While the national annual HIV infection rate dropped by an estimated 15 percent between 2008 and 2015, a few key subgroups saw a rise in yearly new HIV infections, also known as HIV incidence. During this period, HIV incidence among 25- to 34-year-old men who have sex with men (MSM) increased by an estimated 45 percent while the rate increased 25 percent among Latino MSM.

These figures come from the Centers for Disease Control and Prevention’s (CDC) new, in-depth analysis of epidemic trends in the United States. Published in the Annals of Internal Medicine, the report is a more precise and granular version of reports on epidemic trends that CDC officials presented at the 2017 Conference on Retroviruses and Opportunistic Infections (CROI) in Seattle a year ago.

At that time, the agency estimated that HIV incidence declined 18 percent between 2008 and 2014. This new estimate, therefore, represents a disappointing reduction in that hopeful figure.

Prior to 2008, HIV incidence was essentially stable in the United States for the decade following the beginning of the modern era of combination antiretroviral (ARV) treatment.

The CDC has stated that the declining overall HIV rate seen in recent years is likely driven by a rising rate of full suppression of the virus among those living with HIV in the United States. The risk of transmission by people with HIV who maintain an undetectable viral load thanks to ARV treatment is effectively zero, according to the cumulative findings of multiple large studies. The CDC recently estimated that about half of those living with the virus had a fully suppressed viral load in 2014, and epidemic trends suggest that the figure has likely risen in the years since.

For their new report, CDC researchers relied on data from the National HIV Surveillance System (NHSS), looking at new diagnoses and the first CD4 test result following diagnosis among individuals age 13 and older. They fed that data into a mathematical model that estimated the time of each infection to develop estimates regarding how many people in various subgroups contracted the virus annually.

Note: All figures quoted from the report regarding HIV prevalence (the number of people living with the virus), HIV incidence and the proportion of the HIV population that is undiagnosed are estimates.

Between 2008 and 2015, the number of people who contracted HIV annually in the United States declined 14.8 percent, from 45,200 to 38,500.

During this period, HIV incidence attributable to heterosexual contact declined 6.3 percent annually, from 13,000 to 8,800; additionally, the rate declined 10.7 percent annually among people who inject drugs (PWID), from 3,800 to 2,200 and 4.3 percent among MSM who inject drugs, from 1,500 to 1,200.

The decline in HIV incidence seen among PWID seems to be leveling off, given the fact that the rate remained stable in 2014 and 2015. This could be a sign that the opioid crisis stands poised to reverse some of the hard-fought gains, such as access to syringe exchange services, that have driven down incidence among this population since the early 2000s.

HIV incidence among MSM remained essentially stable: 26,700 members of this population contracted the virus in 2008 compared with 26,200 in 2015. During this time HIV, incidence among those 13 to 24 years old declined 3 percent per year, from 9,800 to 7,700 transmissions; rose 5.7 percent per year among those 25 to 34 years old, from 6,900 to 10,000 (a 44.9 percent increase overall); declined 4.7 percent per year among those 35 to 44 years old; remained essentially unchanged among those 45 to 44 years old, at a respective 3,300 and 3,000; and rose 4.1 percent per year among those age 55 and older, from 1,000 to 1,300 (a 30 percent increase overall).

Among MSM, HIV incidence broken down by ethnicity saw essentially no change between 2008 and 2015 in the rate among African Americans, from 9,900 to 9,800 transmissions; a 3.1 percent rise per year among Latinos, from 6,300 to 7,900 (a 25.4 percent increase overall); and essentially no change among Asians, at a respective 530 and 490.

MSM make up an estimated 2 percent of the U.S. population and accounted for 67 percent of all those diagnosed with HIV in 2015. Consequently, they had the highest rate of annual HIV infections per 100,000 people among all risk groups, at 514 transmissions, a rate 16 times greater than that of PWID (32 transmissions per 100,000) and 135 times that of heterosexuals (3.8 transmissions per 100,000).

