Severe Acute Respiratory Syndrome Coronavirus 2 Transmission in Intercollegiate Athletics Not Fully Mitigated With Daily Antigen Testing

Abstract

Background: High-frequency, rapid-turnaround severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing continues to be proposed as a way of efficiently identifying and mitigating transmission in congregate settings. However, 2 SARS-CoV-2 outbreaks occurred among intercollegiate university athletic programs during the fall 2020 semester, despite mandatory directly observed daily antigen testing.

Methods: During the fall 2020 semester, athletes and staff in both programs were tested daily using Quidel's Sofia SARS Antigen Fluorescent Immunoassay, with positive antigen results requiring confirmatory testing with real-time reverse-transcription polymerase chain reaction. We used genomic sequencing to investigate transmission dynamics in these 2 outbreaks.

Results: In the first outbreak, 32 confirmed cases occurred within a university athletics program after the index patient attended a meeting while infectious, despite a negative antigen test on the day of the meeting. Among isolates sequenced from that outbreak, 24 (92%) of 26 were closely related, suggesting sustained transmission following an initial introduction event. In the second outbreak, 12 confirmed cases occurred among athletes from 2 university programs that faced each other in an athletic competition, despite receipt of negative antigen test results on the day of the competition. Sequences from both teams were closely related and distinct from viruses circulating in the community for team 1, suggesting transmission during intercollegiate competition in the community for team 2.

Conclusions: These findings suggest that antigen testing alone, even when mandated and directly observed, may not be sufficient as an intervention to prevent SARS-CoV-2 outbreaks in congregate settings, and they highlight the importance of vaccination to prevent SARS-CoV-2 outbreak in congregate settings.

Keywords: SARS-CoV-2; antigen testing; genomic epidemiology.

Figure 1.

Graphic abstract of cryptic transmission that could occur when a person is asymptomatic and the amount of virus remains below the limit of detection (LOD) for antigen tests despite the person’s being potentially infectious to others. This is a schematic and is meant to represent general, not quantitative, relationships among these variables.

Figure 2.

Overview of outbreak 1. A, Epidemic curve for confirmed coronavirus disease 2019 cases (n = 32) among students and staff associated with the athletics program during outbreak 1. Abbreviations: Ag, antigen; Ag−, Ag result negative; Ag+, Ag result positive; RT-PCR, reverse-transcription polymerase chain reaction; RT-PCR+, RT-PCR result positive; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2. B, Graphic representation of known interactions between all persons in the athletics program affected by outbreak 1. Solid black lines represent roommates; red lines, confirmed close contact with a positive case as identified through contact tracing interviews; dashed gray lines, persons who attended indoor team meetings together while following physical distancing policies (>6 ft apart and wearing masks); and red circles, persons who received false-negative antigen results.

Figure 3.

Phylogeny of outbreak 1. A, Time-resolved phylogenetic tree created using Nextstrain tools and nomenclature showing the team sequences contextualized with all available community sequences (gray) for 25 of 32 confirmed cases (78%) associated with outbreak 1; tips affiliated with outbreak 1 are colored red. B, Zoomed-in time-resolved phylogeny showing that all of these samples are part of the same athletics cluster. C, Divergence tree showing the number of mutations each sequence has relative to Wuhan/WH01/2019 (GenBank MN908947.3), a standard reference comparison sequence.

Figure 4.

Overview of outbreak 2. A, Epidemic curve for outbreak 2 showing confirmed coronavirus disease 2019 cases (n = 12) within the 2 intercollegiate teams. Testing was not conducted on day 2. Abbreviations: RT-PCR, reverse-transcription polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 5.

Phylogeny of outbreak 2. A, Time-resolved phylogenetic tree created using Nextstrain tools and nomenclature showing 8 of 12 available samples (67%) from outbreak 2 sequences contextualized with all available community sequences (light gray). Tips affiliated with team 1 are colored red, and team 2’s sequences are colored dark gray. B, Zoomed-in time-resolved phylogeny showing that all of these samples are part of the same athletics cluster. C, Divergence tree showing the number of mutations each sequence has relative to Wuhan/WH01/2019 (GenBank MN908947.3), a standard reference comparison sequence.