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 analysis is part of a wide-ranging set of surveys started by the CDC 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 CDC study found, for instance, 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.
“This study underscores that there are probably a lot of people infected without knowing it, likely because they have mild or asymptomatic infection,” said Dr. Fiona Havers, who led the CDC study. “But those people could still spread it to others.”
She emphasized the importance of hand-washing, wearing cloth masks and social distancing to stop the spread of the virus from people without symptoms.
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.