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Given low testing rates for coronavirus across the country, it can be difficult to gauge from official numbers where outbreaks are actually happening. So researchers at the University of Texas at Austin ran simulations to calculate the risk in each U.S. county that there are sustained, undetected outbreaks — epidemics — already occurring.
They found that even in counties with only one case of COVID-19, there is a 51 percent chance that a growing outbreak is already underway, lending support to the idea that people should distance themselves from others even if their area only has a small number of reported cases. The research means most people in the United States — and in Maine — are likely living in communities where the virus is already spreading widely.
There are only two counties in Maine — Cumberland and York — where the Maine Center for Disease Control and Prevention has officially confirmed community transmission and where the researchers said there was a 100 percent probability of an epidemic. Maine defines community transmission as happening when there are at least 10 confirmed cases, and 25 percent are not connected to other known cases or travel.
However, “In any outbreak situation, we are only seeing a fraction of the cases that are out there,” Nirav Shah, director of the Maine CDC, has said. “What we know from other outbreaks is that there are almost certainly cases around you.”
Largely because people who have mild symptoms or none at all can pass the disease to others, the odds are high that local communities already have epidemics. There is a 98 percent chance of an epidemic occurring both in Penobscot and Kennebec counties, according to the study published April 3. (At the time of the study, Penobscot had 16 confirmed cases, and Kennebec had 19. Penobscot now has 31 cases, and Kennebec has 26.)
The study defines an epidemic as an outbreak that continues exponentially, ultimately infecting a large portion of a population, instead of dying out on its own.
There is a 96 percent chance of an epidemic in Androscoggin County, a 95 percent chance in Sagadahoc County, a 93 percent chance in both Lincoln and Oxford counties, and a 91 percent chance in Knox County.
There’s a 79 percent chance of an epidemic in Franklin County, and a 70 percent chance in Somerset, Hancock and Waldo counties.
The study calculated a 9 percent chance of an epidemic in Aroostook, Piscataquis and Washington counties, but that was before Aroostook reported two cases and Washington reported one. Piscataquis still has not recorded any confirmed cases.
The study assumes that one in 10 COVID-19 cases are tested and reported. It obtained county-level estimates for COVID-19 cases from a New York Times data repository.
It created a map to simulate the likelihood of outbreaks in each county, using the color red to show where COVID-19 is likely spreading.
“It is likely that our entire map will be bright red within a week or two, given that COVID-19 spreads very quickly and often silently,” the authors, Emily Javan, Dr. Spencer J. Fox and Dr. Lauren Ancel Meyers, wrote, emphasizing how the fate of outbreaks hinges on the speed of local interventions.
“Early and extensive social distancing can block community transmission, avert rises in hospitalizations that overwhelm local capacity, and save lives,” they wrote.
Watch: Why the Maine CDC breaks down coronavirus cases by county, not town