Men Who Have Sex With Men Have a 40-Fold Higher Risk for HIV, Syphilis

Emma Hitt, PhD

March 11, 2010

March 11, 2010 (Atlanta, Georgia) — Approximately 7% of the American male population reports that they have ever had sex with another male, according to an analysis by the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

The finding enables the calculation of HIV and syphilis rates for this risk group and suggests that rates of these sexually transmitted infections among men who have sex with men (MSM) are at least 40 times higher than among other men or women.

David W. Purcell, JD, PhD, from the CDC's Division of HIV/AIDS Prevention, reported the findings at a late-breaking session here at the 2010 National STD Prevention Conference.

"This first-of-its-kind CDC analysis provides a new look at the stark disparities in HIV and syphilis rates among men who have sex with men, compared with other men and women," Dr. Purcell told Medscape Infectious Diseases. "While we've known that MSM make up the majority of the HIV epidemic, the new analysis allows us to put numbers to the disproportionate impact of HIV and syphilis in the gay community," he added.

The CDC first estimated the population size of MSM in the United States, then estimated HIV and syphilis rates in this group, and then compared these rates with those of other men and women.

The researchers searched the literature and identified 7 surveys involving nationwide American samples. Data were pooled based on recall period and then applied to census data to generate a population-sized estimate.

The CDC estimates that MSM comprise 2.0% (range, 1.4% to 2.7%) of the overall population in the United States aged 13 and older, or 4% of American men (range, 2.8% to 5.3%).

The data differed by recall year, however. The proportion of males who had engaged in same-sex behavior within the previous year was 2.6% (95% confidence interval [CI], 2.2 - 2.9), and within the previous 5 years was 4.0% (95% CI, 2.8 - 5.3); 7.0% of men stated that they had ever had sex with another male.

Using the 5-year recall period rate of 4%, Dr. Purcell and colleagues estimated that the rate of new HIV diagnoses among MSM was more than 44 times that of other men and more than 40 times that of women. The range was 522 to 989 cases of new HIV diagnoses per 100,000 MSM, compared with 12 per 100,000 other men and 13 per 100,000 women.

Similarly, the rate of primary and secondary syphilis among MSM was more than 46 times that of other men and more than 71 times that of women. The range was 91 to 173 cases per 100,000 MSM, compared with 2 per 100,000 other men and 1 per 100,000 women.

"This analysis is just a first step," Dr. Purcell said. "CDC is developing further breakdowns of MSM rates by race and age, as well as estimates for other populations significantly affected by HIV, such as injection drug users."

According to a related written release, CDC is implementing an updated National Syphilis Elimination Plan in cities where MSM have been hardest hit by the disease, and will release an updated HIV prevention strategic plan within the next year to support the President's upcoming National HIV/AIDS Strategy.

"These findings are very much what I would expect and are very credible," said Willi McFarland, MD, PhD, MPH, from the San Francisco Department of Public Health, and associate professor of epidemiology and biostatistics at the University of California, San Francisco. "There is a global conventional wisdom that the proportion of adult MSM falls between 2% and 5% when speaking of nations and large areas as a whole," he told Medscape Infectious Diseases.

"It is reaffirming to see that a synthesis of surveys produces estimates that fall within this range, and it may even explain some of the variation based on the time frame," he said.

However, Dr. McFarland points out that the nature of the calculation may be "one dimensional" when it comes to human sexuality and dealing with behavior alone.

"In addition to same-sex behavior, there is also same-sex attraction and sexual identity," he said. "A simple single number may belie the complexities of human sexuality and how we all fall on some spectrum of these factors, and may move in between them. Estimates of 2.6% to 7.0% understate all this."

Dr. McFarland added that it is important that clinicians and their patients strive to be comfortable discussing sexual orientation, sexual behavior, and their related health implications.

The study was supported solely by the CDC. Dr. Purcell and Dr. McFarland have disclosed no relevant financial relationships.

2010 National STD Prevention Conference (NSTDP): Abstract LBc. Presented March 10, 2010.


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