EpidemiologiCal POpulatioN STudy of SARS-CoV-2 in Lake CounTy, Illinois (CONTACT): Methodology and Baseline Characteristics of a Community-Based Surveillance Study

Introduction: EpidemiologiCal POpulatioN STudy of SARS-CoV-2 in Lake CounTy, Illinois (CONTACT) is an observational, epidemiological study with a 9-month longitudinal follow-up of nonhospitalized persons aged 18 years or older currently living or employed in Lake County, IL. We describe the study design and report baseline characteristics of the study participants, including the proportion of participants with acute or previous SARS-CoV-2 infection at enrollment. Methods: At enrollment and subsequent timepoints, participants recruited through digital and paper-based advertising campaigns reported their occupational and school-based exposure, risk factors, and behaviors, and provided nasal and serum specimens. Stratified enrichment was used to enhance enrollment into medium- and higher-risk groups within four occupational risk groups for SARS-CoV-2 infection. RT-PCR and serologic (IgG) testing were conducted to detect acute or previous SARS-CoV-2 infection in participants, respectively. Results: Between November 2020 and January 2021, 1008 participants (female 70.7%, mean age ± SD 51 ± 13.8 years) completed the questionnaire and diagnostic testing. Among participants, 41.8% (n = 421) were considered low risk, 24.6% (n = 248) were medium-to-low risk, 22.3% (n = 225) were medium-to-high risk, and 11.3% (n = 114) were high risk. Of 56 (5.6%) participants with evidence of acute or previous SARS-CoV-2 infection at baseline, 11 (19.6%) were RT-PCR-positive, 36 (64.3%) were IgG-seropositive, and 9 (16.1%) were positive by both assays. Participants who were adherent vs nonadherent to social distancing measures (odds ratio [95% CI] 0.8 [0.4–1.8]) were less likely, while those in higher vs lower occupational risk groups (2.0 [1.0–4.4]) were more likely to have evidence for acute or previous SARS-CoV-2 infection. Conclusion: In fall/winter 2020/21, 5.6% of adults in a Lake County convenience sample had evidence for acute or previous SARS-CoV-2 infection at baseline. Nonadherence to social distancing measures and high-risk professions were associated with SARS-CoV-2 infection. The study is ongoing and future analyses will assess infection status over time. Clinical Trial Registration: NCT04611230.