Genomic Epidemiology of a Severe Acute Respiratory Syndrome Coronavirus 2 Outbreak in a US Major League Soccer Club: Was It Travel Related?

Background Professional soccer athletes are at risk of acquiring severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). United States Major League Soccer (MLS) uses protocol-based SARS-CoV-2 testing for identification of individuals with coronavirus disease 2019. Methods Per MLS protocol, fully vaccinated players underwent SARS-CoV-2 real-time polymerase chain reaction testing weekly; unvaccinated players were tested every other day. Demographic and epidemiologic data were collected from individuals who tested positive, and contact tracing was performed. Whole genome sequencing (WGS) was performed on positive specimens, and phylogenetic analyses were used to identify potential transmission patterns. Results In the fall of 2021, all 30 players from 1 MLS team underwent SARS-CoV-2 testing per protocol; 27 (90%) were vaccinated. One player who had recently traveled to Africa tested positive for SARS-CoV-2; within the following 2 weeks, 10 additional players and 1 staff member tested positive. WGS yielded full genome sequences for 10 samples, including 1 from the traveler. The traveler's sample was Delta sublineage AY.36 and was closely related to a sequence from Africa. Nine samples yielded other Delta sublineages including AY.4 (n = 7), AY.39 (n = 1), and B.1.617.2 (n = 1). The 7 AY.4 sequences clustered together; suggesting a common source of infection. Transmission from a family member visiting from England to an MLS player was identified as the potential index case. The other 2 AY.4 sequences differed from this group by 1-3 nucleotides, as did a partial genome sequence from an additional team member. Conclusions WGS is a useful tool for understanding SARS-CoV-2 transmission dynamics in professional sports teams. A single time-sequentially related cluster of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may be attributable to multiple sources. Whole genome sequencing facilitated the epidemiologic investigation and contact tracing of Major League Soccer players infected with SARS-CoV-2.

Automated summary

MLS used SARS-CoV-2 testing protocol to identify individuals with coronavirus disease 2019. Despite the majority of players being vaccinated, several players still tested positive for SARS-CoV-2, with a family member visiting from England identified as a potential index case. Whole genome sequencing was used to track transmission patterns and identify potential sources of infection.