Discussion

Psychiatric staff seroprevalence was surprisingly not increased compared with the general population in the Flanders region (adjusted seroprevalence, 3.0% v. 4.9%; χ² = 2.79; P = 0.095; Fig. 1), and even decreased compared with the Belgian population seroprevalence (3.0% v. 5.5%, χ² = 4.73; P = 0.030).^{Reference Herzog, De Bie, Abrams, Wouters, Ekinci and Patteet2} This finding was unexpected, as the psychiatric hospital continued its activities and was unable to implement routine use of PPE throughout most of the pandemic. Previous studies have indicated a higher seroprevalence among Belgian general hospital staff. Steensels et al reported a 6.4% seroprevalence among 3056 staff of a third-line general hospital sampled 22–30 April 2020.^{Reference Steensels, Oris, Coninx, Nuyens, Delforge and Vermeersch3} Another study among 834 healthcare providers from 17 Belgian hospitals screened 19–24 May 2020 reported a 8.8% seroprevalence.⁴ The relatively low seroprevalence in our study might be explained by early implementation of source control and transmission prevention (Fig. 1) and/or as a consequence of waning antibodies (measurement in June), after a longer interval since exposure in March or April.^{Reference Long, Tang, Shi, Li, Deng and Yuan5} However, all previously symptomatic staff members with antibodies reported having had COVID-19-related symptoms in March 2020, in the beginning of the epidemic. As we did not assess symptom severity, it is unclear to which extent early or mild cases, who may not generate anti-SARS-Cov-2 antibodies, were missed in this serosurvey. The same applies to, on average, 14 staff members who were on sick leave during our sampling window. Other limitations of this study include the single-centre design and testing of only 47.4% of staff, although all of the different staff functions were well represented in the sample.

This study represents the first hospital-wide screening for SARS-CoV-2 antibodies among psychiatric staff. Hospital-wide antibody screening can help evaluate transmission dynamics and infection control policies. Importantly, neither being involved in clinical care nor having been exposed to patients or co-workers with COVID-19 increased the odds of being seropositive, whereas having a suspected COVID-19-positive household contact did. These findings are in line with those previously reported among staff of a general hospital in Belgium,^{Reference Steensels, Oris, Coninx, Nuyens, Delforge and Vermeersch3} and indicate that, similar to what has been described in elderly care homes, staff being exposed to COVID-19 outside of the workplace could represent a source of infection in psychiatric facilities. Our data corroborate the findings from other authors that although patients with mental disorders are at increased risk of COVID-19 infection,^{Reference Wang, Xu and Volkow6,Reference Taquet, Luciano, Geddes and Harrison7} with appropriate precautions, in-patient psychiatric services do not represent COVID-19 outbreak hotspots, and even patients with COVID-19 who need in-patient psychiatric treatment can be managed safely.^{Reference Zhang, LeQuesne, Fichtel, Ginsberg and Frankle8,Reference Knowles, Aref-Adib, Moslehi, Aubrey-Jones, Obeney-Williams and Leveson9}