Transmission of SARS-CoV-2 among recruits in a US Army training environment: a brief report

Abstract

Background: In 2020, preventive measures were implemented to mitigate the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among 600-700 recruits arriving weekly at a basic combat training (BCT) facility in the southern United States. Trainees were sorted into companies and platoons (cocoons) at arrival, tested, quarantined for 14 days with daily temperature and respiratory-symptom monitoring and retested before release into larger groups for training where symptomatic testing was conducted. Nonpharmaceutical measures, such as masking, and social distancing, were maintained throughout quarantine and BCT. We assessed for SARS-CoV-2 transmission in the quarantine milieu.

Methods: Nasopharyngeal (NP) swabs were collected at arrival and at the end of quarantine and blood specimens at both timepoints and at the end of BCT. Epidemiological characteristics were analyzed for transmission clusters identified from whole-genome sequencing of NP samples.

Results: Among 1403 trainees enrolled from 25 August to 7 October 2020, epidemiological analysis identified three transmission clusters (n = 20 SARS-CoV-2 genomes) during quarantine, which spanned five different cocoons. However, SARS-CoV-2 incidence decreased from 2.7% during quarantine to 1.5% at the end of BCT; prevalence at arrival was 3.3%.

Conclusions: These findings suggest layered SARS-CoV-2 mitigation measures implemented during quarantine minimized the risk of further transmission in BCT.

Keywords: COVID-19; nonpharmaceutical interventions; public health.

Fig. 1

Flow diagram of SARS-CoV-2 surveillance. After arrival for BCT on Day 0, trainees were enrolled in ES and tested by RT-PCR, both by the training facility and for ES, at T1 and T2, and by serology (for ES only), at T1–T3.

Fig. 2

Prevalence at arrival and incidence of SARS-CoV-2 infection during quarantine among surveillance cohorts, 25 August to 7 October 2020. Trainees were enrolled each week for enhanced SARS-CoV-2 surveillance. Surveillance cohorts were numbered sequentially according to the week of enrollment.

Fig. 3

Timeline of quarantine and laboratory testing events for transmission clusters (Clusters 1–3); the vertical axes indicate cluster members’ sequence ID, and horizontal axes indicate week of enrollment for enhanced surveillance. Cluster 1 members were from Texas, Tennessee, California, Florida, Arkansas and Mississippi, Cluster 2 members were from California, New York and Georgia and Cluster 3 members were from California and Illinois.