# Estimating infection prevalence using the positive predictive value of self-administered rapid antigen diagnostic tests: An exploration of SARS-CoV-2 surveillance data in the Netherlands from May 2021 to April 2022

## TL;DR

This study explores using rapid antigen test results to estimate SARS-CoV-2 infection rates in the Netherlands, finding a strong correlation with hospital admissions.

## Contribution

The novel approach uses the positive predictive value of rapid antigen tests to estimate SARS-CoV-2 prevalence in conjunction with RT-PCR confirmation data.

## Key findings

- The positive predictive value of Ag-RDTs was 91.8%, with 88.8% of cases being symptomatic.
- Estimated prevalence ranged between 2–22% in symptomatic and 2–14% in asymptomatic individuals.
- Estimated prevalence correlated with hospital admissions two weeks later (r = 0.68 for symptomatic and r = 0.60 for asymptomatic individuals).

## Abstract

Measuring the severity of the disease of SARS-CoV-2 is complicated by the lack of valid estimations for the prevalence of infection. Self-administered rapid antigen diagnostic tests (Ag-RDTs) were available in the Netherlands since March 2021, requiring confirmation by reverse-transcription polymerase chain reaction (RT-PCR) for positive results. We explored the possibility of utilizing the positive predictive value (PPV) of Ag-RDTs to estimate SARS-CoV-2 prevalence. We used data from all Public Health service testing facilities between 3 May 2021 and 10 April 2022. The PPV was calculated by dividing the number of positive RT-PCR results by the total number of confirmation tests performed, and used to estimate the prevalence and compared with the number of COVID-19 hospital admissions. In total 3,599,894 cases were included. The overall PPV was 91.8% and 88.8% were symptomatic. During our study period, the estimated prevalence ranged between 2–22% in symptomatic individuals and 2–14% in asymptomatic individuals, with a correlation between the estimated prevalence and hospital admissions two weeks later (r = 0.68 (p<0.01) and r = 0.60 (p<0.01) for symptomatic/asymptomatic individuals). The PPV of Ag-RDTs can help estimate changes in SARS-CoV-2 prevalence, especially when used in conjunction with other surveillance systems. However, the used method probably overestimated the true prevalence because of unmonitored differences in test propensity between individuals.