Abstract
Aims: To assess SARS-CoV-2 seroprevalence over the first epidemic wave in the canton of Geneva, Switzerland, as well as risk factors for infection and symptoms associated with IgG seropositivity. Methods: Between April and June 2020, former participants of a representative survey of the 20–74-year-old population of canton Geneva were invited to participate in the study, along with household members aged over 5 years. Blood samples were tested for anti-SARS-CoV-2 immunoglobulin G. Questionnaires were self-administered. We estimated seroprevalence with a Bayesian model accounting for test performance and sampling design. Results: We included 8344 participants, with an overall adjusted seroprevalence of 7.8% (95% credible interval 6.8–8.9). Seroprevalence was highest among 18–49 year-olds (9.5%), and lowest in 5–9-year-old children (4.3%) and individuals >65 years (4.7-5.4%). Odds of seropositivity were significantly reduced for female retirees and unemployed men compared to employed individuals, and smokers compared to non-smokers. We found no significant association between occupation, level of education, neighborhood income and the risk of being seropositive. The symptom most strongly associated with seropositivity was anosmia/dysgeusia. Conclusions: Anti-SARS-CoV-2 population seroprevalence remained low after the first wave in Geneva. Socioeconomic factors were not associated with seropositivity in this sample. The elderly, young children and smokers were less frequently seropositive, although it is not clear how biology and behaviours shape these differences.
Highlights
Seroprevalence studies around the world have established that only a small proportion of the population had been infected by SARS-CoV-2 towards the end of the first wave in spring 2020, with most seroprevalence estimates ranging from less than 0.1 to more than 20%, depending on the setting and targeted populations [1,2,3]
While working in the healthcare field or essential services has been shown to be associated with a higher risk of seropositivity [6, 7, 14, 16], other individual factors such as education level and occupational category are rarely described.Serosurveys can provide a means to quantify the full spectrum of symptoms associated with SARS-CoV-2, including mild and asymptomatic infections
We describe the agespecific seroprevalence of anti-SARS-CoV-2 antibodies between April and June 2020 in Geneva, Switzerland, and examine risk factors for and symptoms associated with seropositivity
Summary
Seroprevalence studies around the world have established that only a small proportion of the population had been infected by SARS-CoV-2 towards the end of the first wave in spring 2020, with most seroprevalence estimates ranging from less than 0.1 to more than 20%, depending on the setting and targeted populations [1,2,3]. Socioeconomic risk factors for COVID-19 such as low income, social deprivation and overcrowded living conditions have been identified in several studies based on molecular testing [9,10,11,12,13]. Some of those studies included only hospitalised patients or individuals with severe COVID-19. Serosurveys have the potential to assess the real extent of an outbreak in a given geographical region and provide information on risk factors, transmission and infection fatality rates without relying on clinical surveillance and virological confirmation. While working in the healthcare field or essential services has been shown to be associated with a higher risk of seropositivity [6, 7, 14, 16], other individual factors such as education level and occupational category are rarely described.Serosurveys can provide a means to quantify the full spectrum of symptoms associated with SARS-CoV-2, including mild and asymptomatic infections
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