SARS-CoV-2 Seroprevalence Among Firefighters in Los Angeles, California

ObjectiveWe estimate the seroprevalence of SARS-CoV-2 antibodies among firefighters in the Los Angeles, California fire department in October 2020 and compare demographic and contextual factors for seropositivity. MethodsWe conducted a serologic survey of firefighters in Los Angeles, California, USA, in October 2020. Individuals were classified as seropositive for SARS-CoV-2 if they tested positive for immunoglobulin G, immunoglobulin M, or both. We compared demographic and contextual factors for seropositivity. ResultsOf 713 participants, 8.9% tested positive for SARS-CoV-2 antibodies. Seropositivity was not associated with gender, age, or race/ethnicity. Furthermore, firefighters who worked in zip codes with lower income or higher share of minority population did not have higher rates of SARS-CoV-2 infection. Seropositivity was highest among firefighters who reported working in the vicinity of Los Angeles International Airport, which had a known outbreak in July 2020. ConclusionsSeroprevalence among firefighters was no higher than seroprevalence in the general population, suggesting that workplace safety protocols, such as access to PPE and testing, can mitigate increased risk of infection at work. Workplace safety protocols for firefighters also eliminated differences in disease burden by geography and race/ethnicity observed in the general population.

Manufacturer Signal-to-Cutoff Threshold Underestimates Cumulative Incidence of SARS-CoV-2 Infection: Evidence from the Los Angeles Firefighters Study

While SARS-CoV-2 serologic testing is used to measure cumulative incidence of COVID-19, appropriate signal-to-cut off (S/Co) thresholds remain unclear. We demonstrate S/Co thresholds based on known negative samples significantly increases seropositivity and more accurately estimates cumulative incidence of disease compared to manufacturer-based thresholds.