Less than 1% of Hawaii health care workers tested for COVID-19 antibodies were found to have been exposed to the virus.

Nineteen employees of Hawaii Pacific Health — parent company of Kapiolani Medical Center for Women & Children, Pali Momi Medical Center, Straub Medical Center and Wilcox Health on Kauai — tested positive for the coronavirus antibodies. They were among 3,296 who voluntarily participated in the state’s first antibody screenings to determine the level of COVID-19 infection in the health care workforce.

The 0.58% positive rate among those tested as of Friday is lower than expected since front-line workers have greater exposure to COVID-19 than the average person, said Dr. Melinda Ashton, HPH executive vice president and chief quality officer. An additional 275 workers from companies that requested antibody testing as part of the program were all negative, she said.

“We think most of these antibody results is probably from exposure while there was more virus in the community. The vast majority of our employees that have been tested have not had any contact with this virus. It also tells us our approaches to personal protective equipment have been successful,” she said. “There are a lot of people who were tested who were very disappointed they don’t have the antibody. We don’t want people to have that false assurance, so a low rate of positivity leaves a lot more people knowing they’re not protected.”

The state Department of Health is contacting the antibody-positive employees to have them tested for active infection, said spokeswoman Janice Okubo. If any test positive, they will have to quarantine for at least 14 days.

The first laboratory-based antibody tests were done through Clinical Labs of Hawaii to detect immunoglobulin G, or IgG, which develops about two weeks after COVID-19 infection. Diagnostic Laboratory Services Inc. has also started coronavirus antibody testing, with two of 134 testing positive as of Thursday.

With similar viruses, the presence of antibodies — proteins produced by the immune system in response to infections — generally means a person has immunity. However, the Centers for Disease Control and Prevention has said it does not know if COVID-19 antibodies will protect against future infections.

Hawaii’s tally of coronavirus cases rose by one case, reported on the Big Island, on Friday for a total of 638. There were 56 active infections and 565 patients now classified as “released from isolation” since the start of the outbreak — more than 90% of those infected. The state’s coronavirus death toll remained at 17.

Of the more than 38,995 coronavirus tests for active infection by state and private laboratories, just 1.6% have been positive.

The antibody tests shows the “current number of people we’ve identified as having COVID-19 in the community is probably really accurate,” Ashton said. “We probably haven’t missed a big group of people who would’ve been positive if only we had tested them. I feel very comfortable that we’re ready to open up the kama’aina economy. We could safely do away with the interisland restrictions. I think there’s lots of questions about what the impact would be as we open up to visitors of other places, but I think we’re in a much better situation now than when the virus first hit.”

The tests, authorized by the U.S. Food and Drug Administration for emergency use during the public health crisis, are manufactured by Abbott, the same firm that developed a 15-minute COVID-19 rapid test under investigation for accuracy by the Food and Drug Administration.

Another 2,000 Hawaii Pacific Health workers are planning to get tested, Ashton said, adding that the Abbott antibody tests have proved to be among the most accurate in the nation.

“This really low level (of positive antibody tests) is useful information for everybody. I also think it’s been reassuring to our employees … just to get an answer (of whether or not they’ve been infected). We’re all waiting to see what happens next. There’s no plans to test again at this point. It depends on what the future holds.”