Risk Factors for HIV Seroconversion in a Contemporary Cohort of High Risk Men Who Have Sex with Men (MSM)

Background: To evaluate risk factors associated with HIV seroconversion among high risk MSM.

Methods: The HIVNET Vaccine Preparedness Study enrolled 3257 HIV negative MSM from 6 U.S. cities. Risk behavior interviews and HIV testing and counseling occurred semiannually for 18 months. Seroincidence was calculated using person-year (py) methods. Repeated measures logistic regression was used to estimate and test associations of serostatus at each 6-month visit with both time-independent and -dependent covariates.

Results: HIV seroincidence was 1.54/100 py (95% C.I. 1.22-1.94), with pairwise differences by city (lowest 0.8/100 py; highest 2.2/100 py) but not over time. On bivariate analysis, men < 35 years at enrollment (1.9/100 py) were significantly more likely than men > 35 (1. 1/100 py) to seroconvert. African-American (2.0/100 py) and Latino (1.9/100 py) MSM were somewhat but not significantly more likely than white MSM (1.3/100 py) to seroconvert. Independent predictors in the multivariable model controlling for city, age, and race were:

Risk behaviors, any 6-month period	% cohort	% seroconverters	Adjusted OR	(95% CI)
unprotected receptive anal sex w/ HIV	+2%	18%	4.75	(2.17 - 10.39)
unprot. receptive anal w/ HIV unknown	7%	25%	2.42	(1.35 - 4.33)
total male partners <5	1022%	28%	2.66	(1.11 - 6.40)
total male partners >5	1021%	41%	3.53	(1.45 - 8.55)
uncircumcised	13%	21%	2.15	(1.15 - 4.01)
amyl nitrate use	27%	52%	1.88	(1.12 - 3.15)

Conclusions: These data suggest that risk reduction counseling for MSM should focus on reducing unprotected anal sex with unknown serostatus as well as HIV + partners and address the total number of sex partners. Lack of circumcision appears associated with seroconversion in this U.S. population; whether this suggests the insertive route as a portal of entry is unclear. Amyl nitrate may enhance infection via behavioral or biological routes (e.g. increased trauma, increased blood flow). Seroincidence in this cohort is not declining over time.

Susan Buchbinder
San Francisco Dept. of Public Health
25 Van Ness Avenue, Suite 500
San Francisco, California 94102