JMIR public health and surveillance 2022

The Importance of Incorporating At-Home Testing into SARS-CoV-2 Point Prevalence Estimates: Findings from a U.S. National Cohort, February 2022.

Qasmieh SA, Robertson MM, Rane MS, Shen Y, Zimba R, Picchio CA, Parcesepe AM, Chang M, Kulkarni SG, Grov C, Nash D
Passive case-based surveillance underestimates the true extent of active infections in the population due to undiagnosed and untested cases, the exclusion of probable cases diagnosed point-of-care rapid antigen tests, and/or the exclusive use of at-home rapid tests which are not reported as part of case-based surveillance. The extent in which COVID-19 surveillance may be underestimating the burden of infection is likely due to time-varying factors such as decreased test-seeking behaviors and increased access to and availability of at-home testing.The objective of this study was to estimate the prevalence of SARS-CoV-2 based on different definitions of a case to ascertain the extent to which cases of SARS-CoV-2 may be underestimated by case-based surveillance.A survey on COVID-19 exposure, infection, and testing was administered to calculate point prevalence of SARS-CoV-2 among a diverse sample of cohort adults between 8-22 February 2022. Three-point prevalence estimates were calculated among the cohort 1) proportion positives based on PCR and/or rapid antigen tests, 2) proportion positive based on testing exclusively with rapid at-home tests, and 3) proportion of probable undiagnosed cases. Test positivity and prevalence differences across booster status were also examined.Among a cohort of 4328, there were a total of 644 cases. The point prevalence estimate based on PCR and/or rapid antigen tests was 5.5% (95% CI: 4.8% - 6.2%), 3.7% (95% CI: 3.1%- 4.2%) based on at-home rapid tests and 5.7% (95% CI: 5.0% - 6.4%) based on the case definition of a probable case. The total point prevalence across all definitions was 14.9% (95% CI: 13.8% - 16.0%). The percent positivity among PCR and/or rapid tests was 50.2%. No statistically significant differences were observed in prevalence between participants with a COVID-19 booster compared to fully vaccinated and non-boosted participants except among exclusive at-home rapid testers.Our findings suggest a substantial proportion of cases were missed by case-based surveillance systems during the Omicron BA.1 surge, when at-home testing was common. Point prevalence surveys may be a rapid tool to be used to understand SARS-CoV-2 prevalence and would be especially important during case surges to measure the scope and spread of active infections in the population.