Prevalence of SARS-CoV-2 antibodies in New York City adults, June–October, 2020: a population-based survey

Abstract Background Serosurveys are important to ascertain burden of infection. Prior SARS-CoV-2 serosurveys in New York City (NYC) have used nonrandom samples. During June–October 2020, the NYC Health Department conducted a population-based survey to estimate SARS-CoV-2 antibody prevalence in NYC adults. Methods Participants were recruited from the NYC 2020 Community Health Survey. We estimated citywide and stratified antibody prevalence using a hybrid design: serum tested at the NYC Health Department using the DiaSorin LIAISON ® SARS-CoV-2 S1/S2 IgG assay and self-reported antibody test results were used together. Prevalence was estimated using univariate frequencies and 95% confidence intervals (CI), accounting for complex survey design. Two-sided P-values ≤0.05 were statistically significant. Results There were 1074 respondents overall; 497 provided blood and 577 provided only a self-reported antibody test result. Weighted prevalence was 24.3% overall (95% CI: 20.7–28.3). Latino (30.7%, 95% CI: 24.1–38.2, p<0.01) and Black (30.7%, 95% CI: 21.9–41.2, p=0.02) respondents had a higher weighted prevalence compared with White respondents (17.4%, 95% CI: 12.5–23.7). Conclusions By October 2020, nearly 1 in 3 Black and 1 in 3 Latino NYC adults had SARS-CoV-2 antibodies, highlighting unequal impacts of the COVID-19 pandemic on Black and Latino adults in NYC.

A c c e p t e d M a n u s c r i p t

Specimen Collection and Testing
For each consenting participant, a phlebotomist conducted an at-home blood draw to collect 5 ml of whole blood in a serum separator tube. On the same day, samples were transported at 4°C to the NYC Public Health Laboratory where serum was separated from the specimen and tested for SARS-CoV-2 IgG antibodies using the DiaSorin LIAISON ® SARS-CoV-2 S1/S2 IgG assay [12]. The test has a reported 97.6% positive and 99.3% negative percent agreement with RT-PCR testing at the time of infection [12].
Peer reviewed literature on this assay described specificity ranging from 90.5% to 98.9% with varying sensitivity depending on the timeframe of antibody detection after positive PCR test for SARS-CoV-2 [13][14][15].
The NYC DOHMH Institutional Review Board determined this as public health surveillance. The Centers for Disease Control and Prevention (CDC) reviewed this activity; it was conducted consistent with applicable federal law and CDC policy.  Informed consent was obtained from participants before specimen collection.

Power Calculations
Power calculations were performed using population estimates from the 2019 CHS to assure ability to reliably detect antibody prevalence. We calculated the sample size necessary to achieve a relative standard error (RSE) <0.30 for a range of hypothetical prevalence rates of 5-30%. For our survey, an RSE >0. 30 indicates an estimate is potentially unreliable. Accounting for survey design artifacts and assuming ≥10% antibody prevalence, with 1000 participants, we could make a citywide antibody prevalence estimate with a RSE <0. 30. Assuming ≥15% antibody prevalence, with 2200 participants, we A c c e p t e d M a n u s c r i p t 6 could make antibody prevalence estimates stratified by race/ethnicity with a RSE <0. 30 for White, Black, and Latino New Yorkers. We aimed to recruit between 1000-2200 participants with the knowledge that with higher antibody prevalence, a smaller sample size would be necessary to achieve a stable estimate overall or in stratified analyses.

