Actual Coronavirus Infections Vastly Undercounted, C.D.C. Data Shows

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 on Friday by the Centers for Disease Control and Prevention.

The analysis is part of a wide-ranging set of surveys started by the C.D.C. to estimate how widely the virus has spread. Similar studies, sponsored by universities, national governments and the World Health Organization, are continuing all over the world.

The C.D.C. study found, for instance, that in South Florida, just under 2 percent 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 percent 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.