When San Francisco implemented its shelter-in-place order in mid-March, the coronavirus continued to spread through the city's Hispanic population in parts of the densely populated Mission District, researchers at the University of California, San Francisco reported Thursday.
For the first six weeks the ordinance was in place, the virus continued to spread among the low-income Latino population in a crowded 16-block area of the district, they found.
The team at UCSF worked with the San Francisco Department of Health, the state of California and community organizers on an initiative offering free Covid-19 tests, both nasal swab tests to diagnose active infections and antibody tests to find past infections. They reached almost 4,000 people in the area between April 25 and April 28.
Most new infections among Hispanic population
The study found that 2% of those given a PCR test -- the most accurate type of diagnostic test -- were infected with Covid-19 at the time of the test. Among those who tested positive, infection rates were almost 20 times higher for Hispanic residents than non-Hispanics and 3.5 times higher among immigrant workers than residents in the district.
Antibody tests indicated 6% of residents had contracted the virus at some point since the beginning of the pandemic, the researchers said in their pre-print report, which has not yet been peer-reviewed.
After comparing the tests, researchers reported, "the vast majority (96%) of new infections were occurring in the Latinx community, whereas those infected earlier in the pandemic were somewhat more representative of the neighborhood as a whole (67% Latinx, 16% White and 17% other)."
Many of those infected could not work from home and could not miss work. Other risk factors for those contracting the virus later, in late April, for example, included frontline service workers, unemployment and a household income of less than $50,000 a year.
"This suggests (the) health effects of ethnic and socioeconomic inequities in the community increased during San Francisco's shelter-in-place ordinance and helps explain why Latinx people have been disproportionately affected by the pandemic," said Dr. Diane Havlir, the chief of the UCSF Division of HIV, Infectious Diseases and Global Medicine and the study's leader.
Determining spread in the community
The survey also found more than half of those testing positive, or 52%, reported no symptoms of Covid-19. Of those, 24% developed symptoms within two weeks of testing, researchers reported. They also noted that those with a positive nasal swab, but negative antibody test, "showed high levels of viral infection regardless of whether they experienced symptoms, suggesting they might continue to be infectious."
Dr. Gabriel Chamie, an associate professor in UCSF's Division of HIV, Infectious Diseases and Global Medicine, said the research reveals how important it is to test both symptomatic and asymptomatic cases to be able to determine how the virus may be spreading in a community.
"Symptom-based testing would have failed to detect over 40% of active infections, and only one person who tested positive required hospitalization, suggesting the vast majority — many of whom had high levels of virus — would not have been diagnosed without community-based testing," Chamie said.
Researchers also detected five different strains of the virus in the community, which was also seen in others parts of the city, after studying the genomic sequence.
This is consistent with multiple independent introductions over time from people either living or working within the study area with subsequent transmission to family members sharing close living quarters," said study co-author Joe DeRisi, a professor of biochemistry and biophysics at UCSF.
The coronavirus testing analysis by UCSF reflects national statistics on Covid-19 and minority populations, which have been disproportionately impacted by the pandemic.
The US Centers for Disease Control and Prevention's National Center for Health Statistics shows almost 17% of Covid-19 deaths were among Latinos while the group makes up just over 18% of the US population.
While the available numbers are grim, they are also incomplete because much of the state and federal data on Covid-19 deaths are preliminary and information on race and ethnicity still isn't available for tens of thousands of cases, CNN reported recently.
Previous research has also shown the virus has adversely impacted the Hispanic population because in so many communities they are considered essential workers.
Additionally, a lack of medical coverage and underlying health conditions, have put the community at risk.