Study investigates an outbreak of SARS-CoV-2 among children and adults after attending an overnight summer camp

In a recent report posted to the medRxiv* preprint server, researchers investigated a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak among individuals who attended an overnight summer camp in Texas in June 2021.

Background

SARS-CoV-2 dispersal dynamics are highly variable, with the majority of COVID-19 patients not transmitting SARS-CoV-2 and only a few coronavirus disease 2019 (COVID-19) patients being responsible for secondary SARS-COV-2 infections. The heterogeneous SARS-CoV-2 transmission indicates that super-spreaders play an essential role in SARS-CoV-2 transmission.

Super-spreader events occur when one infected individual is responsible for a surge in secondary infections. Studies have consistently reported that educational settings do not contribute to SARS-CoV-2 community transmission. On the contrary, the SARS-CoV-2 outbreak in Texas occurred recently among 186 children and adults who attended an overnight summer camp in Texas in June 2021.

The Texas outbreak

The SARS-CoV-2 outbreak occurred among overnight camp attendees in June 2021 at the beginning of the Delta variant wave in the United States (US), while cases were still low in the community but rapidly increasing.

A total of 451 individuals attended the camp, including 364 children (aged below 18 years) and 87 adults (aged above 18 years). After the camp ended, 186 attendees developed reverse transcription-polymerase chain reaction (RT-PCR)-confirmed-SARS-CoV-2 infections.

Among the attendees, 6% and 19% and 6% were partially vaccinated and fully vaccinated, respectively. Pre-arrival RT-PCR test reports were not mandatory for attending the camp, and no post-arrival RT-PCR tests were not performed. A 41% primary attack rate was observed among the camp attendees, of whom 20% and 48% were vaccinated and unvaccinated, respectively.

Ribonucleic acid (RNA) was isolated from 55 nasopharyngeal swabs obtained from SARS-CoV-2-infected camp attendees (n=36) and community members (n=19) and subjected to Oxford Nanopore genome sequencing using the ARTIC approach. Subsequently, libraries were prepared, and bioinformatic analysis was performed. In addition, 4085 complete genomes published in the Global initiative on sharing all influence data (GISAID) database were collected from the Harris County and Galveston County, Texas, and compared phylogenetically to the genomes collected from the camp attendees using the Nextstrain platform.

SARS-CoV-2 amplicons were produced from RNA of all patients, and 70% of the SARS-CoV-2 genome was successfully reconstructed with >10X coverage from 44 samples (13 Galveston County residents and 31 camp attendees). The results aligned with three genomes isolated from Arlington family members who tested SARS-CoV-2-positive on contact with asymptomatic campers after the camp ended.

The evolution of the SARS-CoV-2 genome was determined using the phylogenetic IQ-Tree analysis, which showed that all SARS-CoV-2 genomes obtained from the camp attendees and the Arlington family shared a common ancestor. This was indicative of the initiation of the SARS-CoV-2 outbreak from one SARS-CoV-2-positive camp attendee.

Further, SARS-CoV-2 genomes obtained from the camp attendees who shared risk factors such as common cabins or buses did not demonstrate clustering together. Likewise, SARS-CoV-2 genomes obtained from family siblings did not cluster together, indicating that SARS-CoV-2 transmission occurred during the summer camp. Of interest, several SARS-CoV-2 genomes obtained from individuals who were camp nonattenders clustered together with the camp attendees, indicating that SARS-CoV-2 was transmitted from the camp attendees to the community.

The Nextstrain platform phylogenetic analysis detected 29 genomes that demonstrated clustering with the camp attendees’ genomes obtained after the summer camp ended, i.e., between 28 June 2021 and 30 July 2021. This indicated that SARS-CoV-2 community transmission originated from the camp and continued till July 30, 2021.

Conclusions

Overall, the study findings showed that SARS-CoV-2 super-spreading can occur during large educational gatherings. The Texas outbreak most probably resulted from a single SARS-CoV-2-positive camp attendee who transmitted SARS-CoV-2 to the other campers and subsequently to the community residents. This led to a chain of SARS-CoV-2 transmission which persisted at least till the end of July 2021.

The study highlights the risks of acquiring SARS-CoV-2 infections in overnight summer camps which do not incorporate COVID-19 prevention strategies such as vaccination and SARS-CoV-2 testing before and after the arrival of camp attendees. Further, the authors believe that the present work is the first of its kind to integrate epidemiological, phylogenetic, and genomic approaches for investigating a SARS-CoV-2 outbreak occurring in an overnight summer camp.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.