The Navy and Marine Corps Public Health Center, in cooperation with the Centers for Disease Control and Prevention (CDC), released findings Tuesday from a joint public health outbreak investigation into how the Covid-19 disease affected crewmembers aboard USS Theodore Roosevelt.

“This is a stealthy virus and the results from this outbreak investigation provides us with increased knowledge about Covid-19 so we can better protect the crew, their shipmates on other vessels, and ultimately the nation,” said Rear Adm. Bruce Gillingham, Navy Surgeon General.

The outbreak investigation included asking volunteers to complete a short survey and provide two specimens for laboratory testing (voluntary blood and nasal swab samples). Antibody testing done on nearly 400 service members of the TR show nearly two thirds (62%) were infected with SARS-CoV-2 and that most were mildly ill. This is the first CDC published report on this specific demographic of young adults.

A total of 382 service members gave blood samples and a subset, 267, provided nasal swab samples. Blood samples were tested for the presence of antibodies, meaning they had been exposed to the virus, and those that were positive were further tested for their ability to prevent infection by neutralizing the virus. Nasal swabs were used to look for virus RNA.

“This study paints a picture of current and prior SARS-CoV-2 infection among young adults living in close quarters,” said study CDC author Dan Payne. “This data will contribute to understanding Covid-19 in the U.S. military, as well as among young adults in other close communal environments.”

In addition to the sample collection, study participants completed a questionnaire that included data on demographics, exposures, protective behaviors service members engaged in, health history, symptoms, and self-reporting of previous Covid-19 test.

Other notable findings include:

  • Nearly two thirds of service members in this sample had reactive antibodies.
  • 44 (18.5%) of service members who were identified as having a current or previous SARS-CoV-2 infection did not report any symptoms.
  • Among those who provided nasal swabs, just over one third tested positive for current infection.
  • Loss of taste or smell was the symptom most associated with current or previous infection; participants reporting these symptoms were 10 times more likely to have infection than were those who did not.
  • Among 12 participants with antibodies that were detected longer than 40 days after symptom onset, eight remained neutralization positive including two participants who were tested 3 months after symptom onset.
  • Among all participants, current or previous infection was more common among males than females, but did not differ significantly by age, race, ethnicity, or history of a preexisting medical condition.
  • Current or previous infection was higher among participants who reported contact with someone known to have Covid-19 (64.2%) compared with those who did not (41.7%) and higher among service members who reported sharing a room with another service member that tested positive (65.6%)  compared with those who did not.
  • Service members who reported taking preventive measures compared to those who did not had a lower infection rate (wearing a face covering (55.8% versus 80.8%), avoiding common areas (53.8% versus 67.5%), and observing social distancing (54.7% versus 70%).

This study is in line with previous outbreaks on cruise ships which reported undetected transmission of Covid-19 due to mild and asymptomatic infection. Like many other respiratory viruses, Covid-19 appears to spread more easily between people in close quarters including those aboard ships and boats. This study shows young, healthy adults with Covid-19 might have mild, atypical, or no symptoms; therefore, symptom-based surveillance might not detect all infections. Use of face coverings and other preventive measures could mitigate transmission in similar settings. The presence of neutralizing antibodies among the majority of participants in this study is promising of at least short-term immunity.

The Navy said it is committed to make the best-informed decisions to protect the health and safety of its sailors. The USS Theodore Roosevelt’s crew has been impacted by this coronavirus harder than any other military unit, and this outbreak investigation provides an opportunity to make a difference and help the nation battle this virus and prevent and contain future outbreaks, the Navy said.