CROI 2011: Rectal Microbicides to Prevent HIV Infection in Heterosexual Populations in High-prevalence Settings

Poster from CROI 2011

Dobromir Dimitrov*1, M-C Boily2, S Abdool Karim3, and B Mâsse1,4
Fred Hutchinson Cancer Res Ctr, Seattle, WA, US; 2Imperial Coll London, UK; 3Univ of KwaZulu-Natal, Durban, South Africa; and 4Univ of Montreal, Canada


Background:
The role of anal intercourse in the overall heterosexual HIV epidemic remains unclear. However, it may be an important risk factor because the considerably higher risk of HIV infection during unprotected receptive anal intercourse compared to vaginal intercourse. Anal intercourse is widely practiced by heterosexuals in many countries; in Tanzania, 6% of sexually active school pupils reported anal intercourse at their first sexual experience. In Cape Town, 10 to 14% of the study participants reported engaging in anal intercourse over the last 3 months. Different mathematical modeling studies have assessed the potential impact of a vaginal microbicide in heterosexual populations and of a rectal microbicide for homosexuals. However, none have assessed the potential impact of a rectal microbicide in heterosexual population. Our study aims to compare the potential impact of rectal, vaginal, and bi-compartment (i.e. applied vaginally and protective during vaginal and anal intercourse) microbicides to prevent HIV acquisition and transmission in heterosexual populations.

Methods:
Risk equations were used to determine under which conditions a rectal microbicide could be as useful as a vaginal microbicide. A transmission dynamic model was used to assess the population-level impact of the different microbicides in a variety of intervention scenarios and high HIV prevalence settings and to predict the fractions of new HIV infections prevented over fixed time periods.

Results:
Without anal intercourse, a 50% efficacious vaginal microbicide used by 100% of females prevents about 10% and 25% of all new male and female HIV infections over 10 years if adherence is 30% and 75%, respectively. These 10-year infection preventions are reduced by 32% in populations with 10% frequency of receptive anal intercourse, assuming 4-fold increase in transmission risk per receptive anal intercourse (RRRAI). A rectal microbicide could be as effective as a vaginal microbicide in populations with anal intercourse rates ranging from 5% to 20% across a range on RRRAI, assuming similar efficacy and frequency of use of both products. A rectal microbicide has less impact than a vaginal microbicide in populations with <5% anal intercourse, unless it is used more often or is more efficacious than a vaginal microbicide. The 10-year infections prevented of bi-compartment microbicide is 2-fold larger than vaginal microbicide in populations with 10% anal intercourse if RRRAI = 10- and ~6-fold larger than rectal microbicide, in populations with 5% anal intercourse if RRRAI = 4.

Conclusions:
Both rectal microbicide and bi-compartmental microbicide are necessary prevention tools for heterosexual populations engaging, relatively frequently (~10% of sex acts), in anal intercourse.


[If an item is not written by an IRMA member, it should not be construed that IRMA has taken a position on the article's content, whether in support or in opposition.]

No condom use after recent viral load test safer than intermittent condom use

From aidsmap, by Roger Peabody

In stable gay couples, where one partner is taking HIV treatment and the other is HIV-negative, the risk of HIV transmission is relatively low if condoms are not used following a recent undetectable viral load test result. However, using condoms on a few more occasions but without reference to viral load substantially increases the risk of HIV transmission.  These are the findings of a mathematical modelling study, drawing on detailed data on viral loads in Dutch gay men, published online ahead of print in Sexually Transmitted Infections.

The model suggests that during the entire period that a first-line treatment regimen is taken, the risk of HIV transmission would be 1% if condoms are used all the time, 3% if condoms are not used after an undetectable viral load test in the past six months, 17% if condoms are used 30% of the time, and 22% if condoms are never used.

The model was designed to test the proposition put forward in the Swiss statement: that in long-term, serodiscordant couples, a decision to give up using condoms can be safely made as long as the HIV-positive partner is adhering to HIV treatment and has had an undetectable viral load for at least six months.

Read the rest

Read the article in Sexually Transmitted Infections

Pre-exposure prophylaxis: cost-effectiveness dilemmas analysed by Australian study

via Aidsmap, by Gus Cairns

Pre-exposure prophylaxis would maintain HIV prevalence among high-risk gay men at the current level and prevent a prevalence increase of up to 5%, a mathematical model has shown, even if it were taken only half the time and only prevented one in two infections.

