A fifth of U.S. prisoners have contracted coronavirus. In some states, it's more than half.

COVID-19 is spreading uncontrolled across the U.S. In prisons, it's at least four times worse.

One in every 20 people in the U.S. has tested positive or COVID-19 over the past nine months, with a total of more than 17 million people infected so far. Meanwhile one in five people incarcerated in America, or more than 275,000 people, have tested positive, data collected by The Marshall Project and The Associated Press reveals — and in states such as Arkansas and South Dakota, that proportion is more than half.

Prisons, where close quarters are standard, are natural hotbeds for COVID-19 — especially those that have allegedly maintained unsanitary conditions and refused to provide masks early on in the pandemic. Also problematic is that in some jails, when "people get sick, not only are they not tested but they don't receive care," Homer Venters, the former chief medical officer at New York's Rikers Island jail complex who now inspects prisons, told The Marshall Project. "So they get much sicker than need be." More than 1,700 incarcerated people have died of the virus.

It's not as if prison coronavirus outbreaks are isolated issues that only affect the people locked up. One in five prison workers have also tested positive; in North Dakota, that number is four in five, The Marshall Project and AP's data show. Those workers bring coronavirus from prisons to the communities outside where they live, and vice versa.

This rampant spread is why some states have decided to prioritize vaccinating prisoners. Other states have said they definitely won't be vaccinating prisoners over other people, and some neglected to even decide when incarcerated people will get the vaccine. Read more from The Marshall Project and The Associated Press here.