Skip to main navigation menu Skip to main content Skip to site footer

Original article

Vol. 151 No. 3334 (2021)

Seroprevalence of SARS-CoV-2 in healthcare workers from outpatient facilities and retirement or nursing homes in a Swiss canton

  • Kathrin Zürcher 
  • Catrina Mugglin 
  • Franziska Suter-Riniker 
  • Peter M. Keller
  • Matthias Egger 
  • Sandro Müller 
  • Michael Fluri
  • Matthias Hoffmann 
  • Lukas Fenner
Cite this as:
Swiss Med Wkly. 2021;151:w30021


BACKGROUND: Healthcare workers are more frequently exposed to SARS-CoV-2 than the general population. Little is known about healthcare settings outside of hospitals. We studied the seroprevalence of SARS-CoV-2 among healthcare workers in outpatient facilities and retirement or nursing homes in the Canton of Solothurn, Switzerland in the first wave of the COVID-19 pandemic.

METHODS: Longitudinal seroprevalence study among healthcare workers with examinations at baseline and 2 months between June and September 2020. The Abbott SARS-CoV-2 IgG and Liaison/Diasorin SARS-CoV-2 S1/S2 IgG assay were used to detect antibodies against SARS-CoV-2. All participants provided demographic information. We report descriptive statistics and calculated the seroprevalence with 95% confidence intervals.

RESULTS: We included 357 healthcare workers; their median age was 43 years (interquartile range 29–54), and 315 (88.2%) were female. Forty-nine (13.7%) were physicians, 87 (24.4%) practice assistants and 221 (61.9%) nurses. Overall seroprevalence among healthcare workers in outpatient facilities and retirement or nursing homes was 3.4% (12/357). The 12 seropositive healthcare workers were all nurses (12/221, 5.5%); 11 worked at retirement or nursing homes and one at the hospital's outpatient clinic. Symptoms such as loss of smell or taste, shortness of breath, and fever were more prevalent among seropositive healthcare workers than seronegative healthcare workers. No close contact had detectable antibodies against SARS-CoV-2.

CONCLUSIONS: Seroprevalence among healthcare workers was low, but higher among nursing staff of retirement or nursing homes. Healthcare workers at private practices were able to protect themselves well during the first wave of the COVID-19 pandemic.


