PEPFAR: Epidemiologist presents a scientific rationale for focusing on Abstinence & Being Faithful in sub-Saharan Africa

“The high prevalence HIV epidemic in sub-Saharan Africa is characterised by close-knit sexual networks that allow the propagation of the virus to large numbers of individuals” said epidemiologist David Stanton, who believes that Abstinence, Being Faithful and Condoms-based (ABC) interventions, but especially the A & B parts, are the means to disrupt these networks. Stanton, who serves as the Chief of the Division of Technical Research in the Office of HIV/AIDS at USAID, made a scientific case in support of PEPFAR’s emphasis on A & B, at the 2006 Implementers meeting in Durban last month.

He concedes that the topic “has created more contention and sometimes animosity within the public health community than any other,” nevertheless, he believes that a growing body of data support the employment of A & B prevention efforts as the best way to interrupt the cycle of infection in sub-Saharan Africa.

The uniquely generalised epidemic of sub-Saharan Africa

The emergence of the generalised HIV epidemic in sub-Saharan Africa has frequently been attributed to dispersion from an initially localised epidemic, where high risk individuals have spread HIV into the general population. But this pattern hasn’t really emerged any where else in the world. One possible explanation could be differences in sexual behaviour but the numbers don’t really add up — the differences between the number of life time sex partners, risky sex acts or behavioural practices reported in sub-Saharan Africa versus other settings do not appear to be great enough to explain the dramatic differences in prevalence (or the speed of the epidemic's growth). (Although some researchers believe the difference could be physiological, see below).

However, although people in Africa do not report having a higher number of lifetime sexual partners, on average, than people in other parts of the world, according to some surveys, both men and women in Africa do commonly report having two or more concurrent sexual partners. This cultural phenomenon of ongoing concurrent partnerships is believed to be specific to Africa. Serial monogamy, perhaps with an occasional one night stand, is reportedly the norm in the West, while in the Asia, when there is sex outside of marriage, it is usually a one-off event with a sex worker.

This theory has also been described by several editorials in The Lancet (Halperin, Epstein 2004 and Shelton, Halperin, Wilson 2006), and in a couple of papers by Prof. Martina Morris, of the University of Washington.

Morris has developed mathematical models showing the sexual networks that form when people are in more than one concurrent partnership, and has found that even when the total number of life-time sexual partnerships is the same, HIV could be spread much more rapidly across populations where people have concurrent sexual partners than among populations where serial monogamy is the norm.

Africa caught in a web

Stanton presented some of these web-like models during his talk and pointed out that “these networks are extremely sensitive to the number of sexual partners, so that [with the addition of only a small number of extra partners], you start to see an extraordinarily dense network. It doesn’t take a large increase in the number of concurrent sexual partners to link a large number of people together.”

Stanton then referred to recent data from researchers Stephane Helleringer and Hans-Peter Kohler from the University of Pennsylvania, who have been documenting the existence of a large sexual network among the population of Likoma Island, in the northern region of Lake Malawi. In this remote and isolated region, Helleringer and Kohler surveyed everyone in seven villages who was in a sexual partnership, and found that, because of concurrent sexual partnerships, 65% of the 1070 people surveyed were all connected to each other in a sexual network.

“Most of these people had only two or three partners, but what you see here is a highly integrated sexual network of people who probably do not consider themselves to be at high risk because they only have a small number of multiple sex partners,” said Stanton.

Stanton also believes certain biological or physiological factors may serve as “amplifiers” for transmission: 1) the high infectivity associated with high viral loads during acute infection (which increases the likelihood of rapidly transmitting the virus across a sexual network), 2) the lack of male circumcision, which according to some studies may increase the likelihood of transmission 4-5 fold, and 3) herpes virus infection. However, Stanton made no reference to differences in HIV-1 subtypes, which according to some epidemiologists, may account for the very rapid spread of HIV-1C in southern Africa.

Of course, at present the jury is still out about the relative contributions of having concurrent multiple partners versus other amplifiers to high HIV prevalence in some countries. Despite the existence of an integrated sexual network in a remote part of Malawi, this has yet to be demonstrated in other countries such as South Africa.

Breaking the chains

Nevertheless, the data would seem to provide a compelling case to at least consider behavioural interventions, especially “B” interventions that reduce the number of concurrent sexual partnerships.

“Abstinence, fidelity, partner reduction, condom use are the tools to break apart these networks,” said Stanton.