Data Analysis
To generate a representative estimate of antibody prevalence among the NYC non-institutionalized adult residential population, CHS data were weighted adjusting for varying selection probabilities and potential overlapping landline and cell phone sampling frames. Survey weights were adjusted to 20142018 ACS [11] population control totals using SAS code rake_and_trim_G4_V5.sas [16]; final weights were scaled to adjust for potential nonresponse bias.
We used American Association for Public Opinion Research standard definitions (revised 2016) to calculate annual CHS Cooperation Rate #3 and Response Rate #3 [17]. Cooperation Rate #3 is the number of survey participants, divided by the number in the sample who were contacted and determined as eligible. Response Rate #3, a more conservative estimate, is the number of survey participants who complete the survey, divided by those who completed plus partial completes, refusals, non-contacts, and cases of unknown eligibility. People with unknown eligibility lacked live contact by an interviewer to determine eligibility. These could have included business or non-working numbers (both ineligible).
People with unknown eligibility typically comprise most of the denominator; the denominator was adjusted to estimate the proportion of unknown but likely to be eligible people. The 2020 CHS cooperation and response rates were 74.4% and 7.4%, respectively.
A c c e p t e d M a n u s c r i p t 7 Univariate prevalence estimates and 95% confidence intervals (CI) were generated. Combined antibody test results, including self-reported test results, were used for all analyses to estimate citywide and stratified prevalence. For those who provided both a blood specimen and a self-reported test result, only serosurvey specimens tested by DOHMH were used in analyses. Data were stratified by demographics. Ttests were used to compare antibody prevalence by sex, age, race/ethnicity, borough of residence, place of birth, language of interview, neighborhood poverty level, and health insurance status. We assessed estimate reliability based on RSE, sample size, and CI width. To determine if prevalence differed between the two groups, a multivariable logistic regression model was constructed to see if there were increased odds of having a positive test result if the respondent self-reported versus provided a blood specimen for the serosurvey, while controlling for sex, race/ethnicity, age, borough of residence, language of interview, and neighborhood poverty level. We used SAS EG v7.15 and SUDAAN 11.0.1 accounting for weight and complex survey design. Two-sided P-values ≤0.05 were statistically significant.
The overall weighted SARS-CoV-2 antibody prevalence, including those who provided a blood specimen and those who only provided a self-reported result, was 24  Ninety-one respondents provided both a blood sample and self-reported antibody result. Among these, 81 had concordant results (89.0%), and ten (11.0%) had discordant results: four respondents self-reported a positive test result and were negative for antibodies upon testing; six respondents self-reported a negative test result and were positive for antibodies upon testing.
When examining combined weighted results from the serological tests and self-reported data, antibody prevalence was similar by sex. Respondents aged 18-44 years had higher prevalence ( A c c e p t e d M a n u s c r i p t 9 Antibody prevalence varied among respondents with different underlying conditions. Respondents with asthma had a lower prevalence than those without it (11.7%, 95% CI: 6.6-19.9, p<0.001 vs 26 (Table 3).
Antibody prevalence was significantly greater, more than three times higher, among respondents who reported COVID-19-like illness symptoms at some point between February 2020 until survey administration (43.6%, 95% CI: 36.7-50.7, p<0.001) compared with those who did not report any of these symptoms (13.0%, 95% CI: 9.3-17.9). People who thought they had experienced COVID-19 (not mutually exclusive with those who reported COVID-19-like illness) had higher prevalence (81.2%, 95% CI: 72.8-87.4, p<0.001) compared with those who did not think they had COVID-19 (9.5%, 95% CI: 6.5-13.6) ( Table 4). Respondents who worked mostly outside the home had a higher prevalence compared with those who worked mostly from within the home. As Black and Latino people are overrepresented in several essential industries, workplace related exposures might be contributing to higher antibody prevalence among Black and Latino respondents [6,29]. Overall, our findings illustrate how the COVID-19 pandemic unequally impacted NYC residents, with Black and Latino New Yorkers and those from poorer neighborhoods more A c c e p t e d M a n u s c r i p t 11 likely to have had previous SARS-CoV-2 infection. These inequities result from myriad structural, racial, and economic inequalities that drive NYC health disparities [25, 2830].
Our combined weighted citywide seroprevalence estimate is consistent with New York State Health Department data of NYC residents visiting grocery stores, which found 22.7% seropositivity during April 19-28, 2020 [4]. A cross-sectional serosurvey of routine care patients at Mt Sinai Hospital in NYC found 19.1% prevalence in the week ending on April 19, and up to 61.7% among urgent care patients [5]. A NYC Serosurvey of adult residents found a 23.6% prevalence from May 13-July 21,2020 [6]. Using residual commercial laboratory specimens, a CDC nationwide serosurvey estimated 25.1% of metro New York residents had antibodies during July 27-August 13, 2020, similar to our citywide estimate [20].
While prior studies differ in methodology and sample, our study provides important confirmation of prior estimates in NYC during this time and also offers the ability to examine estimates based on demographic and socioeconomic variables.
