COVID-19 outbreak on an American aircraft carrier: A case study in transmission

By Dr. Ananya Mandal, MDNov 16 2020

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – the agent that causes coronavirus disease 2019 (COVID-19) – is a highly infectious pathogen that spreads from human to human in close quarters.

A new study, entitled “An Outbreak of Covid-19 on an Aircraft Carrier”, has published in the New England Journal of Medicine (NEJM), showing the dynamics of infectious spread within close quarters of an aircraft carrier. The study presents a rich case study that may help us better understand the dynamics of SARS-CoV-2’s transmission and thereby fine-tune present policies that aim to prevent its spread. This study was also conducted, say the researchers, to evaluate the epidemiology and outcomes of SARS-CoV-2 infection among “healthy, fit, military-aged adults” confined in close quarters.

The aircraft carrier and COVID-19

The U.S.S. Theodore Roosevelt, a nuclear-powered aircraft carrier with 4,779 personnel on board, was on the western Pacific Ocean when an outbreak of COVID-19 cases occurred. Once the outbreak was detected, the ship was moved to U.S. Naval Base Guam. This base had a 42-bed inpatient facility and could provide essential medical care for U.S. military beneficiaries and others. A joint medical task force joined the support system at the base to aid in the operations.

During the course of the outbreak, all crew members underwent testing and evaluation; their well-being was closely monitored, and they were isolated or quarantined, if necessary.

Study: An Outbreak of Covid-19 on an Aircraft Carrier. Image of American sailors with US flag - USS Theodore Roosevelt docked at the port of Taranto, Puglia, Italy. Image Credit: Massimo Todaro / Shutterstock

Study methodology

For this report, the team collected all clinical and medical data from every crew member on board. This included the results of the testing by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). All the crew members were then followed up for at least ten weeks with or without a positive test or presence of symptoms.

Start of the outbreak

The ship was at sea for 13 days when three of the crew developed symptoms suggestive of COVID-19. They underwent testing with RT-PCR and tested positive. Within 24 hours of this, 400 close contacts of these three and other symptomatic persons were traced.

Four days following the first positive results, the ship docked at the Naval Base Guam, and those who tested positive were evacuated from the base or placed in the base hospital in isolation. Others who had no symptoms of COVID-19 and had one or more negative tests were kept in quarantine either at hotels off base or on Naval Base Guam. Uninfected persons and essential crew members remained on board with the ship docked at port.

Testing and monitoring

For all the crew members in isolation or quarantine, screening for signs and symptoms of the infection was done along with testing. All persons in isolation were checked twice a day for symptoms, temperature and pulse oxygen saturation.

Overall, 4,079 SARS-CoV-2–negative crew members were housed in 11 hotels in Guam in quarantine in single rooms. All persons were asked for a self-assessment of symptoms using a symptom checker developed by Defense Digital Service along with health screenings. These data were gathered each morning and evening at 9 AM and 9 PM, respectively.

Those that showed worsening symptoms were provided adequate hospitalization and care, and all crew members were provided primary care, pharmacy and psychiatric services.

After 14 days, all crew members underwent repeat RT-PCR testing (at the end of the isolation or quarantine period of 14 days). The isolation period ended after a symptom-free three days before exit testing. Those in quarantine with additional symptoms and positive test results were shifted to isolation for at least 14 additional days. All members were followed up for at least ten weeks, even after isolation and quarantine.

The Navy and Marine Corps Public Health Center was responsible for providing data collection and analysis support.

Results

The overall results of the analysis:

• The average age of the crew members was 27 years, with most in general good health that met U.S. Navy standards for sea duty.
• During the outbreak period (between March 23 and May 18, 2020), a total of 1,271 crew members (12.6 percent) tested positive for SARS-CoV-2 by RT-PCR testing
• Most infections occurred within five weeks of the first case detected on board
• 60 crew members did not test positive for COVID-19 but had symptoms similar to the condition meeting the Council of State and Territorial Epidemiologists clinical criteria for COVID-19
• Among those testing positive, 978 of 1,271 (76.9 percent) had no symptoms at diagnosis
• 55 percent (699) of those testing positive developed symptoms during the course of the infection
• A similar spread pattern was seen among men and women on board
• Among 1,331 crew members who had suspected or confirmed COVID-19, 1.7 percent (23) needed hospitalization, 0.3 percent (4) needed intensive care, and one person succumbed to the infection.
• The team wrote, “Although the ship docked in Guam on March 27, 2020, the outbreak continued for at least an additional six weeks”.

Conclusions

The authors of the study concluded that crew members who, when working in closed confines, were still at risk of SARS-CoV-2 infection – despite being young and healthy. Symptoms were absent in over half of those who tested positive facilitating transmission of the virus.

They wrote, “SARS-CoV-2 spread quickly among the crew of the U.S.S. Theodore Roosevelt. Transmission was facilitated by close-quarters conditions and by asymptomatic and presymptomatic infected crew members.”