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Half With Recent SARS-CoV-2 in
SF Hispanic District Have No Symptoms
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IAS COVID-19 Conference, July 10-11, 2020
Mark Mascolini
Half of people testing PCR-positive for SARS-CoV-2 in a San Francisco Hispanic neighborhood had no symptoms of COVID-19 [1]. Among these recently infected people, 93% said they could not shelter in place and maintain their income, and 64% had a frontline service job.
Researchers at the University of California, San Francisco (UCSF) noted racial and ethnic disparities emerging from many reviews of COVID-19 rates in the United States. In California, for example, more than 50% of COVID-19 cases occur in Hispanic people, who represent 39% of the state's population. The UCSF team also underlined difficulties in assessing the burden of SARS-CoV-2 infection in different populations and communities because much work focuses on symptomatic people and because testing often remains scarce in heavily affected communities.
To address these issues the researchers planned a mass testing campaign over 4 days in one of San Francisco's Hispanic neighborhoods, the Mission District, which is 58% Hispanic. In cooperation with the Latino Task Force for COVID-19, they advertised the testing campaign door-to-door, aiming to test community residents over 4 years old and people who worked in the community--regardless of symptoms. Testing occurred at outdoor, community-mobilized events. The researchers also collected demographic, socioeconomic, and clinical data.
The testing campaign took place 6 weeks into San Francisco's shelter-in-place phase, on April 25-28, 2020. Over those 4 days, health workers tested 3953 people, 2653 (67%) of them community residents, 460 (12%) workers in the community, and 840 (21%) adjacent-block residents. Similar proportions of tested people were Hispanic (40%) or white (41%), while small proportions were Asian (9%), black (2%), or other races or ethnicities (7%). A small majority of tested people, 53%, were male.
A higher proportion of community workers than residents (6.0% versus 1.7%) tested PCR-positive for SARS-CoV-2. Among community residents, the PCR-positive rate was 20-fold higher in Hispanics than non-Hispanics (3.9% versus 0.2%). The researchers estimated a cumulative infection incidence of 6.1% in residents of the community (95% confidence interval [CI] 4.0 to 8.6).
Comparing 83 people who tested PCR-positive with 3788 who tested PCR-negative, the researchers found that the positive group had a higher proportion of males than females (76% vs 53%, odds ratio [OR] 2.7, 95% CI 1.6 to 4.7, P < 0.001), a higher proportion of Hispanics than non-Hispanics (95% vs 39%, OR 28.3, 95% CI 11.7 to 83.1, P < 0.001), a higher proportion with frontline service jobs (64% vs 27%, OR 6.6, 95% CI 3.9 to 11.6, P < 0.001), a higher proportion of unemployed people (12% vs 6%, OR 5.2, 95% CI 2.2 to 11.3, P < 0.001), a higher proportion with an annual household income below $50,000 yearly than above $100,000 yearly (88% vs 35%, OR 35.4, 95% CI 11 to 216, P < 0.001), and a higher proportion unable to shelter in place and maintain income (93% vs 55%, OR 10.3, 95% CI 4.6 to 29.6, P < 0.001). (All odds ratios are univariate.)
Among the 83 positive PCR tests, 43 (52%) occurred in people with no COVID-19 symptoms at the time of testing. Among PCR-positive, antibody-negative people, viral levels did not differ substantially between asymptomatic and symptomatic individuals. Only 1 PCR-positive person required hospital admission.
The researchers recovered SARS-CoV-2 genomes from 49 of 83 PCR-positive samples (59%). They detected 5 SARS-CoV-2 phylogenetic lineages, a finding suggesting multiple viral introductions to the Mission District from across the city.
The UCSF investigators conclude that during San Francisco's shelter-in-place period, recent SARS-CoV-2 infection in and near this predominantly Hispanic neighborhood "became concentrated almost exclusively" in Hispanic people with low incomes who had service jobs and were unable to work from home. They stress that "symptom-based testing would have missed the majority of infections" in this low-income Hispanic community. Such communities, they propose, need "low-barrier" SARS-CoV-2 testing and economic support programs. Because such a high proportion of recently infected people had no COVID-19 symptoms, the researchers argue that "testing limited to symptomatic people will fail to limit transmission."
Reference
1. Chamie G, et al. High prevalence of asymptomatic SARS-CoV-2 infection found in a Latinx population in San Francisco in a mass testing campaign. IAS COVID-19 Conference, July 10-11, 2020. Track C. https://cattendee.abstractsonline.com/meeting/9307/Session/622
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