About 2% of a sample of more than 1,000 Los Angeles County residents had COVID-19 antibodies in mid-May, according to a new study by the University of Southern California and the L.A. County Department of Public Health.
The results follow those of a serology test conducted in early April in which 4% of the sample population had developed antibodies, indicating there has been little community spread over the last one and a half months as people stayed home, wore masks and practiced physical distancing, officials said. They noted that the difference between the results could be attributed to random variation, different test site locations and efforts to include more Latinos, Asians, and African Americans in the sample population.
The county has confirmed more than 40,000 coronavirus cases and nearly 2,000 deaths since the pandemic began. About 380,000 people have been tested and 9% tested positive.
"We're still far away from heard immunity and need to be conscious of that," said Neeraj Sood, vice dean of the USC Price School of Public Policy.
Medical Services Director Christina Ghaly said the infection rate in L.A. County has fallen below 1, meaning every person with coronavirus is infecting less than one other person.
Ghaly said as the county approaches reopening on July 4, people must continue to protect themselves and others from infection. If the infection rate rises 50% above current levels, 44% of county residents would be infected by December, she said.
"We need to work together to avoid having transmission again increase," she said. "By the time we notice an increased number of cases, there will have been increased spread for a number of weeks ... which could overwhelm our healthcare system."
As in the previous study, men were more likely than women to have been infected, with 2.8% of men testing positive compared to 1.4% of women, Sood said.
Public Health Director Barbara Ferrer said positivity rates differed by income levels rather than race and ethnicity. She said 2.8% of people with a lower income level and 1% of people with a higher income level who were tested were positive.
Although the round of testing conducted May 8, 9, 11 and 12 did not include high-risk groups, Ferrer said Public Health is planning on surveying those living in congregate settings, including skilled nursing facilities, homeless shelters and jails, and people experiencing homelessness. The department is also planning a subsequent survey that will include children.
To date, more than 1,800 people incarcerated in jails, prisons and juvenile detention centers in L.A. County have tested positive for coronavirus. More than 300 people experiencing homelessness have been diagnosed and about half were sheltered.
As of Wednesday, there have been 244 confirmed cases and 14 deaths among Santa Monica residents, with 22 cases reported over the last week. Twenty-four cases were confirmed the week before.
Nearly 170 cases and 24 deaths have been reported at Santa Monica nursing homes.
madeleine@smdp.com
