Montgomery County Maryland

 The number of people infected with the coronavirus in different parts of the United States was anywhere from two to 13 times higher than the reported rates for those regions, according to data released Tuesday by the Centers for Disease Control and Prevention.

The findings suggest that large numbers of people who did not have symptoms or did not seek medical care may have kept the virus circulating in their communities. The study is the largest of its kind to date, although some early data was released last month.

“These data continue to show that the number of people who have been infected with the virus that causes Covid-19 far exceeds the number of reported cases,” Dr. Fiona Havers, the C.D.C. researcher who led the study, said in an email. “Many of these people likely had no symptoms or mild illness and may have had no idea that they were infected.”

As demand for coronavirus testing surges around the nation, laboratories that process samples are again experiencing backlogs that have left anxious patients and their doctors waiting days — sometimes a week or more — for results.

At the city and state levels, testing delays could mask persistent rises in case numbers and could cloud ways to combat the coronavirus, as health officials continue to find themselves one step behind the virus’s rapid and often silent spread, experts said.