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CDC study of Roosevelt outbreak finds lower rates of COVID-19 among sailors who wore masks

The Nimitz-class aircraft carrier USS Theodore Roosevelt (CVN 71). (U.S. Navy photo by Mass Communication Specialist 2nd Class Chris Brown/Released)

Preventative measures — such as wearing face coverings, practicing social distancing and avoiding common areas — effectively lowered the COVID-19 infection rate among sailors on the aircraft carrier Theodore Roosevelt, a Navy and Centers for Disease Control and Prevention study said.

Military health officials and the CDC on April 20 began soliciting volunteers from the San Diego-based ship as it was sidelined in Guam battling an outbreak of COVID-19 among its crew.

The Navy said Tuesday a total of 1,273 Roosevelt sailors eventually tested positive for the virus out of a crew of almost 5,000. One, Chief Aviation Ordnanceman Charles Thacker, 41, died of the disease.

Initially the Navy asked 1,400 sailors to participate in the study; 382 did. A Navy Bureau of Medicine and Surgery official said at the time that the demands of the crew to get back to sea might have affected participation rates.

The goal of the study, officials said, was to better understand the behavior of the virus.

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

Because participation in the study was voluntary and self-reporting, it’s possible the results are affected by selection and recall biases, the author notes.

All study participants provided blood samples, which were tested for antibodies which indicate previous exposure to the virus. And 267 participants provided swab samples to test for current presence of the virus.

Sailors also answered survey questions about precautions they took. Those responses, the Navy says, demonstrate the effectiveness of mask-wearing and social distancing.

“Service members who reported taking preventive measures compared to those who did not had a lower infection rate,”the Navy said.

Those wearing a face covering had a 55.8 percent infection rate versus those not wearing masks, who had a 80.8 percent infection rate, the study said.

Sailors who avoided common areas had a 53.8 percent infection rate versus those who didn’t and had a 67.5 percent infection rate.

Those who observed social distancing rules had a 54.7 percent infection rate compared to those who didn’t, who had a 70 percent infection rate, the Navy said in its statement.

Infection rates also were higher among sailors who had close contact with others who had tested positive than among those who had not.

The study also found nearly two-thirds of participants had reactive antibodies to the virus. Of the 60 percent with COVID-19 antibodies, 93 percent had previously tested positive for the virus.

There were some exceptions; 16 sailors with antibodies reported testing negative or were unaware of a positive test result, and 23 sailors who had previously tested positive for the virus had no antibodies in their blood.

The most common symptom of COVID-19 sailors reported is the loss of taste and smell. Sailors reporting those symptoms were 10 times more likely to have an infection than those who did not, the study found.

Navy officials frequently said many sailors from the Roosevelt and the destroyer Kidd, which experienced a similar outbreak, had mild or no symptoms at all.The Roosevelt study found similar results in its survey group — almost 20 percent of those who tested positive reported having no symptoms, while many others had symptoms that were mild or atypical, the study says.

“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,” the Navy statement says. “Use of face coverings and other preventive measures could mitigate transmission in similar settings.”

Mild symptoms also likely contributed to how easily the virus spread on board.

The study found “neutralizing antibodies” in about half those who tested positive for virus antibodies, indicating an immune system response.

“This is a promising indicator of immunity, and in several participants, neutralizing antibodies were still detectable (more than) 40 days after symptom onset,” the study says.

The outbreak on the Roosevelt, which left San Diego for a scheduled deployment in January, marked a low point for the Navy in its fight against COVID-19.

Capt. Brett Crozier, who was captain of the ship when the outbreak began in late March, was removed from command after a letter he sent to Navy captains and Pacific Fleet admirals seeking help to quickly remove the bulk of his crew off the ship in Guam was leaked to the news media.

Then-acting Navy secretary Thomas Modly visited the carrier in April and told the crew Crozier was “too naive or too stupid” for command if he believed his letter wouldn’t be leaked. Modly’s speech also was leaked, and he resigned.

More than 4,000 sailors eventually moved off the ship as others conducted a stem-to-stern deep cleaning. After at least 14 days of quarantine, sailors had to test negative for coronavirus on two subsequent tests before moving back on board.

On Thursday, after more than two months on the sidelines, the Roosevelt resumed normal operations in the western Pacific.


© 2020 The San Diego Union-Tribune