Stanton believes that condom-based prevention efforts have their place — particularly where epidemics are still primarily localised in certain risk groups, such as sex workers and the men who visit them. He highlighted the example of south India, where a study has documented a reduction in HIV prevalence among women aged 15-24, which researchers have concluded is due to rising condom use by men and female sex workers India, and reduced transmission to wives (Kumar 2006).

“The expansion of condom use and education amongst sex workers remains a priority to control HIV-1 in India,” said Stanton. “But what works well in one epidemic does not necessarily work well in another, and I think condoms are the best example of that.” He presented data from Botswana that show an uptake in the use of condoms and rising condom sales and yet “the prevalence levels seem to be going nowhere.”

He attributes the failure of condom prevention efforts in this setting to the fact that it is very difficult to get people in long-term relationships to use them. In Botswana, there has been little change in the uptake of condoms by married women, and similar observations have been made in other countries. “When you get to married couples, it is difficult to get condoms in there,” he said. “Condoms have a hard time crossing the marriage and the relationship barrier.”

He also presented other data showing that if condom use is not consistent, it is much less effective. “Do we need to abandon condoms? Of course, not. But we need to differentiate between individual level interventions and those interventions that are likely to achieve population level impact,” Stanton added.

It might actually be easier to get people to reduce the number of their partners — once they know the risks for HIV that these sexual networks pose to themselves and their loved ones. Stanton believes that data from Uganda, Kenya and Zimbabwe, which have all shown reductions in the number of partners associated with reductions in prevalence, provide evidence that this approach works.

However, the changes in prevalence that are now being reported in some African countries must be interpreted cautiously, particularly in Zimbabwe where high rates of mortality and emigration could explain most of the reductions in prevalence (see related article). It is also important to note that HIV incidence peaked in most of sub-Saharan Africa years ago in the 1990’s, usually before any significant prevention campaigns were introduced, and changes in these behavioural indicators were recorded long after the actual declines in incidence (UNAIDS 2005).

In the recent Lancet editorial, Shelton, Halperin, and Wilson asked: “What caused these incidence declines? Most important surely are purely epidemiological phenomena—those most susceptible become infected first (because of sexual behaviour and networks) and the susceptible pool shrinks. Moreover, at some point the chain reaction derived from the infectiousness of newly-infected people subsides.”

Eventually, the rising mortality rate of people infected with HIV will surpass the stable incidence rate, and the prevalence will begin to level off, and — in countries without adequate access to antiretroviral therapy — decline. At this point, it will be all too easy for proponents of either side of the condom-centred versus A & B-only prevention debate to take the credit. But the true test for any prevention intervention will be whether it reduces incidence of new infections, or at least the prevalence in key age groups (for example, people aged 15-24 as in the Indian study).

Stanton presented some intriguing data along this line that had been presented earlier at the meeting by Dr. Vinod Mishra. Dr. Mishra’s study had found strong associations between having multiple partners and the risk of HIV transmission in a number of sub-Saharan African countries. In one analysis of people in long term relationships in Cameroon, statistically significant associations between HIV prevalence and fidelity were observed. Couples who had only one lifetime partner have a very low HIV prevalence, while people with multiple sex partners had a much higher HIV prevalence. However, couples who reported that they had been faithful to their partner in the last 12 months, also had a lower HIV prevalence than those with multiple sex partners. According to Stanton, this finding demonstrates the protective effect of becoming faithful to one partner.

Going beyond the data

Although Stanton’s presentation was fairly well grounded in data, he occasionally veered into the subjective in ways that seemed more tailored to pleasing those with a faith-based agenda. “We need to appreciate the overwhelming protective effect of abstinence when it is successful. I like to think of abstinence like [adherence to antiretroviral therapy]. If you can adhere to it, it works very well, but if you are abstinent sometimes and not others, it isn’t going to work, and you may not get a second chance.”

But while it is true that it is possible to become infected by just one sexual encounter, to imply that anything less than total abstinence until marriage will not avert most infections is absurd, and is setting the bar unnecessarily high. Any significant reduction in the number of partners or reduction in sexual risk taking could have a population level effect. And according to the very models that Stanton presented, even if Africans simply adopt serial monogamy or a pattern of sexual behaviour more like that practised in South-east Asia, by abandoning regular concurrent sex partners, and using condoms for one night stands or with sex workers, Africa’s generalised epidemic should become a thing of the past.