SARS-CoV-2 infections and antibody responses among health care workers in a Spanish hospital after a month of follow-up

Moncunill, G.; Mayor, A.; Santano, R.; Jimenez, A.; Vidal, M.; Tortajada, M.; Sanz, S.; Mendez, S.; Llupia, A.; Aguilar, R.; Alonso, S.; Barrios, D.; Carolis, C.; Cistero, P.; Choliz, E.; Cruz, A.; Fochs, S.; Jairoce, C.; Hecht, J.; Lamoglia, M.; Martinez, M.; Moreno, J.; Mitchell, R.; Ortega, N.; Pey, N.; Puyol, L.; Ribes, M.; Rosell, N.; Sotomayor, P.; Torres, S.; Williams, S.; Barroso, S.; Vilella, A.; Trilla, A.; Varela, P.; Dobano, C.; Garcia-Basteiro, A. L.

Background. At the peak of the COVID-19 pandemic in Spain, cumulative prevalence of SARS-CoV-2 infection in a cohort of 578 randomly selected health care workers (HCW) from Hospital Clinic de Barcelona was 11.2%. Methods. A follow-up survey one month after the baseline (April-May 2020) measured SARS-CoV-2 infection by real time reverse-transcriptase polymerase chain reaction (rRT-PCR) and IgM, IgA, IgG and subclasses to the receptor-binding domain of the SARS-CoV-2 spike protein by Luminex. Prevalence of infection was defined by a positive SARS-CoV-2 rRT-PCR and/or antibody seropositivity. Results. The cumulative prevalence of infection at month 1 was 14.9% (84/565) and the seroprevalence 14.5% (82/565) for IgM and/or IgG and/or IgA. We found 25 (5%) new infections in participants without previous evidence of infection at baseline (501) and two participants seroreverted for IgM and/or IgG and/or IgA. Among seropositive participants at baseline, IgM and IgA levels generally declined at month 1 (antibody decay rates of 0.49 (95% CI, 0.40-0.60) and 0.34 (95% CI, 0.26-0.44)), respectively. Eight percent of the participants seroreverted for IgM and 11% for IgA. Subjects reporting COVID-19-like symptoms and laboratory and other technicians had higher risk of infection. The most frequent subclass responses were IgG1 and IgG2, followed by IgG3, with higher levels of IgG1, and only IgA1 but no IgA2 was detected. Conclusions. Our findings highlight the importance of a continuous and improved surveillance of SARS-CoV-2 infections in HCW, particularly in high risk groups. The decay of IgA and IgM levels have implications for seroprevalence studies using these isotypes.