SARS-CoV-2 transmission in intercollegiate athletics not fully mitigated with daily antigen testing

Abstract

Background: High frequency, rapid turnaround SARS-CoV-2 testing continues to be proposed as a way of efficiently identifying and mitigating transmission in congregate settings. However, two 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 (FIA), with positive antigen results requiring confirmatory testing with real-time reverse transcription polymerase chain reaction (RT-PCR). We used genomic sequencing to investigate transmission dynamics in these two outbreaks.

Results: In Outbreak 1, 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 Outbreak 1, 24 (92%) of 26 were closely related, suggesting sustained transmission following an initial introduction event. In Outbreak 2, 12 confirmed cases occurred among athletes from two university programs that faced each other in an athletic competition despite receiving negative antigen test results on the day of the competition. Sequences from both teams were closely related and unique from strains circulating in the community, suggesting transmission during intercollegiate competition.

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 highlights the importance of supplementing serial antigen testing with appropriate mitigation strategies to prevent SARS-CoV-2 outbreak in congregate settings.

Summary: High frequency, rapid turnaround SARS-CoV-2 testing continues to be proposed as a way of efficiently identifying and mitigating transmission in congregate settings. However, here we describe two SARS-CoV-2 outbreaks occurred among intercollegiate university athletic programs during the fall 2020 semester.

Figure 1.

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

Figure 2.. Overview of Outbreak 1

A) Epidemic curve for confirmed COVID-19 cases (n = 32) among students and staff associated with the athletics program during Outbreak 1. Abbreviations: Ag = antigen; COVID-19 = coronavirus disease 2019; RT-PCR = reverse transcription–polymerase chain reaction. B) Graphical representation of known interactions between all persons in the athletics program affected by Outbreak 1. Roommates are shown by a solid black line; confirmed close contact with a positive case as identified through contact tracing interviews is shown with a red line; r persons who attended indoor team meetings together while following physical distancing policies (> 6 feet apart and wearing masks) are shown with a dashed gray line; persons who received false negative antigen results are shown with a red circle.

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 (78%) of 32 confirmed cases associated with Outbreak 1; tips affiliated with Outbreak 1 are colored red. B) Zoomed in time-resolved phylogeny showing 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 (n = 12) COVID-19 cases within the two intercollegiate teams. Testing was not conducted on day-2.

Figure 5.. Phylogeny of Outbreak 2.

A) Time-resolved phylogenetic tree created using Nextstrain tools and nomenclature showing 8 (67%) of 12 available samples 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 all 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.