How to control the Aids epidemic

South Africa has the fastest-growing Aids epidemic in the world. At the end of 1996 some 2.5 million South Africans were infected with the HIV virus and infection is still increasing at a rate of about 1,500 per day. Even if numbers stabilise at the present level, some 400,000 South Africans, most of them young adults, will die in each of the next five to ten years from Aids and Aids-related disease. By 2005 the epidemic is expected to cost the country 1 per cent of GDP every year. To this must be added the cost of treating many more cases of tuberculosis, since HIV breaks down the immune system allowing latent TB to reactivate.

Clearly, HIV threatens to undermine many of the gains that were so painfully won in the struggle to create a new society. Must the country simply live with this catastrophe, taking care of those who will die as best it can? The outlook need not be as bleak as that. The virus is not invincible. It is possible to reduce the rate of infection — it can, in short, be managed. The term “managed” is the keyword, not “eradicated”, for attempts at eradication are often counter-productive. They encourage high-technology biomedical solutions, rather than approaches that actively involve local communities. When eradication fails, society often returns to square one, but with the additional burden that drug resistance may follow from failed eradication programmes. If disease management is sufficiently good, it may be possible to eradicate some diseases, but this should not be the primary aim.

If there is to be any hope of successful management of HIV, it is vital to understand the factors that increase the risk of infection and the magnitude of the epidemic. Two critical factors that increase the risk of infection are labour migration and the presence of high rates of other sexually transmitted diseases (STDs). HIV took hold in South Africa about a decade after the epidemic began to spread in the countries of East and Central Africa, in particular Uganda. The rapid geographical spread of the disease is a direct consequence of migrant labour combined with efficient transport that ensures that workers are able to move rapidly over long distances. The virus probably entered South Africa from countries to the north through the trucking routes that end in Durban and this is reflected in the provincial rates. Thus at the end of 1997 the worst affected provinces were KwaZulu-Natal and Mpumalanga, where 27 and 22 per cent respectively of women attending antenatal clinics were HIV-positive. These were followed by Gauteng, the Free State, the Eastern Cape and the North West Province with rates of 12-19 per cent, the Northern Cape and the Northern Province at 8 per cent and finally the Western Cape at 6 per cent.

Many of these migrant workers are driven by rural poverty to take jobs in the South African mines. They live without wives or families for most of their working lives, housed in single-sex hostels far removed from their rural homes and working in dangerous and stressful conditions. At the Epidemiology Research Unit, which studies the diseases of the half-a-million mineworkers in South Africa, we have talked at length to miners about their living and working conditions, and their knowledge of and attitudes to disease. The results are both fascinating and devastating. It is clear that the conditions of miners’ lives are almost perfectly designed to spread HIV both at the mines and in their rural homes.

Miners live in daily fear of accidents, and many have witnessed friends or co-workers killed or injured. They perceive HIV as just one of many risks a man faces, and far less immediate in its consequences than many others. They are supported by a macho culture through long hours of physically taxing labour in heat, humidity and confined spaces, and at the end of the day drinking and commercial sex are the two most available diversions. Large numbers of impoverished women flock to the mines from rural areas, at best to find a boyfriend who will support them and their children, at worst to make their living selling sex. Interviews with sex workers, who may have up to 30 sexual contacts a month, revealed that many had never used a condom in their lives despite fears of Aids, because their customers were unwilling to pay for protected sex.

The rate of infection has increased rapidly and this is clearly illustrated by testing of pregnant women. In 1990 less than 1 per cent of women attending antenatal clinics was infected; since then the figure has doubled every one to two years, bringing it to 16 per cent at the end of 1997. This rapid rate of increase is directly related to the high rates of other sexually transmitted diseases in the population — several studies show that 30 per cent of adults in urban communities are infected with syphilis, gonorrhoea or chlamydia. A patient with one of these diseases, involving ulcerations or discharges, is five to 20 times more likely to acquire HIV infection than someone who is free of them.

To determine the magnitude of an epidemic, social scientists have devel-oped a measurement known as the basic case reproduction number or R0. While the name is awkward, the concept is simple: R0 is the number of secondary cases that arise from a single primary case of infection. If one person has measles and infects ten other people directly, then R0 is 10. The importance of R0 is simply that if transmission can be reduced by this amount the disease will decline and eventually die out. The World Health Organization succesfully eradicated smallpox by reducing its R0 from three to nought through an extensive international programme and maintaining this reduction for long enough to free the world of this disease entirely. One reason we may continue to live with malaria for a long time to come is that R0 for malaria is about 60.

Throughout Africa HIV infection doubles in about one year. This means that, on average, each person infected with HIV infects one other person a year. If a person lives on average for seven years after becoming infected, he or she will infect seven other people before dying. So R0 for HIV is about seven. If transmission can be reduced by seven times, therefore, the epidemic will go into decline.

Rates of transmission are undoubtedly affected by patterns of sexual behaviour. The critical question is not how frequently people have sex, but how many partners they have. Sexual contact between different age groups also contributes to the spread of Aids, for new generations of uninfected young people will remain uninfected if they confine their sexual activity to their peers.

To achieve a decline in the epidemic, the first, short-term, strategy should be to reduce the incidence of other sexually transmitted diseases (STDs). If 25 per cent of the population are infected with another STD and if these increase the risk of infection by ten times, say, then eliminating them will reduce overall transmission by about three times. Most of these STDs can be treated quickly, effectively and relatively cheaply with antibiotics. If they were eliminated, R0 would fall to about two. This is over-optimistic, of course, but even halving their prevalence would have a major impact on the spread of Aids.

The second, medium-term, strategy is to persuade people to use condoms. Changing behaviour is notor-iously difficult but it has been achieved in other countries and contexts. If half the population used con-doms all the time, or if everyone used con-doms half the time, then we would have a further reduction in R0 by a factor of two and we would have achieved our goal. The third, longer-term, strategy involves addressing the issues of migrant labour and poverty that lead to social conditions in which HIV flourishes. This is even more challenging than changing behaviour, but such problems must surely be central to the new South Africa. If we cannot deal with them, our hope for the future is greatly diminished.