This study is part of SeroCov-1, a hospital-based seroprevalence project of SARS-CoV-2 (Immunological dynamics within one-year period), coordinated by Alberto García-Basteiro, ISGlobal researcher, and medical doctor at the International Health Service of Hospital Clínic. This project aims at shedding light on the levels of exposure to SARS-CoV-2 at the Hospital Clínic of Barcelona, one of the reference centres in Spain for the diagnosis and treatment of COVID-19 disease. Data generated will have direct implications in human resources management and planning in the health system, as well as in the understanding of the different microbiological, clinical, immunological and nosocomial determinants of the disease and its transmission.

The real percentage of people infected by SARS-CoV-2 remains one of the great unknowns in this pandemic, since symptoms caused by the infection can range from imperceptible to very severe. According to García-Basteiro, knowing the prevalence of infection among healthcare workers is particularly important, since it helps estimate –and mitigate- their risk of exposure.

The research team measured antibodies against one of the SARS-CoV-2 proteins in blood samples from 578 staff members working at Hospital Clínic. In parallel, the Biomolecular Screening and Protein Technologies Unit and the Genomics Unit, led by Carlo Carolis and Jochen Hecht respectively, at the Centre for Genomic Regulation (CRG), performed PCR tests using nasopharyngeal swabs to detect active infections.

The results reveal that, of 578 study participants, 14 had an active infection (i.e. they were positive by PCR) at the time of recruitment, 39 had been previously diagnosed by PCR, and 54 had developed antibodies against the virus (signalling recent or past infection). Of these 54 individuals, 21 (39%) had not been diagnosed at the time of infection, and roughly half of these undiagnosed individuals did not develop any COVID-19 symptoms. The total number of participants with evidence of past or current infection (by PCR and/or serology) was 65, or 11.2%.Antibodies were generally detected after 10 days of symptom onset, and IgA antibodies could be detected slightly sooner than IgM or IgG antibodies.

Reference paper posted as a preprint on the medRxiV server:
García-Basteiro AL, Moncunill G, Tortajada M et al.
“Seroprevalence of antibodies against SARS-CoV-2 among health care workers in a large Spanish reference hospital.” 
medRxiv. 2020.04.27.20082289; https://doi.org/10.1101/2020.04.27.20082289

Related press release issued by ISGlobal (03/05/2020): First Serological Study among Health Care Workers in Spain Reveals Lower-than-expected Prevalence of SARS-CoV-2 Infection