Fewer than 1 in 10 Americans show evidence of having contracted the coronavirus, a new study of tens of thousands of blood samples has found, underscoring the broad ability the virus still has to spread during cold fall and winter months.
The study, conducted by scientists at the Stanford University School of Medicine, tested plasma from more than 28,500 patients at kidney dialysis centers in July, during the second apex of the pandemic. Their research found that just 9.3 percent of the samples showed evidence of infection by the SARS-CoV-2 virus.
The findings suggest that a huge percentage of Americans are still susceptible to the coronavirus, which has killed more than 200,000 people in the United States already.
It also suggests that millions of coronavirus cases are going undetected. More than 7 million Americans have tested positive for the virus, but the study suggests that fewer than 10 percent of those who get the virus are diagnosed. Even with increased testing capacity, tens of millions of Americans are likely to have contracted the coronavirus without knowing it.
The new research found those living in neighborhoods with higher shares of Black and Hispanic residents were more likely to have contracted the virus than those living in majority-white neighborhoods.
The virus has disproportionately impacted those in big cities and dense urban areas, and minorities are more likely to hold public-facing jobs deemed essential during the pandemic, putting them at increased risk of becoming ill.
Evidence of the coronavirus, known in technical terms as seroprevalence, was highest in Northeastern states that suffered the brunt of the first wave of infections. About 1 in 3 people tested in New York showed signs of previous infection, as did a quarter of those tested in the Northeast. More than 1 in 10 people tested in New Jersey, Maryland, Louisiana, Illinois and the District of Columbia showed evidence of infection too.
Those tested in Western and Southern states were far less likely to show signs of infection. Just 4.2 percent of residents of Western states and 5.1 percent of those in Southern states had been infected by July — though those states were among the hardest hit during the hot summer months.
The study is a stark reminder that the vast majority of Americans are susceptible to the coronavirus as states begin to reopen schools, return to sporting events and congregate indoors as the weather turns chilly.
The number of cases confirmed in the United States every day has already begun rising again, to an average of more than 44,000 new infections each day over the last week. Experts expect a new wave of infections, led by cases in Midwestern and Mountain West states, where the weather turns earlier in the year. Already, states such as Wisconsin and Minnesota are showing alarming increases.
About 29,000 people remain hospitalized with the virus, according to the COVID Tracking Project, an independent group of data scientists. That number is about half the apex of late July, when almost 60,000 people were in treatment, though it has risen in recent days.