Abstract
Owing to concerns of coronavirus disease 2019 (COVID-19) outbreaks, many congregant settings are forced to close when cases are detected because there are few data on the risk of different markers of transmission within groups. To determine whether symptoms and laboratory results on the first day of COVID-19 diagnosis are associated with development of a case cluster in a congregant setting. This cohort study of trainees with COVID-19 from May 11 through August 24, 2020, was conducted at Joint Base San Antonio-Lackland, the primary site of entry for enlistment in the US Air Force. Symptoms and duration, known contacts, and cycle threshold for trainees diagnosed by reverse transcription-polymerase chain reaction were collected. A cycle threshold value represents the number of nucleic acid amplification cycles that occur before a specimen containing the target material generates a signal greater than the predetermined threshold that defines positivity. Cohorts with 5 or more individuals with COVID-19 infection were defined as clusters. Participants included 10 613 trainees divided into 263 parallel cohorts of 30 to 50 people arriving weekly for 7 weeks of training. All trainees were quarantined for 14 days on arrival. Testing was performed on arrival, on day 14, and anytime during training when indicated. Protective measures included universal masking, physical distancing, and rapid isolation of trainees with COVID-19. Association between days of symptoms, specific symptoms, number of symptoms, or cycle threshold values of individuals diagnosed with COVID-19 via reverse transcription-polymerase chain reaction and subsequent transmission within cohorts. In this cohort study of 10 613 US Air Force basic trainees in 263 cohorts, 403 trainees (3%) received a diagnosis of COVID-19 in 129 cohorts (49%). Among trainees with COVID-19 infection, 318 (79%) were men, and the median (interquartile range [IQR]) age was 20 (19-23) years; 204 (51%) were symptomatic, and 199 (49%) were asymptomatic. Median (IQR) cycle threshold values were lower in symptomatic trainees compared with asymptomatic trainees (21.2 [18.4-27.60] vs 34.8 [29.3-37.4]; P < .001). Cohorts with clusters of individuals with COVID-19 infection were predominantly men (204 cohorts [89%] vs 114 cohorts [64%]; P < .001), had more symptomatic trainees (146 cohorts [64%] vs 53 cohorts [30%]; P < .001), and had more median (IQR) symptoms per patient (3 [2-5] vs 1 [1-2]; P < .001) compared with cohorts without clusters. Within cohorts, subsequent development of clusters of 5 or more individuals with COVID-19 infection compared with those that did not develop clusters was associated with cohorts that had more symptomatic trainees (31 of 58 trainees [53%] vs 43 of 151 trainees [28%]; P = .001) and lower median (IQR) cycle threshold values (22.3 [18.4-27.3] vs 35.3 [26.5-37.8]; P < .001). In this cohort study of US Air Force trainees living in a congregant setting during the COVID-19 pandemic, higher numbers of symptoms and lower cycle threshold values were associated with subsequent development of clusters of individuals with COVID-19 infection. These values may be useful if validated in future studies.
Highlights
Subsequent development of clusters of 5 or more individuals with COVID-19 infection compared with those that did not develop clusters was associated with cohorts that had more symptomatic trainees (31 of 58 trainees [53%] vs 43 of 151 trainees [28%]; P = .001) and lower median (IQR) cycle threshold values (22.3 [18.4-27.3] vs 35.3 [26.5-37.8]; P < .001)
COVID-19 Transmission Among US Air Force Trainees in a Congregate Setting. In this cohort study of US Air Force trainees living in a congregate setting during the COVID-19 pandemic, higher numbers of symptoms and lower cycle threshold values were associated with subsequent development of clusters of individuals with COVID-19 infection
This study was designed to assess symptoms and laboratory values of a young, healthy population living in congregate-setting cohorts, with consistent and extensive use of nonpharmaceutical interventions, who were exposed to individuals with COVID-19 infection, and to assess factors associated with subsequent development of clusters of cases of others with COVID-19 infection within these cohorts
Summary
Coronavirus disease 2019 (COVID-19) is a syndrome caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and associated with outbreaks in congregate settings. Despite its rapid worldwide emergence, there have been reports of effective implementation of nonpharmaceutical interventions, such as physical distancing and rapid isolation of symptomatic patients, that have prevented transmission in both institutions and the general population.4-6Reports characterizing risk factors for COVID-19 spread have suggested that time with infected individuals is a major driver for transmission. In a study evaluating secondary infection in China, more severe disease in the source patient was noted as a risk factor for disease dissemination. Many of these studies have occurred in the setting of no or evolving nonpharmaceutical interventions, which makes it challenging to interpret the contributions of public health measures compared with patients in disease spread.Adding to the uncertainty, the role of asymptomatic transmission in patients with COVID-19 has not been clearly defined. In a study evaluating secondary infection in China, more severe disease in the source patient was noted as a risk factor for disease dissemination.8 Many of these studies have occurred in the setting of no or evolving nonpharmaceutical interventions, which makes it challenging to interpret the contributions of public health measures compared with patients in disease spread. Modeling studies have estimated that to stop spread, there needs to be rapid isolation of symptomatic patients as well as interventions to minimize asymptomatic transmission, such as universal masking and physical distancing.. Modeling studies have estimated that to stop spread, there needs to be rapid isolation of symptomatic patients as well as interventions to minimize asymptomatic transmission, such as universal masking and physical distancing.12 These studies are limited by assumptions but provide the framework for the current COVID-19 response Modeling studies have estimated that to stop spread, there needs to be rapid isolation of symptomatic patients as well as interventions to minimize asymptomatic transmission, such as universal masking and physical distancing. These studies are limited by assumptions but provide the framework for the current COVID-19 response
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