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Session 56 Poster Session Acute Infection: Resistance, Fitness, and Transmission Session Time: 4:30-6:30 pm Room 4E-F

366-M. Estimating Transmission Probabilities over Time in Acute HIV Infection from Biological Data C. Pilcher*1, H. Tien1, P. Stewart1, P. Vernazza2, H. Chakraborty3, J. J. Eron1, and M. Cohen1 1Univ. of North Carolina, Chapel Hill; 2Univ. Hosp., St. Gallen, Switzerland; and 3Emory Univ., Atlanta, GA Background: Per-coital act transmission probabilities have been defined in chronic but not acute HIV infection. Work in non-human primates suggests a parallel relationship between semen and blood viral loads over time during acute HIV infection. We have previously described a probabilistic model estimating male-female transmission as a function of total semen R5 HIV count and endocervical CD4+CCR5+ receptor availability. We assessed the impact of predicted changes in semen HIV concentration during acute HIV infection on per-coital act transmission probability. Methods: Blood HIV dynamics were described using longitudinal RNA levels from symptomatic acutely infected individuals not on antiretroviral therapy. An average fitted curve was generated using piecewise regression. The blood model assumed a median incubation period of 14 days, initial inoculum of 10-6copies/mL and static set point concentration. Predicted semen HIV dynamics were calculated based on this curve and observed semen RNA concentrations at set point. A fixed concentration ratio between semen and blood from initial infection to set point was assumed. From predicted semen concentrations, per-act male-female transmission probabilities were calculated using our published model given 100% R5 populations in semen, median endocervical CD4+CCR5+ receptor count and median ejaculate volume. Conclusions: 153 data points from 33 subjects contributed to the blood viral dynamic model. Peak viremia was at 24 days from infection. Semen HIV dynamics and transmission probabilities were estimated for hypothetical individuals with observed minimum, median and maximum set point semen RNA concentrations (2.17, 3.85, and 7.12 log copies/mL). Respective per-act probabilities of 0.0015, 0.0308, and 1.000 at peak viremia corresponded to probabilities of 0.0001, 0 .0018, and 0.8484 at set point. Probabilities at peak viremia were 19.7-, 22.2-, and 1.4-fold increased over set point in these examples. Conclusions. Susceptible partners of individuals with acute HIV infection may be at 20-fold greater risk per exposure compared to partners of individuals at virologic set point due to higher HIV shedding in semen.

©2002 9th Conference on Retroviruses and Opportunistic Infections