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Per-contact Probability of HIV Transmission in Homosexual Men in Sydney in the Era of HAART

Per-contact Probability of HIV Transmission in Homosexual Men in Sydney in the Era of HAART. Fengyi Jin 1,2 , James Jansson 1 , Matthew Law 1 , Garrett Prestage 1 , Iryna Zablotska 3 , John CG Imrie 3 , Susan C Kippax 3 , John M Kaldor 1 , Andrew E Grulich 1 , David P Wilson 1

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Per-contact Probability of HIV Transmission in Homosexual Men in Sydney in the Era of HAART

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  1. Per-contact Probability of HIV Transmission in Homosexual Men in Sydney in the Era of HAART Fengyi Jin1,2, James Jansson1, Matthew Law1, Garrett Prestage1, Iryna Zablotska3, John CG Imrie3, Susan C Kippax3, John M Kaldor1, Andrew E Grulich1, David P Wilson1 1NCHECR, UNSW; 2STIRC, USYD; 3NCHSR, UNSW; 18th International AIDS Conference, Vienna July 2010

  2. Methods: the HIM study Risk factors Unprotected anal intercourse Circumcision status HIV diagnosis Per-contact risk Overview

  3. Most studies on per-contact probability of HIV risk focused on heterosexuals Only one prospective estimate 0.82 (0.24-2.76) per R-UAI (Vittinghoff, Am J Epi 1999) None data on estimate in the era of HAART Per-contact probability study in homosexual men more difficult Relationships are often non-monogamous Men can take either insertive or receptive role in anal intercourse Background

  4. HIV negative homosexual men in Sydney Community-based Recruitment 2001-2004 Follow up to June 2007 Two interviews per year Annual HIV testing Methods: the HIM cohort

  5. Number of episodes of UAI By partners’ HIV status (negative, positive and HIV status unknown) By sexual positioning (insertive vs receptive) Insertive UAI: whether participant circumcised Receptive UAI: whether ejaculation inside rectum occurred Circumcision status Risk factors

  6. Demographics • 1427 men enrolled • Retention rate: 87% (1 year); 81% (2 years) • Median age: 35 (18-75) • Median follow-up time: 3.9 years • 95% self-identified as gay or homosexual • 66% self-reported being circumcised

  7. 53 HIV seroconversions during the study HIV incidence 0.78 per 100 person-years 1136 men reported at least one episode of UAI 46 HIV seroconversions A total of 228,056 episodes of UAI HIV incidence

  8. UAI distribution No: Number of episodes

  9. UAI distribution No: Number of episodes

  10. UAI distribution No: Number of episodes

  11. UAI distribution No: Number of episodes

  12. UAI distribution No: Number of episodes

  13. UAI distribution No: Number of episodes

  14. UAI distribution No: Number of episodes

  15. UAI distribution No: Number of episodes

  16. UAI distribution No: Number of episodes

  17. UAI distribution No: Number of episodes

  18. Likelihood function development Based on binomial expression of probabilities Includes Number of episodes of UAI Circumcision status HIV seroconversion Number of episodes of UAI weighted by assumption of HIV prevalence Reported HIV negative partner 0.5% Reported HIV status unknown partner 10% Sensitivity analysis HIV negative partner (0.5-2%) HIV status unknown partner (5-15%) Per-contact risk calculation (1)

  19. Maximised likelihood function Estimate of probabilities for each exposure type Bootstrapping method 10,000 simulations Estimate confidence interval Per-contact risk calculation (2)

  20. Per-contact HIV risk

  21. Different scenarios

  22. R-UAI with ejaculation Twice as risky as R-UAI with withdrawal I-UAI in uncircumcised 10 times as risky as I-UAI in circumcised Summary

  23. Per-contact probability of HIV transmission due to R-UAI was similar to that of pre-HAART era Surprising given the following High HIV testing rates >90% ever tested >60% tested in the last year High HIV treatment coverage 70% diagnosed receiving HAART 75% on treatment have undetectable viral load Discussion

  24. Primary HIV infection in undiagnosed individuals is of primary importance Undiagnosed HIV infections higher than expected HIV transmission due to anal intercourse not as closely related to plasma viral load as in vaginal transmission The role of other STIs Why per-contact risk not decreased?

  25. Acknowledgements The authors wish to thank all the participants, the HIM study team and participating clinics for their contribution to this project. The project was funded by the New South Wales Health Department (Sydney), the National Institutes of Health, a component of the U.S. Department of Health and Human Services (NIH/NIAID/DAIDS: HVDDT Award N01-AI-05395), the National Health and Medical Research Council (#400944). The project was also funded by the Australian Government Department of Health and Ageing (Canberra). The views expressed in this presentation do not necessarily represent the position of the Australian Government.

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