Rectal gonorrhea and early syphilis led all sexually transmitted infections (STIs) in predicting incident HIV infection, according to results of a nearly seven-year study in Washington of 6,577 men who have sex with men (MSM). Using methamphetamine or inhaling nitrites doubled HIV risk in these men, according to the study.
Because risk factors for HIV infection and other STIs largely overlap, an STI diagnosis has proved a consistent prelude to HIV infection. Sexually active MSM run a disproportionate risk of acquiring STIs and account for most new HIV infections in the United States and many countries with similar HIV epidemics. Understanding which STIs precede HIV infection most often could help health professionals target the most at-risk men for prevention, including pre-exposure prophylaxis (PrEP).
To provide a more precise ranking of STI precursors to HIV infection, researchers from the University of Washington and other centers analyzed STI and HIV surveillance data on MSM across the state of Washington from January 2007 through June 2013. The investigators could chart HIV incidence according to prior STI diagnoses because the state routinely matches STI surveillance data to HIV surveillance data. The analysis included HIV-negative MSM or men with unknown HIV status who were diagnosed with syphilis, chlamydia or urethral, rectal or pharyngeal gonorrhea, which represent 98% of reported STIs. Washington State requires all providers to complete a case report for any person diagnosed with syphilis, gonorrhea or chlamydia.
The analysis involved 6,577 HIV-negative or status-unknown MSM who had 10,080 reported bacterial STIs between January 2007 and June 2013. The study group had a median age of 28 years (interquartile range 23 to 37), 60% were white, 15% Hispanic, 9% black and 6% Asian or Pacific Islander.
Through a median 2.4 years of follow-up, 280 of these 6,577 men (4.3%) were diagnosed with HIV infection. Those new HIV infections yielded an incidence of 1.61 cases per 100 person-years, a rate that quadruples the statewide HIV incidence among MSM (0.41 per 100 person-years). Of the 280 men who became infected with HIV, 221 (79%) tested negative for HIV when diagnosed with their STI or at a later point.
HIV incidence was greatest after rectal gonorrhea (4.1 per 100 person-years), followed by early syphilis (2.8), urethral gonorrhea (1.6), rectal chlamydia (1.6), pharyngeal gonorrhea (1.1), late syphilis (1.0) and urethral chlamydia (0.6). If PrEP lowers HIV risk 44% in MSM, 55 men diagnosed with rectal gonorrhea and 80 diagnosed with early syphilis would have to be treated with PrEP for one year to prevent one new HIV infection. If PrEP lowers HIV risk 92% in MSM, those numbers would fall to 26 for rectal gonorrhea and 38 for early syphilis.
At publicly funded testing programs, HIV incidence after STI diagnosis reached 2.48 per 100 person-years, 54% higher than the 1.61 incidence in the primary analysis.
Among 3715 men (56% of 6,577) with substance use data from at least one STI diagnosis, 17% inhaled nitrites, 11% used erectile dysfunction drugs and 8% used methamphetamine in the year before their STI diagnosis. Bivariable analysis determined that HIV incidence was higher in men who used methamphetamine than in those who did not (5.09 versus 1.65 per 100 person-years), in those who inhaled nitrites than in those who did not (4.40 versus 1.53), and in those who used erectile dysfunction drugs than in those who did not (3.91 versus 1.71) (P < .001 for all). Multivariable analysis including all three substances determined that methamphetamine and inhaled nitrites were associated with a doubled risk of HIV infection (adjusted hazard ratio 1.92 for methamphetamine and 2.2 for nitrites, P < .001 for both).
The researchers conclude that MSM diagnosed with rectal gonorrhea or syphilis -- particularly those who use methamphetamine or nitrites -- run a high risk of HIV infection. Because gonorrhea and syphilis are reportable across the United States, the authors propose that MSM with these STIs "could be targeted by public health agencies for specific prevention outreach, particularly promoting frequent HIV/STI testing and PrEP." They urge clinicians to discuss PrEP with MSM diagnosed with rectal gonorrhea or early syphilis and with MSM who report using methamphetamine or nitrites.