Potential Application of SARS-CoV-2 Rapid Antigen Diagnostic Tests for the Detection of Infectious Individuals Attending Mass Gatherings - A Simulation Study

Abstract

Rapid Antigen Diagnostic Tests (RADTs) for the detection of SARS-CoV-2 offer advantages in that they are cheaper and faster than currently used PCR tests but have reduced sensitivity and specificity. One potential application of RADTs is to facilitate gatherings of individuals, through testing of attendees at the point of, or immediately prior to entry at a venue. Understanding the baseline risk in the tested population is of particular importance when evaluating the utility of applying diagnostic tests for screening purposes. We used incidence data from January and from July-August 2021, periods of relatively high and low levels of infection, to estimate the prevalence of infectious individuals in the community at particular time points and simulated mass gatherings by sampling from a series of age cohorts. Nine different illustrative scenarios were simulated, small (n = 100), medium (n = 1,000) and large (n = 10,000) gatherings each with 3 possible age constructs: mostly younger, mostly older or a gathering with equal numbers from each age cohort. For each scenario, we estimated the prevalence of infectious attendees, then simulated the likely number of positive and negative test results, the proportion of cases detected and the corresponding positive and negative predictive values, and the cost per case identified. Our findings suggest that for each reported case on a given day, there are likely to be 13.8 additional infectious individuals also present in the community. Prevalence ranged from 0.26% for "mostly older" events in July-August, to 2.6% for "mostly younger" events in January. For small events (100 attendees) the expected number of infectious attendees ranged from <1 across all age constructs of attendees in July-August, to 2.6 for "mostly younger" events in January. For large events (10,000 attendees) the expected number of infectious attendees ranged from 27 (95% confidence intervals 12 to 45) for mostly older events in July-August, to 267 (95% confidence intervals 134 to 436) infectious attendees for mostly younger attendees in January. Given rapid changes in SARS-CoV-2 incidence over time, we developed an RShiny app to allow users to run updated simulations for specific events.

Keywords: COVID-19; SARS-CoV-2; predictive value; prevalence; rapid antigen test.

Figure 1

Impact of point of detection for each case category on the number of infectious days in the community. Det_CCT = cases are those that are detected at some point during their infectious window, are documented and reported, and are prospectively identified through contact tracing; Det_Symp, cases that are not identified through contact tracing, are detected, documented and reported, and are symptomatic; Det_Asymp, cases that are not identified through contact tracing, are detected, documented and reported, and are asymptomatic; Undet_Symp, individuals that are never officially detected, documented or reported and are symptomatic, these individuals may, or may not restrict their movement; Undet_Asymp, individuals that are never officially detected, documented or reported and are asymptomatic, these individuals do not restrict their movements.

Figure 2

Differences in true and false positives and negatives using two illustrative scenarios of differing prevalences of infectious attendees, and numbers of individuals attending the event.