Disparities in SARS-CoV-2 exposure: evidence from a citywide seroprevalence study in Holyoke, Massachusetts, USA

  1. Wilfredo R. Matias
  2. Isabel R. Fulcher
  3. Sara M. Sauer
  4. Cody P. Nolan
  5. Yodeline Guillaume
  6. Jack Zhu
  7. Francisco J. Molano
  8. Elizabeth Uceta
  9. Shannon Collins
  10. Damien M. Slater
  11. Vanessa M. Sánchez
  12. Serina Moheed
  13. Jason B. Harris
  14. Richelle C. Charles
  15. Ryan M. Paxton
  16. Sean F. Gonsalves
  17. Molly F. Franke
  18. Louise C. Ivers

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Abstract

Background

Seroprevalence studies are important tools to estimate the prevalence of prior or recent SARS-CoV-2 infections, identifying hotspots and high-risk groups and informing public health responses to the COVID-19 pandemic. We conducted a city-level seroprevalence study in Holyoke, Massachusetts, USA to estimate the seroprevalence of SARS-CoV-2 antibodies and risk factors for seropositivity.

Methods

We invited inhabitants of 2,000 randomly sampled addresses between November 5 and December 31, 2020. Participants completed questionnaires measuring sociodemographic and health characteristics, and COVID-19 exposure history, and provided dried blood spots for measurement of SARS-CoV-2 IgG and IgM antibodies. We calculate total and subgroup seroprevalence estimates based on presence of IgG antibodies using a Bayesian procedure that incorporates uncertainty in antibody test sensitivity and specificity. We account for clustering by household and weighting based on demographic characteristics to ensure estimates represented the city’s population.

Findings

We enrolled 280 households including 472 individuals. 328 underwent antibody testing. The citywide seroprevalence estimate of SARS-CoV-2 IgG was 13.1% (95%CI 6.9-22.3) compared to 9.8% based on publicly reported case counts. Seroprevalence was 16.1% (95%CI 6.2-31.8) among individuals identifying as Hispanic compared to 9.4% (95%CI 4.6-16.4) among those identifying as non-Hispanic white. Seroprevalence was higher among Spanish speaking households (21.9%; 95% CI 8.3-43.9) compared to English speaking households (10.2%; 95% CI 5.2-18.0) and among individuals living in high vulnerability areas (14.4%; 95% CI 7.1-25.5) compared to low vulnerability areas (8.2%; 95% CI 3.1-16.9).

Interpretation

The measured SARS-CoV-2 seroprevalence of IgG antibodies in Holyoke was only 13.1% during the second surge of SARS-CoV-2 in this region, far from accepted thresholds for “herd immunity.” Already vulnerable communities were at highest risk of prior infection. Implementation of local serosurveys in tandem with proactive public health interventions that address disparities in SARS-CoV-2 exposure are crucial to ensure at-risk communities have appropriate educational materials and access to vaccines, testing, and timely treatment.

Funding

The Sullivan Family Foundation, Harvard Data Science Institute Bias 2 program, the US Centers for Disease Control and Prevention.

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  1. ScreenIT

    SciScore for 10.1101/2021.10.13.21264975: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsConsent: Data Collection: The survey tool consisted of an eligibility and informed consent form, one household-level survey, and individual adult and child surveys for each consenting adult and child household member.
    IRB: This protocol was reviewed by the Mass General Brigham Human Research Committee Institutional Review Board (Protocol ID: 2020P002560, November 2nd, 2020).
    Sex as a biological variableNotably, gender is reported as the percent of “Female persons” in Holyoke in the ACS survey results, such that we only have two categories for gender: Female and non-Female, which includes male, transgender, and non-binary persons.
    RandomizationWe then randomly sampled 2,000 addresses from this final list.
    Blindingnot detected.
    Power Analysisnot detected.
    Cell Line AuthenticationAuthentication: DBS sampling has been validated for use in antibody testing of SARS-CoV-2 and other pathogens.

    Table 2: Resources

    Antibodies
    SentencesResources
    9,10 DBS were eluted and tested for the presence of SARS-CoV-2 IgG and IgM receptor-binding domain of the spike protein of SARS-CoV-2 using a quantitative ELISA previously developed and validated using reverse transcriptase polymerase chain reaction (RT-PCR)-positive mild and severe SARS-CoV-2 infections and pre-pandemic samples at Massachusetts General Hospital.11–13 The test specificity and sensitivity estimates were respectively 99.5% (95% CI 99.0-99.8) and 70.6% (95% CI 61.2-79.3%) for IgG antibodies and were calculated using samples from the Boston area.
    IgG
    suggested: None
    Statistical Analysis: Our main SARS-CoV-2 seroprevalence estimate was the proportion of the population that had IgG antibodies detected as this aligns with prior studies.
    had IgG
    suggested: None
    We also calculated seroprevalence estimates with corresponding 95% credible intervals for the following combinations of IgG and IgM antibody positivity: IgG or IgM, IgG only, IgM, and IgM only.
    IgM
    suggested: None
    IgM, IgG only, IgM
    suggested: None
    Individuals from younger age groups and individuals identifying as Hispanic or Latino/Latina were underrepresented in the study population relative to the population of Holyoke. Citywide Seroprevalence of SARS-CoV-2 Antibodies: Of 328 individual samples tested, 27 individuals from 20 households were positive for SARS-CoV-2 IgG or IgM antibodies; after adjusting for clustering, differential response rates and imperfect test sensitivity, this corresponded to a citywide seroprevalence estimate of 13.6% (95%CI: 6.7-23.7).
    SARS-CoV-2 IgG
    suggested: None
    Overall, the prevalence of any anti-SARS-CoV-2 antibodies (measured by IgG or IgM) in this survey corresponds to a cumulative case count of 5,593 compared to the city’s actual case count of 3,963 on January 28th, 2021 based on testing by RT-PCR.
    anti-SARS-CoV-2
    suggested: None
    A high prevalence of SARS-CoV-2 antibodies was also noted among other subgroups such as Spanish-speakers and those with household exposures to COVID-19.
    COVID-19
    suggested: None
    Software and Algorithms
    SentencesResources
    The study team mailed an invitation letter to sampled addresses that contained a QR code and a unique ID for an online survey hosted on REDCap (Research Electronic Data Capture) at Massachusetts General Hospital.
    REDCap
    suggested: (REDCap, RRID:SCR_003445)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

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  2. Version published to 10.1101/2021.10.13.21264975 on medRxiv