Epidemiologists say the actual number of infections is probably much higher than the official counts. Even with far more widespread testing now than in the early months of the pandemic, they say, many people who have never experienced symptoms may not have been tested or counted.
Ira Longini, a professor of biostatistics at the University of Florida, estimates that about 20 percent of Americans have had the virus – more than twice the number reported. Statistical modeling he recently completed for Florida indicates that one-third of the state’s population was infected at some point, doubling the reported share.
It will be coordinated countrywide study to go beyond model estimates and gain a thorough understanding of how many people actually had the virus, he said. The CDC is doing serological tests, he said, but not enough to give a complete picture.
“The bottom line is that we do not know, but we can guess from modeling,” said Dr. Longini said.
The ratio can vary greatly from place to place. In Dewey County, SD, nearly one in four residents tested positive, but in one in 200 residents in San Juan County, Washington.
Many of the U.S. metropolitan areas with the most reported cases relative to their population are in the south or southwest, where the virus has spread rapidly in recent times, but some are in areas such as the Great Plains that were worse in the fall. The top five are Yuma, Ariz .; Gallup, NM; Bismarck, ND; and Lubbock and Eagle Pass, Texas.
The metro areas with the most new cases per capita over the past two weeks reflect the same trend, and also highlight the ominous nature of the outbreak in California. These areas are Laredo and Eagle Pass, Texas; Domestic Empire, California; Jefferson, Ga .; and Oxnard, California.
It is known that more than a million people have tested positive in Los Angeles County, one of the country’s most important places in the last few months. And George Rutherford, a professor of epidemiology and biostatistics at the University of California, San Francisco, estimated that the actual number of infections there is double, or one in five Angelenos.
“It’s not enough for herd immunity, but it’s enough to dull the curve,” he said.