An assessment of the Chilean COVID-19 surveillance program through the comparison between reported and true SARS-CoV-2 infection prevalence: A case study of three urban centers in southern Chile

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 (1^stSC), increasing to 9.4 %, 5.0 %, and 7.5 %, 60 days later (2^ndSC). 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.