SARS-CoV-2 seroprevalence in healthcare workers of a Swiss tertiary care centre at the end of the first wave: a cross-sectional study

• Main Authors: Gilbert Greub, Giuseppe Pantaleo, Oriol Manuel, Urania Dafni, Valérie D'Acremont, Estelle Moulin, Bruno Grandbastien, Thierry Calandra, Sylvain Meylan, Frederic Lamoth, Zoi Tsourti, Michael A Lobritz, Jean Regina, Philippe Bressin, Laurence Senn, Cyril Andre, Craig Fenwick, Antony Croxatto, Isabelle Guilleret, Catherine Lazor-Blanchet, Oliver Peters, Michael Currat, Laurence Posset, Fady Fares, Vassili Soumas, Séverine Bignon, Elisa Corne, Joana Da Silva Quelhas, Allan Dussex, Dominique Ker, Patricia Mosset, Eugénie Prouvost, Kyllian Ruscio, Sandrine Piccon, Fleur Valterio, Emilie Allain, Charles Guay, Zahra Hezari, Yoann Levet, Marie-Agnès Prevost, Adeline Rognon, Homa Salehi-Gysel, Cécile Starck, Aurélie Tornier, Sara Torres da Fonseca, Aline Udriot
• Format: Article
• Language: English
• Published: BMJ Publishing Group 2021-07-01
• Series: BMJ Open
• Online Access: https://bmjopen.bmj.com/content/11/7/e049232.full

Objective To assess the SARS-CoV-2 transmission in healthcare workers (HCWs) using seroprevalence as a surrogate marker of infection in our tertiary care centre according to exposure.Design Seroprevalence cross-sectional study.Setting Single centre at the end of the first COVID-19 wave in Lausanne, Switzerland.Participants 1874 of 4074 responders randomly selected (46% response rate), stratified by work category among the 13 474 (13.9%) HCWs.Main outcome measures Evaluation of SARS-CoV-2 serostatus paired with a questionnaire of SARS-CoV-2 acquisition risk factors internal and external to the workplace.Results The overall SARS-CoV-2 seroprevalence rate among HCWs was 10.0% (95% CI 8.7% to 11.5%). HCWs with daily patient contact did not experience increased rates of seropositivity relative to those without (10.3% vs 9.6%, respectively, p=0.64). HCWs with direct contact with patients with COVID-19 or working in COVID-19 units did not experience increased seropositivity rates relative to their counterparts (10.4% vs 9.8%, p=0.69 and 10.6% vs 9.9%, p=0.69, respectively). However, specific locations of contact with patients irrespective of COVID-19 status—in patient rooms or reception areas—did correlate with increased rates of seropositivity (11.9% vs 7.5%, p=0.019 and 14.3% vs 9.2%, p=0.025, respectively). In contrast, HCWs with a suspected or proven SARS-CoV-2-infected household contact had significantly higher seropositivity rates than those without such contacts (19.0% vs 8.7%, p<0.001 and 42.1% vs 9.4%, p<0.001, respectively). Finally, consistent use of a mask on public transportation correlated with decreased seroprevalence (5.3% for mask users vs 11.2% for intermittent or no mask use, p=0.030).Conclusions The overall seroprevalence was 10% without significant differences in seroprevalence between HCWs exposed to patients with COVID-19 and HCWs not exposed. This suggests that, once fully in place, protective measures limited SARS-CoV-2 occupational acquisition within the hospital environment. SARS-CoV-2 seroconversion among HCWs was associated primarily with community risk factors, particularly household transmission.