The US Navy said on Friday it would carry antibody testing of sailors aboard the coronavirus-hit aircraft carrier Theodore Roosevelt to determine whether they were infected by the virus as it spread through the ship.
Sweeping testing on the crew of the USS Theodore Roosevelt aircraft carrier found that two-thirds of sailors who tested positive were asymptomatic, a top military official said.
Nearly the entire crew was tested after the coronavirus outbreak forced the nuclear-powered carrier to dock in Guam. One crew member has died.
The outbreak on the Roosevelt has allowed the Pentagon to document the impact of the coronavirus on a large military population, Joint Chiefs of Staff Vice Chairman General John Hyten told reporters.
"We haven't really tested a whole population and we learn things from the Roosevelt about asymptomatic versus symptomatic," he said.
With so many of the crew symptom-free, it is unclear how many of them had been infected and recovered without anyone realizing they had contracted the virus. Many of these infections could have finished their cycle before testing of the crew began.
The extent of the infections aboard the carrier should become more clear with results of the new "outbreak investigation" the Navy announced that will use serology testing developed by the U.S. Centers for Disease Control and Prevention (CDC).
The serology tests look for the presence of specific antibodies that are created by the immune system's attack response to the presence of the virus and remain in the blood for a period of time.
"We are seeking crew member volunteers," Navy Surgeon General Rear Admiral Bruce Gillingham told reporters.
The roughly thousand volunteers who are sought for testing over the next week or so would also be swabbed for COVID-19, the disease caused by the highly contagious coronavirus, as well as asked to answer a short survey, officials said.
The Navy's testing of the entire 4,800-member crew of the aircraft carrier - which is about 94% complete - was an extraordinary move in a headline-grabbing case that has already led to the firing of the carrier's captain and the resignation of the Navy's top civilian official.
But it has also given scientific researchers a case study about how the virus spreads asymptomatically in a confined environment among mostly younger adults. That cohort has been somewhat underrepresented in the epidemiological data so far.
As of Friday, some 660 sailors - or nearly 14% of the crew - had tested positive for the coronavirus. The Navy said earlier this week that about 60% of those positive tests were among sailors who were symptom-free.
The Navy said medical staff on the island of Guam, where the ship pulled into port, would take the samples and collect questionnaire results. The actual serology tests will be sent to the CDC in Atlanta and analyzed there.
The data could further shed light on how the coronavirus spreads undetected, which could help inform the U.S. national response to the pandemic and efforts to restart the economy.
As of Friday morning, 94 percent of Roosevelt crew had been tested for COVID-19, with 660 positive cases and 3,920 negative.
"It's only 5,000 people, but it is 5,000 people of a certain demographic" that is younger and healthier than the general population, Hyten said.
Studies so far show asymptomatic patients to be between 20 and 50 percent of confirmed cases, according to Hyten, who also serves on the White House coronavirus task force.
"You look at our number. It's almost 60, 70 percent asymptomatic," he said.
Additionally, just over 10 percent of the positive cases had initially come back as negative in late March.
"What we learned is that those negative to positives always transitioned in the 14-day period" of quarantine recommended by health officials worldwide.
"A 14-day quarantine in individual or very small groups, followed by a test, will give us high confidence that we have a clean crew," he said.
The Pentagon, which has stopped all movement of troops around the world, will test almost all of its forces as soon as possible to help decide how to return to normal operations.