Serological surveys to estimate cumulative incidence of SARS-CoV-2 infection in adults (Sero-MAss study), Massachusetts, July–August 2020: a mail-based cross-sectional study
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Abstract
To estimate the seroprevalence of anti-SARS-CoV-2 IgG and IgM among Massachusetts residents and to better understand asymptomatic SARS-CoV-2 transmission during the summer of 2020.
Design
Mail-based cross-sectional survey.
Setting
Massachusetts, USA.
Participants
Primary sampling group: sample of undergraduate students at the University of Massachusetts, Amherst (n=548) and a member of their household (n=231).
Secondary sampling group: sample of graduate students, faculty, librarians and staff (n=214) and one member of their household (n=78). All participants were residents of Massachusetts without prior COVID-19 diagnosis.
Primary and secondary outcome measures
Prevalence of SARS-CoV-2 seropositivity. Association of seroprevalence with variables including age, gender, race, geographic region, occupation and symptoms.
Results
Approximately 27 000 persons were invited via email to assess eligibility. 1001 households were mailed dried blood spot sample kits, 762 returned blood samples for analysis. In the primary sample group, 36 individuals (4.6%) had IgG antibodies detected for an estimated weighted prevalence in this population of 5.3% (95% CI: 3.5 to 8.0). In the secondary sampling group, 10 participants (3.4%) had IgG antibodies detected for an estimated adjusted prevalence of 4.0% (95% CI: 2.2 to 7.4). No samples were IgM positive. No association was found in either group between seropositivity and self-reported work duties or customer-facing hours. In the primary sampling group, self-reported febrile illness since February 2020, male sex and minority race (Black or American Indian/Alaskan Native) were associated with seropositivity. No factors except geographic regions within the state were associated with evidence of prior SARS-CoV-2 infection in the secondary sampling group.
Conclusions
This study fills a critical gap in estimating the levels of subclinical and asymptomatic infection. Estimates can be used to calibrate models estimating levels of population immunity over time, and these data are critical for informing public health interventions and policy.
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SciScore for 10.1101/2021.03.05.21249174: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement Consent: The email provided information about the study and links to a screening eligibility survey, informed consent document, initial survey regarding COVID-19 risk factors, and information regarding shipping addresses. Randomization A total of 1,001 individuals were then randomly selected to receive a sampling kit. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Cell Line Authentication not detected. Table 2: Resources
Antibodies Sentences Resources Samples were then assayed for SARS-CoV-2 antibodies according to published protocols. SARS-CoV-2suggested: NoneBatches were control for purity by SDS-PAGE followed by Coomassie … SciScore for 10.1101/2021.03.05.21249174: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement Consent: The email provided information about the study and links to a screening eligibility survey, informed consent document, initial survey regarding COVID-19 risk factors, and information regarding shipping addresses. Randomization A total of 1,001 individuals were then randomly selected to receive a sampling kit. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Cell Line Authentication not detected. Table 2: Resources
Antibodies Sentences Resources Samples were then assayed for SARS-CoV-2 antibodies according to published protocols. SARS-CoV-2suggested: NoneBatches were control for purity by SDS-PAGE followed by Coomassie staining and ELISA using an anti His-tag monoclonal antibody. anti His-tagsuggested: NoneSamples were tested against IgG and positive samples were confirmed and tested with anti IgM antibodies. anti IgMsuggested: NoneExperimental Models: Cell Lines Sentences Resources 18,19 The RBD protein was produced in-house via transfection of HEK293T cells using polyethylenimine (Plasmid was a generous gift from Pr. F. Kramer mount Sinai School of Medicine). HEK293Tsuggested: NCBI_Iran Cat# C498, RRID:CVCL_0063)Software and Algorithms Sentences Resources All survey responses were collected and stored in REDCap. REDCapsuggested: (REDCap, RRID:SCR_003445)Results from OddPub: Thank you for sharing your data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:These results reinforce results from other studies: asymptomatic illness is an important contributor to observed force of infection; and important limitations of testing availability at the time of survey. Differing antibody dynamics have been reported in other studies. A number of studies have found sustained antibody levels for over 3 months,29,30 while others have found IgG levels can remain 6 months or more.31–33 An additional study has reported rapid waning of routine serological markers in individuals who had lower initial antibody responses.34. Only 7.1% of those with high titers at baseline seroreverted to a level below the threshold for positivity within 60 days, compared to 64.9% of those with lower titers at baseline.34 Evidence for IgM seropositivity was not detected in any of IgG positive samples, which is consistent with results from other surveys studies that included asymptomatic or subclinical populations due to rapidly waning titers.32,35 Studies have shown that IgM levels decline more rapidly after infection than IgA and IgG levels, 30,36,37, and this is especially apparent with asymptomatic and sub-clinical infections.32,35 Trends in the patterns of SARS-CoV-2 antibody levels vary greatly depending on the timing of sampling and severity of disease.31,32,35 Seroconversion times vary depending on the study, but one study found a median time-to-seroconversion for IgM of 8 days and median seroconversion for IgG of 10 days. Additionally, the SARS-CoV-2 IgG resp...
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.
- No funding statement was detected.
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