Less than 0.01% of San Francisco FD members test positive for COVID-19 antibodies
A UCSF study found that only three out of 1,223 members had antibodies despite nearly half saying they probably or definitely had contact with COVID-19 patients
San Francisco Chronicle
SAN FRANCISCO — Only a handful of San Francisco Fire Department members tested positive for COVID-19 antibodies in a recent UCSF study, even though nearly half of those surveyed said they had probably or definitely been around people infected by the virus.
Just three of 1,223 people who were tested had antibodies for the virus, according to a summary of the results made public by UCSF. The study tested two-thirds of the department’s employees, and featured people in every job category, including firefighters and paramedics.
Researchers believe it is among the first COVID-19 antibody studies of emergency responders who do not work in a hospital, according to UCSF’s Dr. Robert Harrison, who directed the study. Harrison said the low positive tests are likely a reflection of the “powerful public health action” the Bay Area took when it shut down in March, combined with the Fire Department’s pandemic work practices, including the use of N95 respirator masks.
“I was surprised at how low it was,” Harrison said. “However, after I was surprised, I was pleased to see how I think a combination of strong public health leadership (and) sheltering in place combined with both Fire Department management and frontline firefighter adherence to good PPE can work in protecting front line workers.”
Harrison also cautioned that the study team collected its data at the end of June, which would have included some but not all of the rise in COVID-19 cases that the Bay Area has experienced since Memorial Day.
Spokespeople for the Fire Department could not be reached for comment Saturday. But in a virtual town hall with employees Friday, Dr. Jennifer Brokaw, the department’s physician, said employees have adhered well to face covering and surface washing procedures. She expressed optimism that the apparently low infection rates would continue even when the annual influenza season returns this year.
“We’re doing a really good job,” Brokaw said.
Of the study participants, 48% said they had probably come into contact with COVID-19 patients or were certain they had done so. Some of them had only been around someone with the virus once or twice but others had repeated exposure, according to the study summary.
Blood samples from the study were tested at the UCSF Clinical Lab, and any positives were confirmed using additional tests that search for signs of the spike-shaped protein that the virus uses to infect human cells, said Harrison of UCSF. The additional testing ruled out some false positives, and the false negative rate is “extremely small,” he said.
“We can be very confident that the negatives that we have are true negatives,” Harrison said. He also said that antibodies are believed to last at least a few months, so testing in June would pick up cases that date back to March, when the virus’ spread triggered a lockdown.
He also warned that researchers still don’t know if the three people who tested positive for the antibodies are now immune from the virus — or, if they are, how long that immunity will last.
“Nobody, including the positives, should relax and deviate from the existing recommendations for masks and PPE and social distancing and disinfection, all the things that they have in place,” Harrison said.
Other antibody tests among first responders are being conducted in San Jose, Ventura County, New York, Detroit and Rhode Island.
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