Objective Young men who have sex with men (MSM) and MSM of LRRC48 antibody color have the highest HIV incidence in the US. an HIV seropositive unknown HIV serostatus or an HIV seronegative partner. We used regression standardization to estimate average PCRs for each type of contact with bootstrap confidence intervals. Results The estimated PCR was highest for URA with an HIV seropositive partner (0.73%; 95%BCI 0.45%-0.98%) followed by URA with a partner of unknown HIV serostatus (0.49%; 95%BCI 0.32%-0.62%). The estimated PCR for UIA and PRA with an HIV seropositive partner was 0.08% (95%BCI 0.0%-0.19%) and 0.22% (95%BCI 0.05%-0.39%) respectively. Average PCRs for UIA and URA with HIV seropositive partners were higher by 0.14-0.34% among younger participants and higher Rucaparib by 0.08% for UIA among Latino participants compared to White participants. Estimated PCRs increased with increasing number of sexual partners use of methamphetamines or poppers and history of sexually transmitted infection. Conclusions Susceptibility or partner factors may explain the higher HIV conversion risk for younger MSM some MSM of color and those reporting individual risk factors. is an indicator for seroconversion for participant at visit is the PCR for contact type = 1 . . . is the true number of contacts of type reported by the participant at that visit. Infection risk is the complement of the probability of escaping infection on all contacts. The basic Bernoulli model also assumes that the PCRs are constant for each type of contact an assumption that almost surely does not hold. Hughes = 1 recently . . . seroconversion risk for participant at visit is estimated with all contact covariates and counts at their observed levels. The risk for participant at visit is estimated assuming no contacts of type is the PCR for contact type for that participant-visit and are defined as before. This equation means that the probability of escaping infection given observed levels of exposure equals the potential probability of escaping infection from all kinds of exposure multiplied by the probabililty Rucaparib of escaping infection from all contacts of type for values of 0. {The marginal PCR λis then calculated as average of the {λ0.|The marginal PCR λis calculated as average of the λ0 then. Marginal PCRs for subgroups defined by age race/ethnicity numbers of partners substance use and STD are obtained by averaging over appropriate subsets of the {λand is increased by covariates including age race/ethnicity numbers of contacts substance use and STD. Footnotes Conflicts of Interest and Sources of Funding: The authors report no conflicts of interest. Meeting where data were presented: Conference on Retroviruses and Opportunistic Infections; Atlanta; March 2013 Rucaparib 1 E Douglas J Judson F McKirnan D MacQueen K Buchbinder SP. Per-contact risk of human immunodeficiency virus transmission between male sexual partners. Am J Epidemiol. 1999 Aug;150(3):306-311. 2 F Jansson J Law M et al. Per-contact probability of HIV transmission in homosexual men in Sydney in the era of HAART. AIDS 2010;24:907-13. 3 JP Baeten JM Lingappa JR et al. Determinants of per-coital-act HIV-1 infectivity among African HIV-1-serodiscordant couples. J Infect Dis 2012;205:358-65. 4 NP Shiboski SC. Statistical analysis of HIV infectivity based on partner studies. Biometrics 1990;46:1133-50. Publisher’s Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a ongoing service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting typesetting and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content and all legal disclaimers that apply to the journal pertain. REFERENCES 1 CDC HIV Surveillance Report 2009 [July 7 2012 of Health and Human Services. 2011 2 CDC Estimated HIV incidence in the United States Rucaparib 2007 HIV Surveillance Supplemental Report 2012. 2012;17(4) 3 Buchbinder SP Vittinghoff E Heagerty PJ et al. Sexual risk nitrite inhalant use and lack of circumcision associated with HIV seroconversion in men who have sex with men in the United States. J Acquir Immune Defic Syndr. 2005 May;39(1):82–89. [PubMed] 4 Millett GA Flores SA Peterson JL Bakeman R. Explaining disparities in HIV infection among black and white men who have sex with men: a meta-analysis of HIV risk behaviors. AIDS. 2007 Oct;21(15):2083–2091. [PubMed] 5 Millett GA Peterson JL Flores SA et al. Comparisons of.