D for death, not A B or C, is main cause of decline in Ugandan HIV prevalence

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Mortality, not behavioural change, is the main cause of the decline in HIV prevalence seen in Uganda during the last decade, a study from the Rakai district suggests.

In a late breaker presented at the Twelfth Annual Retrovirus Conference, Maria Wawer of Columbia University in New York said that increased deaths due to AIDS contributed 5% of the 6% decline in prevalence seen in the Rakai district between 1993 and 2004.

Annual incidence had not declined during the same period, and prevalence among young people under 19 had also not changed.


risky behaviour

In HIV, refers to any behaviour or action that increases an individual’s probability of acquiring or transmitting HIV, such as having unprotected sex, having multiple partners or sharing drug injection equipment.

mathematical models

A range of complex mathematical techniques which aim to simulate a sequence of likely future events, in order to estimate the impact of a health intervention or the spread of an infection.


A type of virus that uses of RNA as its genetic material. After infecting a cell, a retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA (the hereditary material in humans). The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. HIV is a retrovirus. 


The study of the causes of a disease, its distribution within a population, and measures for control and prevention. Epidemiology focuses on groups rather than individuals.


A serodiscordant couple is one in which one partner has HIV and the other has not. Many people dislike this word as it implies disagreement or conflict. Alternative terms include mixed status, magnetic or serodifferent.

She also found that while condom use has increased sharply over the last ten years, this has been counterbalanced by increases in other sexual risk behaviour and that Ugandans, at least in Rakai, appear to be less abstinent and less faithful than they were.

The implication is that if HIV treatment starts to reduce mortality in the area, HIV prevalence may actually increase, following a pattern seen in parts of the developed world. These findings are especially important in the context of debates over the relative contributions of A, B, and C - abstinence, behaviour change and condoms - to containment of the HIV epidemic in resource-limited settings.

Wawer was presenting findings from the Ugandan Open and Positive Programme, which has conducted continuous surveillance of HIV incidence and prevalence (via blood tests) and sexual behaviour (via questionnaires) of 44 communities in the Rakai district since 1993.

Wawer said HIV prevalence during that time had declined from about 20 to 13% in women and from 15 to 9% in men.

However the incidence of new cases had not change. It was 1.3% a year in 1993 / 4 and 1.7% in 2003 / 4, a non-significant difference.

Condom use had increased among men and women significantly during that time. For instance, in male teenagers (15 - 19) with casual partners it had doubled from 19 to 38%.

Women reported using condoms 28% of the time among non-married partners but only 1% of the time with husbands.

However other sexual risk-taking behaviour had increased. Forty per cent of 15 to 19 year-old males were sexually active in 1993 / 4. This had increased to 50% by 2003 / 4.

The number of men (aged 15 - 49) reporting two or more sexual partners in a year increased from 22 to 27% in the decade.

Of particular concern was that 48% of men diagnosed with HIV during 1993 / 4 reported two or more sexual partners. This had increased to 69% in 2002 / 3. Wawer commented that there was no way of telling if extramarital sexual activity was a cause of, or subsequent to, their HIV infection.

Given a flat incidence rate, the main cause of the decrease in prevalence was death. The mortality rate due to AIDS increased in Rakai from 12% in 1990 to 14% in 2002. In 2001 to 2003 there were 125 new cases of HIV among the study population, and 200 deaths. Death therefore contributed to more than 80% of the decline in prevalence.

She did acknowledge in response to a question that prevalence had already started to decline during the late 1980s but said that incidence had been no higher during those years and that behavioural change probably contributed no more then than it did now.

E and F?

Wawer added that the increase in sexual risk behaviour among newly infected men was of particular concern. ‘E’ for epidemiological modelling among the study population had revealed that the HIV transmission rate per sex act was eight per 100,000 from newly infected partners (corresponding to a 2% annual incidence rate in the negative partner in a serodiscordant couple if they had sex every other day), but less than two per 100,000 from chronically infected individuals.

In terms of F for the future, she added, increased provision of treatment might actually lead to increases in prevalence if decreased infectiousness did not balance out decreased mortality, especially if it also led to further increases in risk behaviour, as seen in developed countries.


Wawer MJ et al. Declines in HIV prevalence in Uganda: not as simple as ABC. Twelfth Conference on Retroviruses and Opportunistic Infections, Boston, abstract 27LB, 2005.