Last year, over 39,000 people were diagnosed with HIV in the US. That's a tremendous number, but for health officials it's also encouraging; it means that the US has experienced a 19 percent decline in the annual rate of HIV diagnoses over the course of the last decade. Unfortunately, the overall decline in HIV diagnoses also masks some alarming increases among gay men of color.

The CDC identified a 24 percent increase in new HIV diagnoses among gay Latino men between 2005 and 2014, according to data presented by the agency on Sunday at the National HIV Prevention Conference. There was a similar increase for black gay men — about 22 percent — but the number of new diagnoses leveled off after 2010, which may indicate that recent HIV interventions launched by the US government are working. When the data was broken down by age, researchers also saw an 87 percent increase in HIV diagnoses among black and Latino gay men between ages 13 and 24. This increase ended with a 2 percent decline in new diagnoses for young gay black men, however.

Men who have sex with men (MSM) continue to be the group most heavily affected by HIV in the United States. (CDC)

Black women, on the other hand, saw the largest decline in HIV diagnoses of any group. For them, the number of diagnoses was cut almost by half — going down to 4,600 diagnoses in 2014, from 8,000 in 2005.

Because HIV testing rates have been stable for gay Latino men since at least 2005, the CDC thinks that the increase in diagnoses reflect an increase in infections. And that's a problem that the CDC doesn't yet understand, says Eugene McCray, director of the CDC's Division of HIV/AIDS Prevention. "Is it because the prevention interventions are just not getting to that group in a way that's effective?" he asks. "We're going to be looking at that very carefully."

The CDC's announcement shows that although the US is seeing some large improvements, preventative interventions deployed by health officials aren't reaching gay men of color with the same level of success. Right now, there are 1.2 million people in the US who are living with HIV. Health officials hope that new preventatives measures — like the HIV preventative pill — will soon make an important dent in that number.

"We are now equipped with major prevention and treatment advances — so we know what works," McCray says. "Our challenge today is to make sure that everyone is benefitting."