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An Outbreak of Covid-19 on an Aircraft Carrier

Our take —

This study of a contained outbreak on a US aircraft carrier in which 1,271 of 4,779 crew members (27%) were infected with SARS-CoV-2, 77% of whom were asymptomatic at the time of diagnosis and 45% of whom never had symptoms. The rapid spread was facilitated by close-quarters conditions and by asymptomatic and pre-symptomatic infected crew members. Though this outbreak provided a unique opportunity to study SARS-CoV-2 epidemiology in a predominantly young, healthy, working-age population, the findings from this military population may not be generalizable to civilians.

Study design

Retrospective Cohort

Study population and setting

Clinical and demographic data, including results of testing by real-time reverse-transcriptase polymerase chain reaction (rRT-PCR), were obtained for all 4,779 crew members on U.S.S. Theodore Roosevelt following a COVID-19 outbreak between March 23 and May 18, 2020, infecting 1,271 persons aboard. All crew members were followed up for a minimum of 10 weeks, regardless of test results or the absence of symptoms.

Summary of Main Findings

SARS-CoV-2 spread quickly among the crew of the U.S.S. Theodore Roosevelt, with transmission facilitated by close-quarters conditions and by asymptomatic and pre-symptomatic infected crew members. 43% of those who tested positive for the virus never had symptoms. Over the course of the outbreak, 1,271 crew members (26.6% of the crew) tested positive for evidence of SARS-CoV-2 infection by rRT-PCR testing, with suspected illness in an additional 60 crew members. Among the crew members with laboratory-confirmed infection, 76.9% (978 of 1271) had no symptoms at the time that they tested positive and 55.0% had symptoms develop at any time during the clinical course. Among the 1,331 crew members with suspected or confirmed Covid-19, 23 (1.7%) were hospitalized, 4 (0.3%) received intensive care, and 1 died.

Study Strengths

The controlled setting allowed for uniform surveillance, treatment, and access to care, and full access to clinical and demographic data for all crew members. Symptom surveillance was rigorous, utilizing both in-person health screenings and self-reporting through a digital symptom checker. All testing was done by rRT-PCR.

Limitations

Data collection from the early days of the outbreak was limited by the quality of records, and may therefore underestimate symptomatic cases, or misestimate onset dates. Observations within a military population, being younger, healthier, and with equal access to healthcare, may not be fully generalizable to civilians.

Value added

The outbreak of Covid-19 on the U.S.S. Theodore Roosevelt provided an unusual opportunity to assess an outbreak in a predominantly young, healthy, working-age population. A majority of infected crew members did not note symptoms at the time of diagnosis, and crew members with unusual or atypical symptoms were less likely to have considered themselves to be infected. This suggests that non-symptomatic or mildly symptomatic crew members played an important role in the rapid spread of the outbreak, much as young adults with asymptomatic infection appear to contribute to spread in civilian populations

This review was posted on: 9 December 2020