Seroprevalence of antibodies against SARS-CoV-2 among health care workers in a large Spanish reference hospital
Authors: Garcia-Basteiro Alberto L , Moncunill Gemma , Tortajada Marta , Vidal Marta , Guinovart Caterina , Jiménez Alfons , Santano Rebeca , Sanz Sergi , Méndez Susana , Llupià Anna , Aguilar Ruth , Alonso Selena , Barrios Diana , Carolis Carlo , Cisteró Pau , Chóliz Eugenia , Cruz Angeline , Folchs Silvia , Jairoce Chenjerai , Hecht Jochen , Lamoglia Montserrat , Martínez Mikel J. , Mitchell Robert A. , Ortega Natalia , Pey Nuria , Puyol Laura , Ribes Marta , Rosell Neus , Sotomayor Patricia , Torres Sara , Williams Sarah , Barroso Sonia , Vilella Anna , Muñoz José , Trilla Antoni , Varela Pilar , Mayor Alfredo , Dobaño Carlota 
Published: May 2020

Background

Health care workers (HCW) are a high-risk population to acquire SARS-CoV-2 infection from patients or other fellow HCW. At the same time, they can be contagious to highly vulnerable individuals seeking health care. This study aims at estimating the seroprevalence of antibodies against SARS-CoV-2 and associated factors in HCW from a large referral hospital in Barcelona, Spain, one of the countries hardest hit by COVID-19 in the world.

Methods

From 28 March to 9 April 2020, we recruited a random sample of 578 HCW from the human resources database of Hospital Clínic in Barcelona. We collected a nasopharyngeal swab for direct SARS-CoV-2 detection through real time reverse-transcriptase polymerase chain reaction (rRT-PCR), as well as blood for plasma antibody quantification. IgM, IgG and IgA antibodies to the receptor-binding domain of the spike protein were measured by Luminex. The cumulative prevalence of infection (past or current) was defined by a positive SARS-CoV-2 rRT-PCR and/or antibody seropositivity.

Results

Of the 578 total participants, 39 (6.7%, 95% CI: 4.8-9.1) had been previously diagnosed with COVID-19 by rRT-PCR, 14 (2.4%, 95% CI: 1.4-4.3) had a positive rRT-PCR at recruitment, and 54 (9.3%, 95% CI: 7.2-12.0) were seropositive for IgM and/or IgG and/or IgA against SARS-CoV-2. Of the 54 seropositive HCW, 21 (38.9%) had not been previously diagnosed with COVID-19, although 10 of them (47.6%) reported past COVID-19-compatible symptoms. The cumulative prevalence of SARS-CoV-2 infection was 11.2% (65/578, 95% CI: 8.9-14.1). Among those with evidence of past or current infection, 40.0% (26/65) had not been previously diagnosed with COVID-19, of which 46.2% (12/26) had history of COVID-19-compatible symptoms. The odds of being seropositive was higher in participants who reported any COVID-19 symptom (OR: 8.84, 95% CI: 4.41-17.73). IgM levels positively correlated with age (rho=0.36, p-value=0.031) and were higher in participants with more than 10 days since onset of symptoms (p-value=0.022), and IgA levels were higher in symptomatic than asymptomatic subjects (p-value=0.041).

Conclusions

The seroprevalence of antibodies against SARS-CoV-2 among HCW was lower than expected. Thus, being a high-risk population, we anticipate these estimates to be an upper limit to the seroprevalence of the general population. Forty per cent of those with past or present infection had not been previously diagnosed with COVID-19, which calls for active periodic rRT-PCR testing among all HCW to minimize potential risk of hospital-acquired SARS-CoV-2 infections.