  1. Federal Office of Public Health (FOPH). Coronavirus: Situation in Switzerland Bern: Federal Office of Public Health (FOPH); 2020 Available from:
  2. Garcia-Basteiro AL, Moncunill G, Tortajada M, Vidal M, Guinovart C, Jiménez A, et al. Seroprevalence of antibodies against SARS-CoV-2 among health care workers in a large Spanish reference hospital. Nat Commun. 2020 Jul;11(1):3500.
  3. Folgueira MD, Muñoz-Ruipérez C, Alonso-López MÁ, Delgado R. SARS-CoV-2 infection in Health Care Workers in a large public hospital in Madrid, Spain, during March 2020. medRxiv. 2020:20055723. doi:
  4. Lombardi A, Mangioni D, Consonni D, Cariani L, Bono P, Cantù AP, et al. Seroprevalence of anti-SARS-CoV-2 IgG among healthcare workers of a large university hospital in Milan, Lombardy, Italy: a cross-sectional study. BMJ Open. 2021 Feb;11(2):e047216.
  5. Piccoli L, Ferrari P, Piumatti G, Jovic S, Rodriguez BF, Mele F, et al. Risk assessment and seroprevalence of SARS-CoV-2 infection in healthcare workers of COVID-19 and non-COVID-19 hospitals in Southern Switzerland. Lancet Reg Health Eur. 2021 Feb;1:100013.
  6. Corman VM, Landt O, Kaiser M, Molenkamp R, Meijer A, Chu DK, et al. Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR. Euro Surveill. 2020 Jan;25(3):
  7. Bonelli F, Sarasini A, Zierold C, Calleri M, Bonetti A, Vismara C, et al. Clinical and Analytical Performance of an Automated Serological Test That Identifies S1/S2-Neutralizing IgG in COVID-19 Patients Semiquantitatively. J Clin Microbiol. 2020 Aug;58(9):e01224–20.
  8. Bryan A, Pepper G, Wener MH, Fink SL, Morishima C, Chaudhary A, et al. Performance Characteristics of the Abbott Architect SARS-CoV-2 IgG Assay and Seroprevalence in Boise, Idaho. J Clin Microbiol. 2020 Jul;58(8):e00941–20.
  9. Guo L, Ren L, Yang S, Xiao M, Chang D, Yang F, et al. Profiling Early Humoral Response to Diagnose Novel Coronavirus Disease (COVID-19). Clin Infect Dis. 2020 Jul;71(15):778–85.
  10. Roche. Elecsys® Anti-SARS-CoV-2 Immunoassay for the quantitative determination of antibodies to the SARS-CoV-2 spike protein Switzerland. Roche Diagnostics International Ltd; 2020. Available from: file:///C:/Users/KZUERC~1/AppData/Local/Temp/Elecsys-Anti-SARS-CoV-2-S-factsheet-SEPT-2020-2-1.pdf.
  11. Choe PG, Kim KH, Kang CK, Suh HJ, Kang E, Lee SY, et al. Antibody Responses 8 Months after Asymptomatic or Mild SARS-CoV-2 Infection. Emerg Infect Dis. 2021 Mar;27(3):928–31.
  12. Harris PA, Taylor R, Thielke R, Payne J, Gonzalez N, Conde JG. Research electronic data capture (REDCap)—a metadata-driven methodology and workflow process for providing translational research informatics support. J Biomed Inform. 2009 Apr;42(2):377–81.
  13. Harris PA, Taylor R, Minor BL, Elliott V, Fernandez M, O’Neal L, et al.; REDCap Consortium. The REDCap consortium: building an international community of software platform partners. J Biomed Inform. 2019 Jul;95:103208.
  14. Arons MM, Hatfield KM, Reddy SC, Kimball A, James A, Jacobs JR, et al.; Public Health–Seattle and King County and CDC COVID-19 Investigation Team. Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility. N Engl J Med. 2020 May;382(22):2081–90.
  15. Graham NS, Junghans C, Downes R, Sendall C, Lai H, McKirdy A, et al. SARS-CoV-2 infection, clinical features and outcome of COVID-19 in United Kingdom nursing homes. J Infect. 2020 Sep;81(3):411–9.
  16. McMichael TM, Currie DW, Clark S, Pogosjans S, Kay M, Schwartz NG, et al.; Public Health–Seattle and King County, EvergreenHealth, and CDC COVID-19 Investigation Team. Epidemiology of Covid-19 in a Long-Term Care Facility in King County, Washington. N Engl J Med. 2020 May;382(21):2005–11.
  17. Geschwindner H, Bieri-Brüning G. Covid-19: prevention and outbreak management in nursing homes: experiences from the nursing homes of the city of Zurich. Journal of Nursing Home Research. 2020.
  18. Goldberg SA, Pu CT, Thompson RW, Mark E, Sequist TD, Grabowski DC. Asymptomatic Spread of COVID-19 in 97 Patients at a Skilled Nursing Facility. J Am Med Dir Assoc. 2020 Jul;21(7):980–1.
  19. Guery R, Delaye C, Brule N, Nael V, Castain L, Raffi F, et al. Limited effectiveness of systematic screening by nasopharyngeal RT-PCR of medicalized nursing home staff after a first case of COVID-19 in a resident. Med Mal Infect. 2020 Nov;50(8):748–50.
  20. Roxby AC, Greninger AL, Hatfield KM, Lynch JB, Dellit TH, James A, et al. Detection of SARS-CoV-2 Among Residents and Staff Members of an Independent and Assisted Living Community for Older Adults - Seattle, Washington, 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr;69(14):416–8.
  21. World Health Organization. Preventing and managing COVID-19 across long-term care services: policy brief. Geneva: World Health Organization; 2020.
  22. Smith PW, Bennett G, Bradley S, Drinka P, Lautenbach E, Marx J, et al.; SHEA; APIC. SHEA/APIC guideline: infection prevention and control in the long-term care facility, July 2008. Infect Control Hosp Epidemiol. 2008 Sep;29(9):785–814.
  23. Zúñiga F, Favez L. SHURP 2018 Infektionskontrolle - Resultate zu Handen Strategie NOSO. 2020.
  24. Houghton C, Meskell P, Delaney H, Smalle M, Glenton C, Booth A, et al. Barriers and facilitators to healthcare workers’ adherence with infection prevention and control (IPC) guidelines for respiratory infectious diseases: a rapid qualitative evidence synthesis. Cochrane Database Syst Rev. 2020 Apr;4(4):CD013582.
  25. Leiss JK. Safety climate and use of personal protective equipment and safety medical devices among home care and hospice nurses. Ind Health. 2014;52(6):492–7.
  26. Gómez-Ochoa SA, Franco OH, Rojas LZ, Raguindin PF, Roa-Díaz ZM, Wyssmann BM, et al. COVID-19 in Health-Care Workers: A Living Systematic Review and Meta-Analysis of Prevalence, Risk Factors, Clinical Characteristics, and Outcomes. Am J Epidemiol. 2021 Jan;190(1):161–75.
  27. Rostami A, Sepidarkish M, Leeflang MM, Riahi SM, Nourollahpour Shiadeh M, Esfandyari S, et al. SARS-CoV-2 seroprevalence worldwide: a systematic review and meta-analysis. Clin Microbiol Infect. 2021 Mar;27(3):331–40.
  28. Rudberg AS, Havervall S, Månberg A, Jernbom Falk A, Aguilera K, Ng H, et al. SARS-CoV-2 exposure, symptoms and seroprevalence in healthcare workers in Sweden. Nat Commun. 2020 Oct;11(1):5064.
  29. Thompson HA, Mousa A, Dighe A, Fu H, Arnedo-Pena A, Barrett P, et al. SARS-CoV-2 setting-specific transmission rates: a systematic review and meta-analysis. Clin Infect Dis. 2021 Aug;73(3):e754–64.
  30. Zhao D, Wang M, Wang M, Zhao Y, Zheng Z, Li X, et al. Asymptomatic infection by SARS-CoV-2 in healthcare workers: A study in a large teaching hospital in Wuhan, China. Int J Infect Dis. 2020 Oct;99:219–25.
  31. Buitrago-Garcia D, Egli-Gany D, Counotte MJ, Hossmann S, Imeri H, Ipekci AM, et al. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. PLoS Med. 2020 Sep;17(9):e1003346.
  32. Canova V, Lederer Schläpfer H, Piso RJ, Droll A, Fenner L, Hoffmann T, et al. Transmission risk of SARS-CoV-2 to healthcare workers -observational results of a primary care hospital contact tracing. Swiss Med Wkly. 2020 Apr;150:w20257.

Most read articles by the same author(s)