Abstract

Objectives: Estimate the detection limits of the COVID-19 surveillance system (SS) in Chile, by estimating the SARS-CoV-2 true prevalence (TP) and the reported official positivity prevalence (OPP) gap. Study design: Randomized cross-sectional. Methods: Two sampling campaigns (SC) were conducted (October–November 2020 and December 2020–January 2021) in the cities of Temuco, Valdivia, and Osorno. Blood was collected from adults from randomly selected households. Sera were analyzed using a commercial later flow test (LFT). A meta-analysis was performed to estimate LFT-performance in asymptomatic-cases. Data were analyzed using a Bayesian latent class model (BLCM) to estimate TP. Finally, BLCM outputs were compared with the OPP, by calculating the TP/OPP rate. Results: 1124 and 1017 households were visited during the 1st and 2nd SC, respectively. The BLCM rendered TP estimates of 6.5 %, 3.2 %, and 6.6 % for the cities of Temuco, Valdivia, and Osorno, respectively (1stSC), increasing to 9.4 %, 5.0 %, and 7.5 %, 60 days later (2ndSC). Depending on the city and SC, TP/OPP rates varied between 2.3 and 5.7. Conclusion: The national SS was unable to detect 70–79 % of all infected cases, suggesting that mild and asymptomatic cases were scarcely detected. © 2025 The Royal Society for Public Health