Epidemiologists say the actual number of infections is probably much higher than official counts. Even with tests far more widespread 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, professor of biostatistics at the University of Florida, estimates that about 20% of Americans have had the virus – more than double the number reported. The statistical modeling he completed for Florida recently suggests that a third of the state’s population was infected at some point, four times the reported portion.
National coordination would be needed study to go beyond modeling estimates and have a solid understanding of how many people actually had the virus, he said. The CDC performs some serology tests, he said, but not enough to provide a complete picture.
“The end result is that we don’t know, but we can guess by modeling,” said Longini.
The proportion can vary widely from one place to another. In Dewey County, SD, almost one in four residents tested positive, but in San Juan County, Wash., Only one in 200 did.
Many of the American metropolitan areas with the most reported cases in relation to their populations are in the south or southwest, where the virus has spread rapidly, but some are in areas like the Great Plains, which worsened in the fall. The first five are Yuma, Ariz .; Gallup, NM; Bismarck, ND; and Lubbock and Eagle Pass, Texas.
Metropolitan areas with the highest number of new cases per capita in the past two weeks reflect the same trend, and also highlight the virulence of the outbreak in California. These areas are Laredo and Eagle Pass, Texas; Inland Empire, California; Jefferson, Ga .; and Oxnard, California.
More than a million people are known to have tested positive in Los Angeles County, one of the nation’s top locations in recent months. And George Rutherford, professor of epidemiology and biostatistics at the University of California, San Francisco, estimated that the true number of infections is twice that number, or one in five angelenos.
“It is not enough for the herd’s immunity, but it is enough to smooth the curve,” he said.