Seroprevalence of anti-SARS-CoV-2 IgG antibodies, risk factors for infection and associated symptoms in Geneva, Switzerland: a population-based study

Abstract

BackgroundPopulation-based serological surveys provide a means for assessing the immunologic landscape of a community, without the biases related to health-seeking behaviors and testing practices typically associated with rt-PCR testing. This study assesses SARS-CoV-2 seroprevalence over the first epidemic wave in Canton Geneva, Switzerland, as well as biological and socio-economic risk factors for infection and symptoms associated with IgG seropositivity.Methods and findingsBetween April 6 and June 30, 2020, former participants of a yearly representative cross-sectional survey of the 20-75-year-old population of the canton of Geneva were invited to participate in a seroprevalence study, along with household members five years and older. We collected blood and tested it for anti-SARS-CoV-2 immunoglobulins G (IgG). Questionnaires were self-administered. We estimated seroprevalence with a Bayesian model accounting for test performance and sampling design. We included 8344 participants (53.5% women, mean age 46.9 years). The population-level seroprevalence over the 12-week study period was 7.8 % (95% Credible Interval (CrI) 6.8-8.9), accounting for sex, age and household random effects. Seroprevalence was highest among 18-49 year olds (9.5%, 95%CrI 8.1-10.9), with young children (5-9 years) and those >65 years having significantly lower seroprevalence (4.3% and 4.7-5.4% respectively). Men were more likely to be seropositive than women (relative risk 1.2, 95%CrI 1.1-1.4). Odds of seropositivity were reduced for female retirees (0.46, 95%CI 0.23-0.93) and unemployed men (0.35, 95%CI 0.13-1.0) compared to employed individuals, and for current smokers (0.36, 95%CI 0.23-0.55) compared to never-smokers. We found no significant association between occupation, level of education, neighborhood income and the risk of being seropositive. Symptoms most strongly associated with seropositivity were anosmia/dysgeusia, loss of appetite, fever, fatigue and myalgia and/or arthralgia. Thirteen percent of seropositive participants reported no symptoms.ConclusionsOur results confirm a low population seroprevalence of anti-SARS-CoV-2 antibodies after the first wave in Geneva, a region hard hit by the COVID-19 pandemic. Socioeconomic factors were not associated with seropositivity in this sample. The elderly and young children were less frequently seropositive, though it is not clear how biology and behaviors shape these differences. These specificities should be considered when assessing the need for targeted public health measures.

Large variation in anti-SARS-CoV-2 antibody prevalence among essential workers in Geneva, Switzerland

“…In this large sample of workers from 16 sectors who were mobilized during the spring 2020 Swiss lockdown, we observed that the proportion of workers having developed anti-SARS-CoV-2 antibodies after the first COVID-19 wave varied widely across sectors, across facilities within sectors and across occupations within sectors. With few important exceptions, our findings do not show a pattern of increased risk of SARS-CoV-2 infection among sectors and occupations of workers who were mobilized during the lockdown, the overall seropositivity rate of this sample being only slightly higher than that of the general working-age population during the spring 2020 21 . Yet, there was considerable variability across sectors and occupations.…”

“…Overall, 9.8% of individuals (1026/10513) tested positive for SARS-CoV-2 anti-S1 IgG antibodies (Table 1), roughly the same seropositivity rate (7.9% [95% CrI: 6.8-8.9]) as the general working-age population of Geneva over a similar time period 21 . Older participants (≥50 years) had a lower risk of being seropositive (RR: 0.70; 95% CrI: 0.56-0.83) compared with 18-34year-old participants.…”

“…The canton of Geneva in Switzerland reported its first confirmed COVID-19 case on February 26, 2020, and by April 26, 2021, 54,964 confirmed cases (110.0 per 1000 inhabitants) and 729 deaths had been reported 19 . Lockdown measures-similar to those implemented regionally or nationally across Europe and North America-were imposed on March 16, 2020 from which only essential businesses remained operational and the population was encouraged to stay home; progressive lifting of restrictions took place from April 27, 2020 until June 6, 2020.To understand the SARS-CoV-2 infection risk among workers from key sectors that remained operational during the lockdown, we established the SEROCoV-WORK + serology study, using the same testing procedure as in our SEROCoV-POP populationbased seroprevalence study 20,21 , whose representative sample can serve as comparison.…”

Serological evidence of human infection with SARS-CoV-2: a systematic review and meta-analysis

“…Values higher than 1 suggest greater under-reporting of infections (due to both mild or asymptomatic infections, care-seeking behaviours, and testing practices). 27 USA, California, Marin (Appa et al 2020) 28 USA, California, Orange (Bruckner et al 2021) 29 USA, Connecticut (Mahajan et al 2020) 30 USA, Georgia, DeKalb and Fulton (Biggs et al 2020) 31 USA, Idaho, Blaine (McLaughlin et al 2020) 32 USA, Utah, four counties (Samore et al 2020) 33 Denmark, Faroe Islands (Petersen et al 2020) 34 Germany, Kreis Heinsberg, Gangelt (Streeck et al 2020) 35 Luxembourg (Snoeck et al 2020) 36 Netherlands (Vos et al 2020) 37 Russia, Saint Petersburg (Barchuk et al 2020) 38 Spain (Pollán et al 2020) 39 Switzerland, Geneva (Richard et al 2020) 40 Switzerland, Geneva (Stringhini et al 2020) 41 UK, England (Office of National Statistics 2020) 42 UK, England (Ward et al 2020) 43 UK, Jersey (Government of Jersey 2020) 44 India (Murhekar et al 2020 ) 45 India (Murhekar et al 2021) 46 India, Delhi (Sharma et al 2020) 47 India, Mumbai (Malani et might lead to mis-specification of assay performance. 53 Notably, although WHO has established a generic population-based serological study protocol, standardised guidelines and procedures for laboratory testing are scarce, which might contribute towards such heterogeneity in performance and reporting of results.…”

The association of smoking status with SARS-CoV-2 infection, hospitalisation and mortality from COVID-19: A living rapid evidence review with Bayesian meta-analyses (version 11)

“…We identified one population study conducted in Hungary reporting on seroprevalence and smoking status (Merkely et al, 2020); however, the response rate was only 58.8% and the current smoking rate was 10 percentage points below national prevalence estimates, which raises some doubt about representativeness of the final sample. Similarly, two further representative population surveys (Carrat et al, 2020;Richard et al, 2020)…”