“The fact is that a Black person living with H.I.V. in Mississippi is more than six times more likely to die of H.I.V. than a white person in New York — and that’s pretty astonishing, if you think about it,” said James Krellenstein, executive director of the advocacy group PrEP4All Collaboration.

Although “the top line numbers are impressive,” he said, “this does point to a real crisis in the American health care system’s ability to deliver H.I.V. treatment equitably.”

Mr. Krellenstein also sharply criticized the C.D.C. for not closely tracking people’s access to PrEP. Gilead Sciences, which manufactures the only two drugs approved for PrEP, reported an 8 percent drop in use of PrEP in the second quarter of this year, and an uptick of 4 percent in the third.