We chose to conduct phlebotomy in participants" homes to reduce potential biases associated with sampling in specific locations that would require participants to travel to or only testing persons potentially more likely to be ill. Home specimen collection enabled us to include respondents who lacked access to transportation or health care, or who were uncomfortable leaving their home during the pandemic. We combined antibody test results for this survey with self-reported antibody results collected via telephone survey to increase our sample size to estimate stratified antibody prevalence with greater precision. Including self-reported test results also helped to minimize selection bias in two ways. First, it included individuals who previously had an antibody test and didn"t want the test to be repeated. During the time of this serosurvey, antibody testing was publicly available including at several city-run mass serology sites and some people didn"t want to undergo repeat phlebotomy. Second, including selfreported results allowed us to survey individuals who preferred not having a phlebotomist visit their home during a pandemic, which was a common reason respondents declined specimen collection. While A c c e p t e d M a n u s c r i p t 12 controlling for demographic variables, we found that respondents with only self-reported results had elevated yet non-significant odds of having a positive result compared with respondents that provided blood. We hypothesize that individuals who self-reported a positive antibody test might have been less inclined to repeat serology compared with those who self-reported a negative antibody test. While initially SARS-CoV-2 seroprevalence was believed to be a proxy for cumulative infections [9], it is now well-documented that individuals with asymptomatic or mild SARS-CoV-2 infections might not produce antibodies, have limited antibody response, or have waning antibodies [20,34,36]. Other studies have tracked the decline in seroprevalence in NYC from April to July 2020 [5,7]. Our survey did not require respondents with self-reported antibody results to recall the date of their previous antibody testing, nor the manufacturer of the serological assay. Survey respondents who self-reported a test result that was conducted between March 2020, when commercial SARS-CoV-2 assays became available [37], and our study period in June 2020, might have included individuals who were positive at the time of testing but seroconverted by June. Our antibody prevalence estimates likely underestimate cumulative infections overall; however, the self-reported data might overestimate antibody prevalence by including individuals who by June through October were no longer antibody positive. Additionally, considering the varied performance of different SARS-CoV-2 serologic assays, respondents with self-reported antibody results A c c e p t e d M a n u s c r i p t 13 might have been tested with a low performing assay, increasing potential for false positive or negative test results [37].
Telephone survey response rates have been declining for years, which is consistent with the low 2020 CHS response rate [38]. One limitation of a low response is the potential for non-response bias; the prevalence among those that declined survey participation is unknown. While declining survey response rates indicate potential nonresponse bias, they are not a direct measure of nonresponse bias [39].
Additional limitations include the following: aside from respondents who provided both a specimen and self-reported result, the remaining self-reported test results were not further verified, so recall bias could not be assessed. Among those who provided a blood specimen, the median time between survey administration and blood draw was 16 days. Some subgroups with small sample sizes should be interpreted with caution. Finally, this survey included only non-institutionalized adults; results cannot be extrapolated to other populations like children or those residing in congregate settings.
At the population level, representative cross-sectional surveys provide important data about the extent of the pandemic. While other research is ongoing to understand immunity against the SARS-CoV-2 virus, our population-based prevalence estimates help inform an understanding of which NYC populations are most at risk and those that might still be susceptible to SARS-CoV-2 infection. This work offers an important baseline of SARS-CoV-2 antibody prevalence in NYC following the first wave of the COVID-M a n u s c r i p t M a n u s c r i p t M a n u s c r i p t    A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t 9.5 6.5-13.6 ref a Missing data were excluded from analysis so co-variates do not always sum to 1074. b Antibody prevalence was estimated accounting for complex survey design and weighting to the NYC adult residential population.
c Estimate should be interpreted with caution. Estimate's relative standard error (a measure of estimate precision) is greater than 30%, or the 95% confidence interval half-width is greater than 10 or the sample size is too small, making the estimate potentially unreliable.
d Respondents were asked about experiencing symptoms indicative of COVID-19-like illness in the past 30 days. If respondents did not experience any symptoms indicative of COVID-19-like illness in the past 30 days, they were asked "Since February 2020 until now, do you remember if you experienced any of the following? A fever, cough, shortness of breath, sore throat, or loss of taste or loss of smell?" (N=993). e Respondents who experienced symptoms of COVID-19-like illness in the past 30 days were asked whether or not they believed the symptoms were associated with COVID-19 infection. If respondents did not experience any symptom of COVID-19-like illness in the past 30 days, or if they did not think they had COVID-19 within the past 30 days, they were asked "Since February 2020 until now, do you think you may have had the Coronavirus or COVID-19?" (N=986).