The number of coronavirus infections in many parts of the United States is more than 10 times higher than the reported rate, according to data released Friday by the Centers for Disease Control and Prevention.
The CDC study found that in South Florida, just under 2% of the population had been exposed to the virus as of April 10, but the proportion is likely to be higher now given the surge of infections in the state. The prevalence was highest in New York City at nearly 7% as of April 1.
The numbers indicate that even in areas hit hard by the virus, an overwhelming majority of people have not yet been infected, said Scott Hensley, a viral immunologist at the University of Pennsylvania who was not involved in the research.
“Many of us are sitting ducks who are still susceptible to second waves,” he said.
The difference between recorded infections and the actual prevalence in the data was highest in Missouri, where about 2.65% of the population was infected with the virus as of April 26, although many people might not have felt sick. This number is about 24 times the reported rate: nearly 162,000 compared with the 6,800 thought to have been infected by then.
The results confirm what some scientists have warned about for months: that without wider testing, scores of infected people go undetected and circulate the virus.
The CDC researchers tested samples from 11,933 people across six U.S. regions during discrete periods from March 23 through May 3: the Puget Sound region of Washington, where the first COVID-19 case in the country was diagnosed, as well as New York City, South Florida, Missouri, Utah and Connecticut.
The samples were collected at commercial laboratories from people who came in for routine screening, such as cholesterol tests, and were evaluated for the presence of antibodies to the virus — which would indicate previous infection even in the absence of symptoms.
The researchers then estimated the number of infections in each area. New York City, for example, reported 53,803 cases by April 1, but the actual number of infections was 12 times higher, nearly 642,000.
Our Morning Update and Evening Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.