Aboard an aircraft carrier a respiratory virus is hard to stop: people sleep in shared berths and work in close quarters. In spring 2020 the USS Theodore Roosevelt, deployed to the western Pacific since mid-January, had to stop in Guam at the end of March after COVID-19 spread aboard; about 1,000 service members were found to be infected. In April, the Navy and CDC studied a sample of the crew — and found that the simple precautions still made a difference.
One in five infected service members in the sample had no symptoms. Credit: CDC.
The study
From April 20 to 24, 2020, 382 volunteers — a convenience sample of 27 percent of the 1,417 service members then on the ship or at the base in Guam — answered a questionnaire and gave blood; 267 also gave a nose swab. The blood was tested for antibodies to the virus's spike protein, and positive samples were tested again for neutralizing antibodies, the kind that block the virus. The swabs were tested for the virus itself.
What it found
- Infection was common. 238 of the 382 had evidence of past or current infection; 228 (59.7 percent) had antibodies, and 98 of the 267 swabbed (36.7 percent) had the virus.
- Neutralizing antibodies. Of those with antibodies, 135 (59.2 percent) also had neutralizing antibodies — some more than 40 days after their symptoms began, a promising sign of at least short-term immunity.
- Illness was mostly mild. Nearly 20 percent of infected sailors had no symptoms.
- Loss of taste or smell was the symptom most strongly linked to infection, with 10.3 times the odds; fever, chills and muscle aches followed (odds ratios of 2.8, 2.7 and 2.6). The absence of those symptoms did not rule infection out.
What lowered the risk
| Among sailors who… | Infected, if yes | Infected, if no |
|---|---|---|
| wore a face covering | 55.8% | 80.8% |
| avoided common areas | 53.8% | 67.5% |
| observed social distancing | 54.7% | 70.0% |
Exposure raised it: infection was more common among those who reported contact with a known case (64.2 percent versus 41.7 percent) or who shared a sleeping berth with a crewmate who tested positive (65.6 percent versus 36.4 percent). Men were more likely than women to be infected, which may reflect berthing, separated by sex aboard the ship.
What it means
Young, healthy adults can carry the virus with mild or no symptoms, so screening for symptoms will miss infections in settings like ships, where cruise-ship outbreaks had already shown undetected spread. Face coverings, avoiding common areas and keeping distance lowered the risk even in these conditions.
Limits
The sample was one of convenience, possibly more exposed than the crew as a whole, and everything was self-reported. There were no dates for earlier positive tests, no details on the timing or severity of symptoms, and a single point in time may underestimate the antibody response of those tested early in their infection.
Sources
Based on "SARS-CoV-2 Infections and Serologic Responses from a Sample of U.S. Navy Service Members — USS Theodore Roosevelt, April 2020," by Daniel C. Payne and colleagues from CDC and the U.S. Navy, Morbidity and Mortality Weekly Report (Early Release, June 9, 2020), Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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