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SARS-CoV-2 antibody prevalence and correlates of six ethnic groups living in Amsterdam, the Netherlands: a population-based cross-sectional study, June–October 2020

Objectives It has been suggested that ethnic minorities have been disproportionally affected by the COVID-19. We aimed to determine whether prevalence and correlates of past SARS-CoV-2 exposure varied between six ethnic groups in Amsterdam, the Netherlands. Design, setting, participants Participants aged 25–79 years enrolled in the Healthy Life in an Urban Setting population-based prospective cohort (n=16 889) were randomly selected within ethnic groups and invited to participate in a cross-sectional COVID-19 seroprevalence substudy. Outcome measures We tested participants for SARS-CoV-2-specific antibodies and collected information on SARS-CoV-2 exposures. We estimated prevalence and correlates of SARS-CoV-2 exposure within ethnic groups using survey-weighted logistic regression adjusting for age, sex and calendar time. Results Between 24 June and 9 October 2020, we included 2497 participants. Adjusted SARS-CoV-2 seroprevalence was comparable between ethnic Dutch (24/498; 5.1%, 95% CI 2.8% to 7.4%), South-Asian Surinamese (22/451; 4.9%, 95% CI 2.2% to 7.7%), African Surinamese (22/400; 8.3%, 95% CI 3.1% to 13.6%), Turkish (30/408; 7.9%, 95% CI 4.4% to 11.4%) and Moroccan (32/391; 7.2%, 95% CI 4.2% to 10.1%) participants, but higher among Ghanaians (95/327; 26.3%, 95% CI 18.5% to 34.0%). 57.1% of SARS-CoV-2-positive participants did not suspect or were unsure of being infected, which was lowest in African Surinamese (18.2%) and highest in Ghanaians (90.5%). Correlates of SARS-CoV-2 exposure varied across ethnic groups, while the most common correlate was having a household member suspected of infection. In Ghanaians, seropositivity was associated with older age, larger household sizes, living with small children, leaving home to work and attending religious services. Conclusions No remarkable differences in SARS-CoV-2 seroprevalence were observed between the largest ethnic groups in Amsterdam after the first wave of infections. The higher infection seroprevalence observed among Ghanaians, which passed mostly unnoticed, warrants wider prevention efforts and opportunities for non-symptom-based testing.

The Healthy life in an Urban Setting (HELIUS) study is a large, population-based cohort study 97 among six different ethnic groups, which was established with the aim to investigate mechanisms 98 underlying the impact of ethnicity on communicable and non-communicable diseases. [9] From 99 individuals actively enrolled in this study, we determined the prevalence and determinants of 100 exposure to SARS-CoV-2 between the largest ethnic groups in Amsterdam. 101

Methods
Outcomes 127 SARS-CoV-2 exposure was determined by the presence of SARS-CoV-2 antibodies. SARS-CoV-2-128 specific antibodies were determined using the WANTAI SARS-CoV-2 Ab Elisa (Wantai Biological 129 Pharmacy Enterprise Co., Beijing, China) according to the manufacturer's instructions. This Elisa 130 detects IgA, IgM and IgG against the receptor binding domain of the S-protein of SARS-CoV-2.
[10] 131 Determinants 132 We defined the following potential determinants: from the baseline visit of the HELIUS study-133 demographics (i.e. age, sex, ethnicity, migration generation, city district), socio-economic factors 134 (i.e. educational level, working status, occupational level, number of people in household), access-135 to-healthcare indicators (i.e. proficiency with Dutch language, health literacy); from the COVID-19 136 substudy visit-job setting, household members, suspected being infected, thinking household 137 member/steady partner was infected, household member hospitalized for COVID-19, type of 138 people living in household, travelling abroad in 2020 and COVID-19 behaviors in the past week (i.e. 139 number of times leaving the house, type of locations visited, number of visitors, frequency of using 140 public transportation). 141 Statistical analysis 142 literacy). The product of the two probabilities was taken and the inverse of this result, standardized 152 to one, was used as a sampling weight. For post-stratification, a weight was assigned corresponding 153 to the proportion representing the Amsterdam population of each stratum of age (20-44, 45-54, 55-154 59, 60-79 years), sex (male, female) and ethnicity (Surinamese,Ghanaian,Moroccan,Turkish,155 Dutch). Sampling and post-stratification weights were placed in a multivariable logistic regression 156 model with covariates ethnicity, age, sex, and calendar time. Given the weighting scheme of this 157 study, variance was calculated with the designed-based Taylor series linearization method using the 158 'svy' commands in STATA. Differences between ethnic groups were tested in the model using the 159 Wald χ2 test. 160 Seroprevalence was regressed on age (in restricted cubic splines with 3 knots) with sample and 161 post-stratification weights, within subpopulations of ethnic groups. The mean and 95%CI of 162 predicted seroprevalence was plotted over age in years. 163 To identify determinants of past SARS-CoV-2 infection within ethnic groups, univariable 164 associations between potential determinants and SARS-CoV-2 seropositivity were evaluated. The 165 odds ratios (OR) comparing the odds of seroprevalence across levels of each determinant, and their 166 95% confidence intervals (CI), were estimated using logistic regression. P-values were obtained 167 using the Wald χ 2 test. All covariates with a P-value≤0.2 in univariable analyses were then included 168 in a multivariable model and after assessing covariate distributions and collinearity, variables with a

