Treatment News : Study Confirms Viral Load Most Important Predictor of HIV Transmission

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January 13, 2012

Study Confirms Viral Load Most Important Predictor of HIV Transmission

A new African study of heterosexual HIV-serodiscordant couples—in which one partner is positive and the other is negative—confirms that viral load is the most important factor influencing the risk of transmitting the virus, according to data published in the February 1 issue of The Journal of Infectious Diseases. The findings also stress the importance of other transmission variables, including condom use, age, male circumcision status and the presence of other sexually transmitted infections (STIs).

The primary goal of the study was to calculate the risk of HIV transmission per act of sexual intercourse with an HIV-positive partner in the absence of antiretroviral treatment, notably among heterosexuals in sub-Saharan Africa, who make up roughly two thirds of the world’s population of people living with HIV. According to study authors James Hughes, PhD, of the University of Washington and his colleagues, the average rate of infection was found to be 1 per 900 coital acts.

Though estimates of the probability of HIV infection per act of sexual intercourse can be confusing on a level of personal decision making—it only takes one unsafe sexual encounter to become infected with the virus—these estimates are of importance to experts in the field of HIV epidemiology and prevention. According to an editorial accompanying Hughes and his team’s paper, Ronald Gray, PhD, and Maria Wawer, MD, of Johns Hopkins University point out that these estimates are needed “for modeling the epidemic and for projecting the effects of preventive interventions.” Indeed, they add, these estimates “[have] been the holy grail of HIV epidemiology for [more than] two decades.”

Estimates, however, haven’t been consistent, given variations in the populations included in studies, including those residing in low- and high-income countries, male-to-female versus female-to-male transmission, stage of HIV infection in the positive partner, the effects of demographic and behavioral characteristics and STI cofactors.

In an effort to provide more consistent results, Hughes and his colleagues—including researchers in eastern and southern African—analyzed data from a study that included 3,297 HIV-discordant couples in South Africa, Kenya, Rwanda and Zambia who received either acyclovir or placebo to determine the effects of suppressing genital herpes, or herpes simplex virus-2 (HSV-2) infection, on HIV transmission rates. The couples had frequent follow-up to measure viral loads in the positive partner; this included genetic testing to link the transmitted virus to the HIV-positive partner in order to prevent including infections acquired from other possible partners.

Though the study did not find an association between acyclovir use and HIV transmission, it provided the researchers with the opportunity to estimate per coital HIV transmission, considering that antiretroviral therapy was only offered once the positive partner’s CD4 cell count fell below 250.

Overall, there were one to two incidents of HIV transmission per 1,000 acts of sexual intercourse—a rate similar to those found in other low-income countries, but higher than estimates from many industrialized countries.

The viral load in the original infected partner was the main driver of transmission, with the risk increasing 2.9 times for every log increase in viral load (for example, an increase from 10,000 copies to 100,000 copies). This finding was somewhat higher than previous estimates of transmission risk associated with viral load, possibly because the short follow-up intervals and frequent viral load measurements in the study allowed more precise estimates of the association between HIV levels and infectivity.

The study also confirmed that condoms are highly protective, reducing the risk of HIV transmission by 78 percent when volunteers self-reported condom use. “[This] suggests a very high rate of consistent use, which is atypical for married couples in sub-Saharan Africa,” Gray and Wawer note. 

Older age was also associated with reduced transmission per sex act, as has been previously reported, and male circumcision reduced female-to-male transmission by about 47 percent, an effect compatible with the efficacy reported in three randomized trials of circumcision for HIV prevention.

HSV-2 infection and genital ulceration increased transmission between 2 and 2.7 times, another confirmation of previous research findings.

The findings also showed that the risk of an HIV-positive man transmitting the virus to a negative woman was about twice the risk of an HIV-positive woman transmitting it to an HIV-negative man. However, this difference can be attributed to the difference in viral loads between men and women, the authors noted. After adjusting the data for viral load differences—the men in the study tended to have higher levels, on average—the male-to-female and female-to-male transmission rates per act of sexual intercourse were found to be similar. This finding differs from those in high-income countries, where the transmission risk from men to women is significantly higher, even after adjusting for viral load differences.

