Town of Bolinas Antibody Tests Find Minimal History of Infection

By Nicholas Weiler

Two clinicians taking blood from a patient's hand held out of car window
Carlos Medina (foreground), a phlebotomist with Bay Area Phlebotomy and Laboratory Services, is assisted with a patient blood draw by Susanna Lee, a second-year UCSF School of Pharmacy student. Over four days in Bolinas, Calif., researchers collected samples using nasal swabs for diagnostic tests of active COVID-19 infection and finger-prick blood samples for antibody testing. Photo by Barbara Ries

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.”

The results reflect well on California’s early adoption of strict stay-at-home orders and Bolinas’s observation of county and state public health mandates in stopping transmission of the disease, project leaders said.

“During this time, where there’s no coronavirus vaccine and only limited evidence-based treatment, to safely open our society and return to in-person activities, it is critical to gain as much knowledge as possible about transmission and the potential for developing immunity,” said Aenor Sawyer, MD, a UCSF orthopedist and Bolinas resident who served as medical director for the testing program. “This community-wide surveillance project utilizing PCR and antibody testing will hopefully inform policymakers, care providers and community members as to possible transmission patterns of COVID-19, as well as reinforce the importance of public health strategies such as masking, physical distancing, handwashing, and contact tracing.”

“This work has also shed light on the feasibility and importance of more access to reliable testing,” said Sawyer. “There is still much to learn about which antibody tests are most reliable and how to use the antibody information once obtained. This can only be achieved by expanding access to reliable tests and leveraging academic partners to extract meaning from the results.”

The Bolinas community’s ability to follow California’s shelter-in-place ordinances is aided by the town’s remote, rural location in Marin County, miles from any highway, and its commitment to community members in need. Bolinas has a median annual income of $56,000, below the U.S. average. With 15 percent of residents living below the poverty level, local individuals, businesses and agencies have provided additional support during the pandemic – including mask and food distribution, rent subsidies, and phone health-checks for high-risk residents – to help all stay healthy.

The project to provide comprehensive COVID-19 testing in Bolinas began as a community effort to assess and interrupt the local transmission of the disease, and was supported by partnerships with UCSF researchers, county public health officials, local health clinics, a host of volunteers and dedicated participants.

In addition to the efforts cited above, UCSF’s closely coordinated response to COVID-19 with the City and County of San Francisco, other Bay Area communities, and the state of California has included providing forecasting and counseling by UCSF epidemiologists; implementing a statewide contact tracing program in collaboration with the California Department of Health; providing $1 million and clinical expertise for the City to open a COVID-19 unit at Saint Francis Memorial Hospital; and opening a new, 53-bed respiratory isolation unit at UCSF Health’s Mount Zion hospital to expand the city’s overall hospital capacity for potential future surges, while offering dedicated space for current patients.

The proactive effort builds on UCSF’s long-standing commitment to addressing public health crises, which dates back to the University's founding in the mid-19th century, and includes such issues as homelessness, and such diseases as cholera, tuberculosis and HIV/AIDS.

The University of California, San Francisco (UCSF) is exclusively focused on the health sciences and is dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care. UCSF Health, which serves as UCSF’s primary academic medical center, includes top-ranked specialty hospitals and other clinical programs, and has affiliations throughout the Bay Area.