Mass coronavirus testing in the Marin County city of Bolinas in April revealed no active COVID-19 infections and little to no previous infections among 1,880 residents and first responders, researchers announced Thursday.
Researchers at UCSF, who analyzed tests conducted in April, said the results show the effectiveness of on-site protection – facilitated by the remote coastal enclave miles from any freeway.
“There are very few, if any, people who have been infected in this community, and that’s good news for this community,” says study leader Dr. Bryan Greenhouse, an associate professor in the UCSF department of HIV, infectious disease and global medicine and an investigator at Chan Zuckerberg BioHub. “If there is another wave and they do the same thing again, they can protect themselves from infection.”
In Bolinas, Greenhouse and his colleagues analyzed 1,880 blood samples collected from residents and first responders using both a commercial COVID-19 antibody test produced by Abbott biotech company and an internal version, and combined results from the two tests to statistically estimate population-infection levels .
The result range – between 0 and 3 per 1,000 people – accounted for the fact that tests could present false positives, especially with such a low incidence of cases, Greenhouse said. It is not yet known if the presence of antibodies provides immunity to protect against further infection.
Similar mass testing of Bolinas and Mission District in San Francisco, with both results analyzed by UCSF, reported drastically different results that reveal higher risks depending on how close communities live together and whether they will work under regular shelter.
UCSF reported that diagnostic tests in the Mission District, densely populated with Latinos disproportionately affected by COVID-19, revealed an estimated 2% infection rate among nearly 3,000 people. The rate of infection was much higher – about 6% – among important workers.
UCSF will publish more information at a later date on whether people who participated in the Bolinas study protected at home or went to work.
Bolina’s residents, led by local venture capitalists Jyri Engeström and Cyrus Harmon, raised $ 400,000 and organized a grassroots effort to test everyone in the city in April. The city is a majority white community and has a median income of $ 56,000 below the US average, with 15 percent of residents living below the poverty level. The UCSF study report said local individuals, businesses and agencies provided extra support during the pandemic – including worm and food distribution, rental subsidies and telephone health checks for high-risk residents – to help everyone stay healthy.
“I think we’ve done a really good job of protecting the place and being careful and wearing masks. I’m not surprised by these results, “Dr. Anna O’Malley with the Coastal Health Alliance in Bolinas. “To me, it just underscores the importance of each of us doing our own work to continue to be cautious and support our immune system.”
O’Malley said that West Marin has reported fewer than 10 cases in Bolinas since late April. She is watching closely when companies start to open again in the city and more tourists arrive.
“I still hear and feel within myself caution when it comes to getting involved again,” O’Malley said.
Mallory Moench is a San Francisco Chronicle staff writer. Email: [email protected]