The true number of U.S. coronavirus cases so far could be six to 24 times larger than official figures show, according to CDC data.
The researchers who wrote the analysis say the true burden of disease is likely 10 times greater in most areas than previously understood. But that still means that most Americans haven't been infected. There have been about 3.8 million reported cases in the U.S. so far.
“The findings may reflect the number of persons who had mild or no illness or who did not seek medical care or undergo testing but who still may have contributed to ongoing virus transmission in the population,” said the authors of the study, published Tuesday in JAMA.
Background: The study is based on antibody tests of about 16,000 people conducted between late March and early May in parts of California, Connecticut, Florida, Louisiana, Minnesota, Missouri, New York, Pennsylvania, Utah and Washington state. A positive antibody test means that a person has previously been exposed to the virus.
Limitations: The study authors CDC and state departments of health note that antibody tests can yield false-positive results, but the one used in the study had a 96 percent chance of correctly identifying people with antibodies.
The fact that samples were collected from people seeking health care could also bias the results, the authors said.
“It is possible that specimens were drawn from patients seeking care for suspected COVID-19 symptoms, potentially biasing results, particularly in settings such as NY where disease incidence was higher,” they wrote.
What’s next: Demand for diagnostic testing that detects an active coronavirus infection is still greater than supply, indicating the number of infections is still likely to be undercounted.
Quest Diagnostics, a major testing provider, announced Monday evening it may take up to 14 days to return results for certain patients and average wait times are still more than a week. The company is telling health providers to limit sending in samples from patients that “are likely to be at lower risk.”