diagnostic test used in the study. Antibodies became negative over time in ∼50% of patients 3 weeks after their initial evaluation.