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Validation of urine collected after prostate massage for studies of male HIV-1 infectivity
S. Graham1,2,3,4, J. Krieger1, K. Ramko2, L. Wamuyu2, P. Githua2, S. McClelland1,3, N. Peshu2, J. Dragavon1, E. Sanders2,5, R. Coombs1
1University of Washington, Seattle, Washington, United States, 2Kenya Medical Research Institute, Kilifi, Kenya, 3University of Nairobi, Nairobi, Kenya, 4University of Toronto, Toronto, Ontario, Canada, 5University of Oxford, Oxford, United Kingdom
Background: Assessing male HIV-1 infectivity is difficult in many clinical settings or where semen collection by masturbation has poor acceptability. Because blood plasma viral load does not accurately predict seminal HIV-1 RNA levels, alternative genitourinary sampling methods are needed. We evaluated post-prostatic massage fluid/urine (post-PMF/U) HIV-1 RNA as a surrogate marker for seminal HIV-1 shedding.
Methods: HIV-1-seropositive Kenyan men were evaluated after 48 hours of sexual abstinence. At each visit, a clinician performed prostatic massage until expressed prostate fluid was visualized, then post-PMF/U and blood were collected. Participants provided a semen specimen one week later, again after 48 hours of abstinence. HIV-1 RNA was quantified using a real-time PCR assay; lower limits of quantification were 30 copies/mL in post-PMF/U and plasma, 750 copies/mL in semen. Linear regression compared log10-transformed semen and post-PMF/U HIV-1 RNA levels, adjusting for factors that may influence shedding. Longitudinal analysis with generalized estimating equations (GEE) was performed to evaluate change over 2 visits.
Results: Thirty men provided paired semen and post-PMF/U samples, including 11 (37%) on antiretroviral therapy. A model including both plasma viral load and post-PMF/U fitted this cross-sectional study best, with a change in log10 post-PMF/U RNA per change in log10 semen RNA of 0.75 (95% CI 0.40-1.10, p< 0.001, R2 = 0.67). Nineteen men provided samples at 2 visits. GEE analysis showed that log10 post-PMF/U RNA alone was the best predictor of log10 semen RNA (beta = 1.0, 95% CI 0.63-1.37, p< 0.001).
Conclusions: At a single visit, plasma viral load and post-PMF/U HIV-1 RNA levels accounted for 67% of the variation in seminal HIV-1 RNA levels. Over time, seminal HIV-1 RNA levels were more closely associated with post-PMF/U than with plasma viral load. For studies requiring repeated genitourinary sampling, post-PMF/U is a better surrogate for seminal HIV-1 infectivity than blood plasma.
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