Coronavirus antibodies testing showed little to no infection in Bolinas


Results from April’s Covid-19 antibody test were handed back to Bolinas residents and essentials workers living in West Marin this month. Last week, researchers announced that fewer than six people, and possibly no one, had a history of being infected with the coronavirus at the time of testing. “Our goal with this study was to understand how widely the novel coronavirus had spread in a relatively isolated community like Bolinas before or soon after the stay-home orders went into effect,” study leader Bryan Greenhouse, an infectious disease expert for the University of California, San Francisco, said in a statement. “These antibody results, along with the previously reported P.C.R. data, suggest that few if any people in Bolinas had ever been infected by the virus as of the end of April.” The town-wide testing, which took place over four days at Mesa Park, was spearheaded by wealthy entrepreneurs and supported by community donations and volunteer organizers. The project cost $360,000. The polymerase chain reaction test, which detects active infection using a throat and nasal swab, found no instances of Covid-19 in Bolinas. The antibody tests were performed on 1,880 blood samples, and phlebotomists collected enough blood to perform two tests: A commercial test produced by Abbott Laboratories and an in-house test performed at U.C.S.F. Given the imperfection of available tests, researchers would not give a precise number of positives and cautioned residents against changing their behavior because of their result. The project’s results cannot tell doctors much about the reliability of the tests because there is no way to measure accuracy without a test that is 100 percent reliable. The presence of antibodies is also not yet known to confer immunity from future infection. “There’s a lot we still don’t know about antibody responses to this virus,” Dr. Greenhouse said. The Bolinas testing was followed by the testing of nearly 4,000 residents and workers in the Mission District of San Francisco; there, 83 people tested positive for active infection and 131 tested positive for antibodies. The testing in the city found that socioeconomic inequality fueled transmission: infections in late April were concentrated almost exclusively among low-income Latino people working frontline jobs, according to a U.C.S.F. report.