HIV prevalence increased 14.7 percent during the study period, rising from 956,200 U.S. residents living with the virus in 2008 to 1,122,900 in 2015. This increase is cause for some celebration, as it is in part the result of effective ARV treatment allowing people with the virus to live longer.

Prevalence was highest among MSM, among whom the number of people living with HIV increased 3.7 percent per year and 28.4 percent overall, from 482,600 in 2008 to 632,300 in 2015.

During this period, the population of MSM age 55 and older living with HIV more than doubled, swelling by 12.1 percent per year, from 62,400 to 139,700. This demographic shift represents another reason to celebrate but raises concerns about the readiness of clinicians to treat aging-related conditions among the HIV population, especially considering how the virus may drive and exacerbate such health problems, including cognitive decline and cardiovascular, kidney and liver disease.

Among MSM, HIV prevalence increased 4.7 percent per year from 147,300 to 201,800 among African Americans; 4.8 percent per year, from 108,600 to 151,200 among Latinos; 2.2 percent per year, from 207,200 to 240,900 among whites; and 5.9 percent per year, from 7,400 to 11,000 among Asians.

The number of those living with the virus who contracted the virus through heterosexual sex increased 1.3 percent per year during the study period.

In contrast, HIV prevalence declined 1.3 percent annually among PWID, from 147,000 to 135,100. The shrinking of this population may be an effect of the multiple other health problems associated with injection drug use, untreated or poorly treated HIV among PWID as well as opioid overdose deaths.

Overall, the proportion of the HIV population that remained undiagnosed fell from 18.1 percent in 2008 to 14.5 percent in 2015.

Among MSM, the proprotion of those living with HIV who remained undiagnosed declined 3.4 percent per year during this period, from 21.3 percent to 16.7 percent. The decline in this proportion of people living with HIV that was not diagnosed was greatest among those age 55 and older, dropping 7.5 percent per year, from 7.1 percent to 4.2 percent; among those 13 to 24 years old the rate of those undiagnosed dropped 3.7 percent per year, from 70.3 percent to 52.2 percent.

The CDC researchers theorize that the decline in the HIV rate among young MSM might have been driven in part by the dropping rate of undiagnosed HIV among that population. However, their paper also indicates that young MSM who acquire the virus may often contract it from a partner who is considerably older, given the higher prevalence of the virus in older age brackets.

The rate of undiagnosed HIV among MSM living with the virus, broken down by race, saw the greatest decline among Asians, at a 6 percent per year drop, with 33.2 percent of Asians with HIV remaining undiagnosed in 2008, a figure that dropped to 20.5 percent in 2015. However, HIV-positive Asians’ rate of undiagnosed HIV in 2015 is still the highest among all major racial groups. Meanwhile, the rate of undiagnosed HIV dropped 4.1 percent per year among HIV-positive Blacks, from 26.4 percent to 19.6 percent; 3.4 percent per year among HIV-positive Latinos, from 25.5 percent to 20.1 percent; and 3.3 percent per year among HIV-positive whites, from 15.1 percent to 11.9 percent.

The study authors state that the lack of progress in reducing HIV incidence among Black MSM and the rising transmission rate among their Latino counterparts “may be the result not only of a higher prevalence and percentage of undiagnosed infections but also lower viral suppression levels in these groups. Smaller percentages of Blacks/African Americans and Hispanics/Latinos with HIV infection are promptly linked to [HIV medical] care after diagnosis compared with other groups.”

They concluded: “Expansion of HIV screening to reduce undiagnosed infections and increased access to care and treatment to achieve viral suppression are critical to reduce HIV transmission. Access to prevention methods, such as condoms and pre-exposure prophylaxis [PrEP], is also needed, particularly among MSM of color and young MSM.”

At this year’s CROI in Boston, multiple studies, including one from the CDC, painted in stark relief how PrEP use is, in fact, falling short among those very communities.

To read the study abstract, click here.