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Original article

Vol. 152 No. 0102 (2022)

High SARS-CoV-2 seroprevalence but no severe course of COVID-19 disease among people on opioid agonist treatment in Zurich: a cross-sectional study

  • Philip Bruggmann
  • Oliver Senn
  • Anja Frei
  • Milo A. Puhan
  • Jan Fehr
  • Luis Falcato
Cite this as:
Swiss Med Wkly. 2022;152:w30122


BACKGROUND AND AIMS: Among people on opioid agonist treatment (OAT), social-environmental and behavioural risk factors may promote the spread of SARS-CoV-2, and somatic comorbidities are highly prevalent. Thus, this population is considered at elevated risk for being infected as well as for developing a more severe course of COVID-19 disease. The aim was to assess the SARS-CoV-2 seroprevalence among people in ongoing OAT, to explore whether the antibody positive group differed from the antibody negative group, and to compare the SARS-CoV-2 seroprevalence among OAT patients with the prevalence in the regional general population.

METHODS: The nationwide Corona Immunitas study assessed the participants’ Sars-CoV-2 antibody status, social characteristics and behavioural data after the first wave of the corona pandemic in Switzerland, between the end of June and beginning of September 2020. We analysed the subsample of OAT patients (n = 122) and the subsample from the general population of the canton of Zurich (n = 472).

RESULTS: SARS-CoV-2 seroprevalence in the general population (mean age ± standard deviation 44.7 ± 11.7 years; 50.9% female) was 3.5% (95% confidence interval [CI] 2.2–4.8%) vs 9.8% (5.1–17.2%) in the OAT population age 44.3 ± 9.4 years; 30.3% female), corresponding to a prevalence ratio of 2.9 (95% CI 1.37–5.94; p = 0.004). OAT patients had a significantly worse health status than the general population. In the OAT group, we found no significant difference between seropositive and seronegative individuals regarding socioeconomic status, risk behaviour, COVID-19-related symptoms or comorbidity. None of the OAT patients who tested positive had a severe course of COVID-19.

CONCLUSION: The 3-fold higher seroprevalence suggests a higher than average viral exposure in the OAT group. Nevertheless, no severe COVID-19 course occurred, although the number of study participants was relatively small. One possible reason for this could be possible cross-immunity to SARS-CoV-2 due to frequent viral contacts in OAT patients. 

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