The number of COVID-19 infections in the community may be “substantially greater” than totals confirmed by authorities, based on SARS-CoV-2 antibody testing among a random sample of adults in Los Angeles County, Calif.
Testing of 863 people on April 10-11 revealed that 35 (4.06%) were positive for SARS-CoV-2–specific antibodies (IgM or IgG), and after adjustment for test sensitivity and specificity, the weighted prevalence for the entire sample was 4.65%,, of the University of Southern California, Los Angeles, and associates .
The estimate of 4.65% “implies that approximately 367,000 adults [in Los Angeles County] had SARS-CoV-2 antibodies, which is substantially greater than the 8,430 cumulative number of confirmed infections in the county on April 10,” they wrote.
It also suggests that fatality rates based on the larger number of infections may be lower than rates based on confirmed cases. “In addition, contact tracing methods to limit the spread of infection will face considerable challenges,” Dr. Sood and associates said.
Test positivity varied by race/ethnicity, sex, and income. The proportion of non-Hispanic blacks with a positive result was 6.94%, compared with 4.42% for non-Hispanic whites, 2.10% for Hispanics, and 3.85% for others. Men were much more likely than women to be positive for SARS-CoV-2: 5.18% vs. 3.31%, the investigators said.
Household income favored the middle ground. Those individuals making less than $50,000 a year had a positivity rate of 5.14% and those with an income of $100,000 or more had a rate of 4.90%, but only 1.58% of those making $50,000-$99,999 tested positive, they reported.
The authors reported numerous sources of nonprofit organization support.
SOURCE: Sood N et al. JAMA 2020 May 18. .