July 23, 2020 -- Between late March and mid-May, it’s probable that up to 10 times more coronavirus infections occurred than the number of cases that were reported during, according to a new study by the CDC’s COVID-19 Response Team.
Published Tuesday in the journal JAMA Internal Medicine, the study looked for antibodies in 10 locations across the U.S. In San Francisco, 1% of samples had antibodies in late April, as compared with nearly 7% in New York City, which was collected in late March.
“It is likely that greater than 10 times more SARS-CoV-2 infections occurred than the number of reported COVID-19 cases; most persons in each site, however, likely had no detectable SARS-CoV-2 antibodies,” the authors wrote.
The research team studied blood samples from more than 16,000 people in 10 locations: San Francisco, Connecticut, south Florida, Louisiana, Minneapolis-St. Paul-St. Cloud, Missouri, New York City, Philadelphia, Utah and western Washington.
The team also estimated that the number of infections ranged from 6 to 24 times the number of reported cases. In Connecticut, for instance, they estimated that 176,000 infections occurred from March through May, which was about 6 times greater than the 29,000 cases reported in early May. In Missouri, the team estimated that 162,000 infections occurred, which was almost 24 times greater than the 7,000 cases reported in late April.
The lower estimate in Connecticut “may reflect increasing availability of testing as the pandemic progressed,” they wrote.
For seven locations — Connecticut, Florida, Louisiana, Missouri, New York City, Utah and Washington state — the research team estimated that more than 10 times the number of infections occurred than reported cases.
Many of the infections likely came from people with COVID-19 who had mild or no symptoms and didn’t take a test or seek medical treatment. They likely contributed to the ongoing spread of the coronavirus while still contagious.
“Because persons often do not know if they are infected with SARS-CoV-2, the public should continue to take steps to help prevent the spread of COVID-19,” the authors wrote.