Differences in age and HSV-2 infection in the HIV-negative partners also help account for the gender disparity—the HIV-negative female partners were, on average, younger and had higher rates of genital herpes than their male counterparts.

“Our results underscore the importance of antiretroviral therapy”—findings underscored by the encouraging results of the HPTN 052 study—“and, possibly, treatment of coinfections, to reduce plasma HIV-1 viral load in HIV-1 infected partners, and condom promotion, male circumcision, and treatment of symptomatic sexually transmitted infections for HIV-1 uninfected partners as potential interventions to reduce HIV-1 transmission,” Hughes and his colleagues conclude.

Search: viral load, transmission, condoms, age, circumcision, men, women, heterosexuals, sexual intercourse, prevention, epidemiology, partners, Africa

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  comments 1 - 8 (of 8 total)    

Joe Parton, San Francisco, 2012-04-29 00:42:19
What is it with every article on transmission of HIV slipping in "oh yeah and cut off half the skin of the dudes penis"? Seriously? HARRT reduces transmission, condoms reduce transmission, but just in case let's mutilate the penis as good measure. I've commented before on articles and will say it here again -- male circumcision will do more harm than good. After undergoing the torment of genital mutilation men will then be less likely to see the need to use a condom which work nearly 100%.

jecinta mwikali, nairobi, 2012-01-24 23:07:20
nice and educative article. God bless the poz team for updating us

Tim Horn, New York, 2012-01-20 09:26:45
Brent, remember, this study only involved those not on ARV treatment, thus nobody had undetectable viral loads. Basically, this study looked at risk of transmission in UNTREATED heterosexual serodiscordant couples.

Zinger, this is actually an analysis from a study looking at the effects of herpes treatment of HIV transmission. The study wasn't conducted to look specifically at viral load and transmission. You're right. We knew this. And we used data from this study to confirm it.

Bent, Washington,DC, 2012-01-17 23:43:28
The viral load in the original infected partner was the main driver of transmission, with the risk increasing 2.9 times for every log increase in viral load.

So what is the rate for those with no detectable VL? Notice they never say what the transmission rate is. It's the dirty little secret of the HIV/AIDS prevention community. I understand why they hide the truth but it does not generate a lot of faith. Maybe the new CCR5 studies will make this moot.

Tom Tobin, MA, 2012-01-15 12:34:09
The easiest way to keep down the viral load is not circumcision. It's using a condom. Condoms are measurably more effective. If you use condoms, there is no need to lose 60% or more of the nerves of the genitals of a male. Circumcision has not been demonstrated to prevent a single disease.

Zinger, , 2012-01-14 12:20:36
Wow, medical science is pedantic! How much money did we waste proving the obvious this time?

Mark Lyndon, , 2012-01-13 18:27:55
In 6 African countries, men are *more* likely to be HIV+ if they've been circumcised - Cameroon, Ghana, Lesotho, Malawi, Rwanda, and Swaziland. Eg in Malawi, the HIV rate is 13.2% among circumcised men, but only 9.5% among intact men. If circumcision really worked against AIDS, this just wouldn't happen. The one RCT into male-to-female transmission showed a 54% higher rate in the circumcised group btw. ABC is the way forward. Promoting circumcision will cost African lives, not save them.

Ronald Goldman, Ph.D., Boston, MA USA, 2012-01-13 16:57:03
Many professionals have criticized the studies claiming that circumcision reduces HIV transmission. They have various flaws. The absolute rate of HIV transmission reduction is only 1.3%, not the claimed 60%. Circumcision causes physical, sexual, and psychological harm. Other methods to prevent HIV transmission (e.g., condoms and sterilizing medical instruments) are much more effective, much cheaper, and much less invasive. Please see for links to literature.

comments 1 - 8 (of 8 total)    

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