However for PrEP to significantly reduce HIV prevalence in this population it would need to be 90% effective and be taken continuously.

If prescribed in either of these two ways it would be barely cost effective. Intermittent PrEP could be more cost effective, but to be so it would need to have higher efficacy than yet demonstrated – around 90%.

The model was presented to the European AIDS Conference by Jonathan Anderson of the Australian National Centre in HIV Epidemiology and Clinical Research. He noted that past analyses of whether PrEP could be cost-effective, based on the US epidemic, had produced contradictory results.

Read the rest.

Click 'n Learn - Modelling the impact of a rectal microbicide

Dr. Rowena Johnston of amfAR and Dr. Anna Foss (pictured) of the London School of Hygiene and Tropical Medicine presented "Modelling the impact of a rectal microbicide used by men who have sex with men in Lima, Peru and Bangalore, India" for the last IRMA Global Teleconference of the year, held earlier today.

Foss's excellent slides are available on the IRMA website, in the Teleconference section.

You can also click the first slide below to download the entire set.

Modeling the impact of a rectal microbicide used by men who have sex with men in Lima, Peru and Bangalore, India

Join Dr. Rowena Johnston of amfAR (below) and Dr. Anna Foss (above) of the London School of Hygiene and Tropical Medicine (LSHTM) for the last IRMA Global Teleconference of the year:


Wednesday, December 10, 2008

**Location/Time:
Mexico City, Lima - 11:00 AM
New York, DC - 12:00 PM (noon)
London - 5:00 PM
Lagos - 6:00 PM
Bangalore - 10:30 PM
Bangkok - Midnight

Background:

In 2002, Dr. Charlotte Watts, Dr. Anna Foss and other colleagues at the LSHTM declared that if used in 50% of sex acts not protected by a condom, a vaginal microbicide that is 60% efficacious against HIV could avert 2.5 million infections over three years, if distributed in 73 low and middle income countries and coverage is 20% of groups in contact with services.

No such data exist outlining the potential impact of rectal microbicides on the epidemic, but such information could aid advocacy efforts aimed at increasing investment in rectal microbicide research. However, the scope for conducting a similar analysis is limited by the lack of data from low- or middle-income countries on the extent of anal sex, and its contribution to the HIV epidemic.

Using amfAR support, Dr. Foss will lead a research team plan to conduct mathematical modeling studies similar in concept to those used in the vaginal microbicide work described above, but focusing on two lower middle-income country settings, where there are adequate data for this modeling for MSM (Lima, Peru and Bangalore, India.)

Meet the Presenters:

As Vice President of Research at amfAR, Dr. Rowena Johnston is responsible for overseeing the Foundation’s pioneering research program. Her responsibilities include evaluating and analyzing the program’s direction, serving as a liaison to the Research Committee, Executive Committee, and Board of Trustees, organizing think tanks and symposia, and writing on current scientific topics.

Recently she has overseen the reorganization of amfAR’s research program specifically to target work directed at improving HIV prevention interventions, and to optimize treatment and pursue the potential of a cure for HIV infection. Rowena has also implemented changes that allow amfAR’s research program to support scientists working in a range of research disciplines, including basic biomedical, clinical, behavioral, social and policy areas.

Dr. Anna Foss, Lecturer in Mathematical Modeling, joined the London School of Hygiene and Tropical Medicine in July 2001 after graduating with a Masters of Mathematics from the University of Manchester. During the summer of 2000 she worked as a Research Assistant in the Epidemiology Department of the University of Manchester.

Anna is a member of the HIVTools Research Group and the Gender Violence & Health Centre. She has been working primarily on mathematically modelling the transmission of HIV and STIs, and the potential impact of current and future HIV/STI prevention interventions, among female sex workers, injecting drug users and men who have sex with men, in different settings. Anna is also currently working to link epidemiological modelling to social science research in order to explore questions around the importance of the relative mobility of sex workers and clients, and the increased risk of HIV transmission through rape.

Alongside this work, Anna completed a part-time staff-PhD, titled: 'Mathematical modeling of HIV/STI transmission and prevention: methodological issues when dealing with uncertainty'. More information about Anna's research and teaching can be found online.

**More information on this IRMA Global Teleconference will be available in the coming weeks. Members of IRMA will receive an invitation to join the call and will be supplied with dial-in instructions when they RSVP. You may join IRMA by clicking here. Click here for membership information.