Town of Bolinas Antibody Tests Find Minimal History of Infection
UC San Francisco infectious disease scientists have released preliminary results of blood tests for COVID-19 antibodies conducted as part of a community-led project to provide comprehensive COVID-19 testing to residents, essential workers, and first responders in the California town of Bolinas between April 20 and April 24, 2020.
Based on these results, the researchers estimate that at the time of testing, between 0 and 3 in 1,000 people in Bolinas had previously been infected by the SARS-CoV-2 virus that causes COVID-19.
The UCSF team previously reported that all of the nasal and oral swab tests (PCR tests) conducted in the Bolinas community were negative for active infection with SARS-CoV-2 at the time of testing.
The collaboration is the latest example of UCSF’s tightly coordinated work with the state of California and affected communities to respond to the public health crisis presented by COVID-19.
“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. These antibody results, along with the previously reported PCR data, suggest that few if any people in Bolinas had ever been infected by the virus as of the end of April,” said study leader Bryan Greenhouse, MD, an associate professor in the UCSF Division of HIV, Infectious Disease and Global Medicine, based at Zuckerberg San Francisco General Hospital and Trauma Center, and a Chan Zuckerberg Biohub investigator.
Greenhouse and colleagues analyzed 1,880 blood samples collected from Bolinas residents using both a commercial COVID-19 antibody test produced by Abbott and an in-house assay performed at UCSF, and combined results from the two tests to statistically estimate population-level infection rates. Details of the methodology and a more detailed demographic breakdown of the results are currently being prepared for publication and will be publicly shared when available.
The researchers have worked with community partners to return individual antibody test results to Bolinas residents who participated in testing, but emphasize that currently these tests cannot definitively determine whether any given individual has previously been infected with the novel coronavirus, particularly in a setting like Bolinas with extremely low prevalence of COVID-19. Moreover, the presence of antibodies is not yet known to confer immunity to future infection with the disease.
“There’s a lot we still don’t know about antibody responses to this virus,” Greenhouse said. “While the antibody tests we used are amongst the most accurate available, no test is perfect, and individual results should be taken with a grain of salt. We have taken test performance into account to produce our estimate of how many people in the community as a whole were likely to have been previously infected with the virus.”