Rapid rises in diagnoses in US gay men concentrated in black and younger men

By Roger Pebody

The number of HIV diagnoses continues to rise in American gay men and other men who have sex with men (MSM), with especially rapid increases seen in young black men, according to figures released by the Centers for Disease Control and Prevention (CDC) in the June 27^th edition of the Morbidity and Mortality Weekly Report.

The CDC tracked new diagnoses of HIV from 2001-2006, and calculated the estimated annual percentage change in diagnoses. For gay men and other MSM, the annual rise was 1.5%.

The analysis covers the 33 states that had a system of confidential, name-based HIV case reporting throughout the five year period. This includes a number of states with large gay populations, including New York, Florida and Texas, but not others such as California and Illinois.

During this time, a total of 214,379 people were newly diagnosed with HIV, and 46% of the diagnoses were in gay men and other MSM. There were statistically significant decreases in diagnoses for all transmission categories apart from gay men and other MSM. For example, there was a 4.4% annual decrease for heterosexuals, and a 9.5% annual decrease for injecting drug users.

However, diagnoses in gay men and other MSM increased by 1.5% each year (95% CI: 0.8 – 2.1), or 8.6% over the five year period. Moreover, there were marked variations in the increase in diagnoses in gay men and other MSM, according to race and to age.

Annual increases in black men and in Hispanic men were both 1.9%, in contrast to 0.7% seen in white men. A total of 36% of all diagnoses were in black men, although only 12% of the US population is black.

Moreover, the estimated annual increase in Asian and Pacific Island men was 12.1%. However as the total number of infections remains low in this group, the confidence intervals for this figure are relatively wide (95% CI: 5.0 – 19.6).

In terms of age, there were particularly large increases in diagnoses amongst the youngest men in all ethnic groups. For men aged 13-24, looking at all ethnicities together, the increase each year was 12.4%. A particularly large annual increase was seen in young black men – 14.9%, amounting to 93.1% over the five years.

Although the greatest increases were in the youngest men, this group only contributed 14% of the total number of diagnoses. As has long been the case, the majority of diagnoses occurred in the 25-44 age group. However the trends here are more encouraging, with an annual decrease of 1.1%, and decreases concentrated in both white and black men.

Diagnoses increased amongst those aged over 45, however, rising by 2.7% each year. There was a particularly marked increase of 3.8% in white men of this age group (compared to the increase of 0.7% for white men of all ages).

Finally, there were large variations according to region, with greater increases in the South and the Midwest.

During this period, and in contrast to the UK, the US reporting system was not set up to provide accurate measures of HIV incidence (i.e. the rate of new infections in the population). However this data does strongly suggest that incidence is rising in many groups of American men who have sex with men, and may be higher than previously estimated.

At the Conference on Retroviruses and Opportunistic Infections earlier this year, Ron Stall of the University of Pittsburgh had said that his systematic review of incidence studies concluded that incidence in community samples of American gay men was around 2.4% a year. Moreover, Stall went on to demonstrate the long term implications of such an incidence rate.

Taking this figure as a starting point, Stall ran a mathematic model to see how this incidence in a group of 18 year-olds would translate into HIV prevalence as the group got older. The key assumptions of the model were that each year 2.4% of the group acquired HIV, and that mortality rates were the same as for equivalent age groups in the general population.

By age 20, around 5% of the group would be HIV-positive; by age 25, around 15% would have HIV; by age 30, around 25% would be living with HIV, and when they were 40, 41% of the group would be HIV-positive.

Moreover, Stall re-ran the model for black men, based on a “low” estimate of 4% incidence in this group. The results were even more alarming: by age 40, around 60% of the group would have HIV.

Stall commented that he was “horrified” by these estimates. However he concluded that “at the HIV incidence rates we're already seeing in the published literature, we can expect an ongoing HIV epidemic among gay men that will yield high prevalence rates over time.”

Commenting on the CDC figures to the New York Times, Jennifer Hecht of the Stop AIDS Project in San Francisco said: “The high rates we see among black men and other minorities indicate that it’s very much connected to larger issues like poverty and racism.”