Nine out of 10 inmates are male.

There were nearly three-quarters of a million Americans held in local jails in 2018, and about a third of them were black, according to the Bureau of Prison Statistics. In fact, the rate at which black people were jailed was nearly three times the rate at which white people and Hispanics were jailed.

The Cook County Jail in Chicago has emerged as a hot spot for the coronavirus and Covid-19, with more than 300 inmates and more than 200 employees testing positive for the virus. Seventy-three percent of the people in that jail are black and 93 percent are men.

And, to add insult to injury, national data show that 70 percent of the people in local jails are not yet convicted of any crime. Many simply can’t afford to post bail, so they wait in jail on a trial for the charge or until they enter a plea to it.

People living with compromised immune systems are also at risk. H.I.V./AIDS can lead to such a compromised system, particularly among those not in treatments and whose virus hasn’t been suppressed. Black men have the highest rate of new diagnoses of H.I.V.

The H.I.V. prevalence rate for black people is eight times the rate for white people and nearly three times the rate for Hispanics.

There are over a million Americans living with H.I.V. Nearly half a million of those are black. Only 61 percent of those black people received treatment for the virus in 2016 and only about half were able to suppress the virus.

And H.I.V. is now heavily linked to poverty. In 2013, there were 282,100 Medicaid beneficiaries with H.I.V., according to the Kaiser Family Foundation, and they were “more likely to be male (56 percent vs. 42 percent), or black (50 percent vs. 22 percent)” than the Medicaid population overall.