Study population 176
Of the 16,889 HELIUS participants who were in active follow-up in 2019-2020, 11,080 (65.6%) were 177 invited ( Figure 1). Of these, 2497 (22.5%) were included in the COVID-19 substudy. The response 178 rate varied across ethnic groups, from 15.3-17.2% among Ghanaian, Turkish or Moroccan 179 participants to 49.9% among Dutch participants. Detailed information on differences between 180 HELIUS participants who were and were not invited, and between invited participants who were 181 and were not included, are presented in Supplementary Table 1. Briefly, invited individuals who 182 were included had obtained a slightly higher educational level, were more likely to be employed and 183 were more likely to have adequate health literacy level compared to those who were invited but not 184

included. 185
Number included per month within ethnic groups is presented in Supplementary Figure 1   95%CI=3.2-7.9), South-Asian Surinamese (4.8%, 95%CI=2.1-7.5), African Surinamese (8.2%, 202 95%CI=3.0-13.4), Turkish (7.8%, 95%CI=4.3-11.2) and Moroccan (7.0%, 95%CI=4.0-9.9) groups, but 203 higher in the Ghanaian group compared to all other groups (26.5%, 95%CI=18.7-34.4, P<0.001). 204 Figure 3 shows adjusted seroprevalence estimates as a function of age in years for each ethnic 205 group. In the African Surinamese group, seroprevalence decreased with age. In the Ghanaian group, 206 the highest seroprevalence was observed between the ages of 50-55 years. 207 Table 2  Strikingly, 90% of Ghanaians with SARS-CoV-2 antibodies did not suspect or were unsure of being 258 infected, many because they did not report experiencing any COVID-19-related symptoms. This is Since data from Ghana on SARS-CoV-2 seroprevalence and proportion of asymptomatic infection 272 are limited, we cannot make any distinction on whether our finding reflects the epidemiology in the 273 country of origin or is specific to Ghanaian individuals in the Netherlands. One modelling study 274

COVID-19-related symptoms 208
suggests that Ghana is one of the four most affected African countries in terms of cases, but has a 275 relatively low death rate. [ about their health compared to non-participants. Notwithstanding the differential response rate 313 between ethnicities in this substudy, the distribution of characteristics was largely similar between 314 included and non-included HELIUS participants. Our estimates, corrected for sampling and post-315 stratification, were also close to those from a nationwide study that included mainly people of 316 Dutch origin and revealed a 6% seroprevalence among the Amsterdam population in June 2020.
[35] 317 Data were also collected over a span of 4 months, which reflects different points of the epidemic, 318 and thus the timing of testing could bias estimates. We attempted to mitigate this issue by 319 adjusting for calendar time. Furthermore, prevention measures remained mostly the same and 320 nationwide incidence was quite stable during this period, thereby limiting the effect of this 321 bias. [8,36] Third, as this study was cross-sectional and infection occurred in the past, it is difficult to 322 make any causal inference with respect to determinants. Fourth, fear of stigmatization or 323 consequences for work might have led to an underreporting of suspected past infection and 324 symptoms, particularly among Ghanaians. Finally, circulating SARS-CoV-2 antibodies could have 325 disappeared after infection, [37,38] although this was probably limited during the study In conclusion, most ethnic groups displayed comparable seroprevalence after the first SARS-CoV-2 329 wave in Amsterdam, yet the substantially higher prevalence among the smaller Ghanaian 330 population, possibly infections without symptoms, is of concern. Targeted prevention campaigns 331 addressing the needs of specific ethnic groups and expanding testing opportunities are urgently 332 warranted. In addition, prevention measures for those who cannot work from home should be 333 intensified, also by bringing to light the employer's role in reducing COVID-19 transmissions.

Declaration of interests 339
The authors declare that they have no competing interests related to the project. 340

341
The HELIUS data are owned by the Amsterdam UMC, location AMC, in Amsterdam, The 342 Netherlands. Any researcher can request the data by submitting a proposal to the HELIUS 343 Executive Board as outlined at http://www.heliusstudy.nl/en/researchers/collaboration, by email: 344 heliuscoordinator@amsterdamumc.nl. The HELIUS Executive Board will check proposals for 345 compatibility with the general objectives, ethical approvals and informed consent forms of the 346 HELIUS study. There are no other restrictions to obtaining the data and all data requests will be 347 processed in the same manner. 348 The authors would like to acknowledge the HELIUS COVID-19 study participants for their 357 contribution and the HELIUS team for data collection and management. They would also like to 358 thank Anton Janssen for providing population tables. 359

10.
GeurtsvanKessel    Footnote: We excluded individuals with an equivocal result (n=8) from the seroprevalence 488 calculation. Boxes represent the seroprevalence estimate, bands the corresponding 95% confidence 489 interval. Adjusted seroprevalence estimates were corrected for sampling, accounted for the 490 population structure of ethnic groups in Amsterdam (i.e. post-stratification), and adjusted for 491 differences in age, sex and calendar time (before/after 15 August 2020) between ethnic groups. 492