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The impact of population-wide rapid antigen testing on SARS-CoV-2 prevalence in Slovakia

Our take —

This study reports the results of a national rapid antigen testing campaign in Slovakia, which was associated with a greater than 50% reduction in estimated SARS-CoV-2 prevalence over a one week period. Results should be interpreted cautiously, as mass testing occurred in the context of many other SARS-CoV-2 control measures.

Study design

Ecological, Modeling/Simulation

Study population and setting

Between October 23 and November 8, 2020, The Slovak Ministry of Health implemented SARS-CoV-2 testing nationally using rapid viral antigen tests in three phases: (1) a pilot phase (October 23-25) in four high-incidence counties; (2) a mass testing campaign implemented nationally in 79 counties (October 31-November 1; round 1); and (3) follow-up testing one week later in 45 counties with the highest SARS-CoV-2 prevalence (November 7-8; round 2). Residents were instructed to present to central testing hubs in their jurisdictions, staffed with over 60,000 trained employees nationally, during each testing campaign phase. Testing was performed using the SD-Biosensor Standard Q rapid antigen test on nasopharyngeal swabs. A national lockdown was imposed in Slovakia at the time of mass testing campaigns, which included business and school closures (for students ages 10 years and above): residents were instructed to stay at home and leave only for essential purposes (i.e., travel to/from work, accompanying children to school, seeking medical care). After estimating changes in SARS-CoV-2 prevalence (defined as the proportion of SARS-CoV-2 tests performed during a campaign phase with positive results) between mass testing campaigns, the authors used an epidemic microsimulation model to evaluate whether observed changes in SARS-CoV-2 prevalence could be attributed to scale-up of rapid antigen testing.

Summary of Main Findings

Nearly 5.3 million rapid antigen tests were conducted across the three testing phases, detecting 50,466 positive cases overall. Population coverage of antigen tests during the pilot, round 1, and round 2 phases was 65%, 66%, and 62%, respectively (84-87% of the census age-eligible population). Test positivity in the pilot phase was 3.91%, 1.01% during round 1, and 0.62% in round 2. Specificity of the rapid test was estimated to be 99.85%. In the 45 counties included in rounds 1 and 2, the estimated SARS-CoV-2 prevalence decreased by 58% (95% CI: 56–63%) between campaigns, with substantial heterogeneity observed between counties. In the four counties included in the pilot phase, infection prevalence decreased by 82% (95%CI: 81-83%) between the pilot and round 2. In microsimulation models, the authors assumed varying levels of effectiveness of other SARS-CoV-2 control measures which were implemented at the same time as testing (e.g., lockdowns, school closures): the only scenario that sufficiently reproduced observed reductions in SARS-CoV-2 prevalence between testing campaigns was a scenario in which confirmed COVID-19 cases isolated from household contacts, suggesting that declines in SARS-CoV-2 prevalence were unlikely to have occurred in the absence of the mass testing campaign.

Study Strengths

This study analyzes an impressive amount of SARS-CoV-2 rapid antigen testing data from three testing campaigns, including one conducted at a national scale in Slovakia.

Limitations

Participation in viral antigen testing was voluntary and required travel to testing sites; the estimated SARS-CoV-2 prevalence, therefore, may not accurately reflect true SARS-CoV-2 transmission dynamics in the population. Despite using an epidemic simulation model to estimate the potential impact of mass testing on SARS-CoV-2 transmission, declines in SARS-CoV-2 prevalence may not be attributable to scale-up of viral antigen tests. Mass testing campaigns were also conducted in the context of a national lockdown, where residents were instructed to only leave their homes for essential purposes. No empirical data were presented on isolation or quarantine of infected cases and their contacts, respectively, which is essential to concluding whether observed reductions in cases were attributable to mass testing or other interventions. While the test used was a rapid antigen test, it was conducted by tens of thousands of trained professionals using nasopharyngeal swabs; thus, results may not be generalizable to most other settings.

Value added

This is among the first studies to assess the impact of mass rapid viral antigen testing on SARS-CoV-2 transmission dynamics.

This review was posted on: 1 May 2021