Background Antibody (Ab) tests for SARS-CoV-2 virus allows for the estimation of incidence, level of exposure and duration of immunity acquired by a previous infection. In health workers, the hospital setting might convey a greater risk of infection. Aims To describe the frequency of immunoglobulin G (IgG) Abs (IgG-Abs) to the SARS-CoV-2 virus among workers at a third-level university hospital in Colombia. Methods In this cross-sectional study, we included medical and non-medical personnel with at least one real-time polymerase chain reaction (RT-PCR)/antigen test between March 2020 and March 2021. In April 2021, an IgG-Ab test against SARS-CoV-2 was conducted for all participants and replicated 2 weeks later in a random sample (10%). The frequency of IgG-Abs is presented based on status (positive/negative) and time elapsed since RT-PCR/antigen test (6 months). Results We included 1021 workers (80% women, median age 34 years (interquartile range 28-42), 73% medical personnel, 23% with previous positive RT-PCR/antigen). The overall seroprevalence was 35% (95% CI 31.6-37.4, 35% in medical and 33% in non-medical personnel). For those with a previous positive RT-PCR/antigen test, the seroprevalence was 90% (6 months). In participants with a previous negative RT-PCR/antigen test, the seroprevalence was 17% (6 months). Conclusions High IgG-Ab positivity was found in hospital personnel, regardless of work activities. The prevalence of detectable Abs differed by previous RT-PCR/antigen status and time elapsed since the diagnostic test. By following the immunologic response, antibody testing allows confirmation of SARS-CoV-2 infection in previously unidentified cases. We measured the frequency of long-term antibodies (IgG) among health workers in a Colombian hospital with differing levels of risk (medical and non-medical) and time elapsed since conventional testing. While antibodies decreased in previously confirmed cases, they progressively increased among those unaware of the infection. Our findings suggest that testing antibodies improved case identification and organizational decision-making.
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