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Los Angeles coronavirus infections may be over 40 times higher than reported cases, says study

The results are based on antibody testing. CDC will also start a coronavirus antibody study of up to 325,000 Americans in 25 metros to analyze how Covid-19 is spreading across the US into next year
UPDATED MAY 19, 2020
(Getty Images)
(Getty Images)

Scientists have found that Covid-19 infections in Los Angeles (LA) County greatly exceed the number of confirmed or documented cases. Based on the results of antibody testing, the research team estimates that approximately 4.9% of the county's adult population has antibody to the virus. This estimate implies that approximately 367,000 adults had SARS-CoV-2 (the virus that causes Covid-19) antibodies, which is substantially greater -- 43.5 times higher -- than the 8,430 cumulative number of confirmed infections in the county on April 10, according to the researchers. It includes experts from the University of Southern California, Los Angeles; Sports Medicine Research and Testing Laboratory, Utah; LRW Group, Los Angeles; and Stanford University School of Medicine, Palo Alto, California.

Accordingly, the team says that death rates based on confirmed cases may be higher than rates based on the number of infections. In addition, contact tracing methods to limit the spread of infection will face considerable challenges, they caution. Antibodies are specific proteins made in response to infections. Antibody tests check a person’s blood by looking for antibodies, which show if someone had a previous infection with the virus. A positive test result shows one has antibodies that likely resulted from an infection with SARS-CoV-2. However, these tests have limitations: specificity and sensitivity (true positive rate) vary.

The final analysis in the LA study included 863 adults: 60% were women, 55% were aged 35 to 54 years old. Among the participants, 13% reported fever with cough, 9% fever with shortness of breath, and 6% loss of smell or taste. According to the research team, the results are important as the true extent of Covid-19 infections in the community is not known yet because only people with symptoms have been tested, and the availability of tests has been limited in some places. 

“Inadequate knowledge about the extent of the Covid-19 epidemic challenges public health response and planning. Most reports of confirmed cases rely on polymerase chain reaction-based testing of symptomatic patients. These estimates of confirmed cases miss individuals who have recovered from the infection, with mild or no symptoms, and individuals with symptoms who have not been tested due to limited availability of tests,” say researchers in their findings published in JAMA. “We conducted serologic tests in a community sample to estimate the cumulative incidence of SARS-CoV-2 infection, as serologic tests identify both active and past infections. We used these data to estimate the population prevalence of SARS-CoV-2 antibodies,” they add.

The team, however, says that prevalence estimates could change with new information on the accuracy of test kits used. “Also, the study was limited to one county. Serologic testing in other locations is warranted to track the progress of the epidemic,” say experts. An earlier estimate by the research team had suggested that about 221,000 to 442,000 adults in the LA County may have had the new coronavirus. That estimate was 28 to 55 times higher than the 7,994 confirmed cases of Covid-19 reported to the county by the time of the study in early April. 

Antibody tests check a person’s blood by looking for antibodies, which show if someone had a previous infection with the virus. (Getty Images)

“The estimates also suggest that we might have to recalibrate disease prediction models and rethink public health strategies,” lead investigator Neeraj Sood, a USC professor of public policy at USC Price School for Public Policy and senior fellow at USC Schaeffer Center for Health Policy and Economics, had said when the initial results were released. The study comes even as the US Centers for Disease Control and Prevention (CDC) has decided to launch a major coronavirus antibody study of up to 325,000 Americans in 25 cities. The objective is to track how the new coronavirus is spreading across the US into next year and beyond, CDC spokeswoman Kristen Nordlund and researchers conducting the effort told Reuters. 

Expected to launch in June or July, the CDC study will test samples from blood donors in 25 metropolitan areas for antibodies created when the immune system fights the coronavirus, according to Dr Michael Busch, director of the nonprofit Vitalant Research Institute, who is leading a preliminary version of the research. The initial analysis tested 36,000 samples, and it includes New York, Seattle, the San Francisco Bay Area, Los Angeles, Boston, and Minneapolis. The CDC study will test blood from 1,000 donors in each of the 25 metro areas monthly, for 12 months. Researchers will then test blood from another 25,000 donors at the 18-month mark. 

As of May 19, over 1,508,590 Covid-19 cases have been reported from across the US, and more than 90,350 have died, according to Johns Hopkins.