PLOS Global Public Health · 18 authors, 7 centres
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This community-based household survey in February 2021 estimated the prevalence of active SARS-CoV-2 infection by RT-PCR and past infection by IgG antibodies in three major border cities in Baja California, Mexico, before the national vaccination campaign.
The study used a probabilistic three-stage clustered sampling design to survey 1,126 individuals (aged ≥5 years) in the three most populous cities of Baja California. Testing included RT-PCR on nasopharyngeal swabs and IgG antibody testing on fingerstick blood samples, alongside a questionnaire on COVID-19 knowledge and practices. The weighted overall prevalence of active SARS-CoV-2 infection by RT-PCR was 7.8% (95% CI 5.5–11.0), and IgG seroprevalence was 21.1% (95% CI 17.4–25.2). Ensenada showed higher RT-PCR prevalence than Mexicali and Tijuana. No association was found between border crossing in the past 6 months and infection prevalence (unadjusted OR 0.40, 95%CI 0.12–1.30). Common practices included face mask use and frequent handwashing, but home isolation was uncommon. Limitations include a high refusal rate, potential underestimation of seroprevalence due to the IgG assay used, and restriction to large urban areas.
