SARS-CoV-2 seroprevalence among firefighters in Los Angeles, California

  1. Karen Mulligan
  2. Anders H Berg
  3. Marc Eckstein
  4. Acacia Hori
  5. Anna Rodriguez
  6. Kimia Sobhani
  7. Omar Toubat
  8. Neeraj Sood

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Abstract

We estimate the seroprevalence of SARS-CoV-2 antibodies among a sample of firefighters in the Los Angeles (LA), California fire department in October 2020 and compare demographic and contextual factors for seropositivity.

Methods

We conducted a serological survey of firefighters in LA, California, USA, in October 2020. Individuals were classified as seropositive for SARS-CoV-2 if they tested positive for IgG, IgM or both. We compared demographic and contextual factors for seropositivity.

Results

All firefighters in LA, California, USA were invited to participate in our study, but only roughly 21% participated. Of 713 participants with valid serological data, 8.8% tested positive for SARS-CoV-2 antibodies, and among the 686 with complete survey data 8.9% tested positive for antibodies. Seropositivity was not associated with gender, age or race/ethnicity. Seropositivity was highest among firefighters who reported working in the vicinity of LA International Airport, which had a known outbreak in July 2020.

Conclusions

Seroprevalence among firefighters in our sample was 8.8%, however, we lack a full workplace seroprevalence estimate to compare the relative magnitude against general population seroprevalence (15%). Workplace safety protocols, such as access to personal protective equipment and testing, can mitigate increased risk of infection at work, and may have eliminated differences in disease burden by geography and race/ethnicity in our sample.

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  1. Version published to 10.1136/oemed-2021-107805
  2. ScreenIT

    SciScore for 10.1101/2021.06.03.21258299: (What is this?)

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

    Table 1: Rigor

    EthicsIRB: This study was approved by the Los Angeles (LA) County Department of Public Health Institutional Review Board.
    Consent: Written informed consent was obtained from all study participants.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    SARS-CoV-2-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies were measured using the Abbott Architect instrument (Abbott Laboratories, Chicago, IL.)
    immunoglobulin G ( IgG
    suggested: None
    ) Manufacturer recommended signal-to-cutoff (S/CO) ratios of >1.4 and >1.0 were used as thresholds for seropositivity for IgG and IgM antibodies, respectively.
    IgM
    suggested: None
    Software and Algorithms
    SentencesResources
    SARS-CoV-2-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies were measured using the Abbott Architect instrument (Abbott Laboratories, Chicago, IL.)
    Abbott
    suggested: (Abbott, RRID:SCR_010477)
    Abbott Laboratories
    suggested: None
    All statistical analyses were performed using Stata (StataCorp LLC, College Station, TX).
    StataCorp
    suggested: (Stata, RRID:SCR_012763)

    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: We detected the following sentences addressing limitations in the study:
    This work should be viewed in light of its limitations. Our sample was self-selected, and accounted for approximately 24% of the full LAFD employee population. Participation may have been influenced by prior testing results, household exposure, or worker availability. Nevertheless, our sample demographics were representative of the overall LAFD population. Second, we did not ask respondents questions about their home environment–such as the total number of residents or the size of their home–which could have influenced their exposure to SARS-CoV-2. Furthermore, our sample collection period occurred in the months following the first wave of the pandemic, yet prior to the substantial rise in SARS-CoV-2 cases in LA County and the US beginning in November 2020.[13] Despite this, our study provides seroprevalence estimates and factors associated with SARS-CoV-2 infection for a population that is both at high risk of coming in contact with SARS-CoV-2, but also follows strong workplace protection practices. Between 8.9% and 11.0% of firefighters in LAFD were infected with SARS-CoV-2 depending on whether we adjustment for waning antibodies. We did not observe significant differences in seroprevalence by demographic factors. Furthermore, our results suggest workers in occupations that adhere to similar protection or mitigation workplace protocols are likely to experience similar rates of SARS-CoV-2 infection irrespective of workplace location.

    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

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  3. Version published to 10.1101/2021.06.03.21258299v1 on medRxiv