In the week in which some commentators declared that the Aids crisis in the UK was over, experts meeting in London warned against this conclusion.
Professor Roy Anderson, of Imperial College, London, told European MPs this weekend that without a dramatic breakthrough in the search for a vaccine or cure, or changes in sexual behaviour, a 'double-wave' pattern of infection was likely.
Calculations of these waves show the UK epidemic now approaching its first peak, at about 20 years into the history of the disease. It is then likely to fall in the next 10 or 15 years, but will rise again, settling at a higher level.
Professor Anderson, of the college's department of parasite epidemiology, was speaking at the first conference organised by the British All Party Parliamentary Group on Aids, held in London on Friday and yesterday. It aims to co-ordinate national public health education programmes in the EC countries and give parliamentarians an update on the likely progress of Aids in Europe.
Professor Anderson said the impact of Aids on heterosexuals would not become apparent for many years. 'Although the risk of infection for each sexual act remains extremely small, you have to look at many sexual acts over long periods of time and that a person with HIV infection is potentially infectious for nine to ten years. Heterosexual infection is certainly still on the way up.'
Aids would become endemic and a greater problem in high-risk groups, such as those who change their sexual partners or share drug needles frequently, and who do not practise safe sex. 'Multiple peaks in the incidence of Aids may appear perhaps separated by many years, as HIV infection passes from high- via medium- to low-risk groups,' he said.
There have been 7,195 cases of Aids in the UK since counting began in 1982; 62 per cent of the victims have died. Of these cases, 491 are women, and 1,401 men and women are believed to be heterosexual. About 150 new cases are reported each month, a figure that appears to have stabilised.
The number of people with HIV who have volunteered for testing, but have not yet progressed to Aids, is 19,500. Charts provided by researchers in the Netherlands, where Aids has followed similar patterns to the UK, show that the epidemic has peaked in high-risk groups. In these it will fall to about half the current rates of infection in 10 years' time. Among heterosexuals in low-risk groups, the rates will rise very slowly, reaching the settled high-risk levels perhaps 20 years later.
It is this which has led to the claims that Aids is no longer a danger. But Jonathan Mann, professor of epidemiology and director of the Harvard School of Public Health, said that denial had always been a characteristic of the epidemic around the world.
'The claims that it did not exist in heterosexuals was one of most truly bizarre events in public health this century,' he said. 'The whole history of Aids has seen a cycle of exaggeration and denial. People have always wanted to take extreme views. If you ask people to choose between believing that there is a big problem or no problem, we know which way they will to go.'
Professor Mann, former director of the World Health Organisation Aids programme, said he understood the difficulties that policymakers and health planners now faced. 'We have to have a lot of sympathy for politicians over this question of heterosexual transmission. What is clear is that much is still unknown about how far and how fast it will spread. We might not have these answers for 20 years. We are therefore asking politicians to make decisons today that in reality they will not have to deal with in the future.
'We can only emphasise that there will be more infection, that there is risk, and that we have a duty to protect society.'
Part of the current debate in Britain has focused on the early projections of the scale of Aids infection. The first, made before 1988, were one-and-a-half times too high. As a result Aids activitists have been accused of scaremongering. However, by 1990 projections had been adjusted downwards and are close to actual numbers today.
Professor Anderson, who was responsible for the first and subsequent projections, said: 'People may wonder why such major concern is given to a disease that kills fewer people than cancer or smoking-related illnesses or car accidents.
'The first reason is its lethality. Once diagnosed, life expectancy is about 18 months. The second is that this is a new disease and very silent one. It stays in the body for a long period.'
While Professor Anderson confirmed that the numbers of infected heterosexuals was still small, he said that the spread of Aids was very slow in low-risk groups. There were too many unknown aspects of heterosexual transmission for it to be safe for people to drop their guard, he said.
While 'seed' cases among heterosexuals in Europe may have been infected abroad, they had the potential to cause the next level of infection. In France, where the heterosexual spread in greater than in Britain, this was already emerging.
The conference also heard warnings of 'sex tourism' moving from countries such as Thailand to much closer to home. Dr Johannes Hallauer of the WHO Global Aids Programme said that sex on offer in Moscow, Prague and Budapest was providing a new threat, from prostitutes with Aids spreading the disease from 'inner' Europe to the West.
There is now confidence among British Aids experts that the strong public health messages of the mid-Eighties were effective in helping to change behaviour. The rates of infection did not fulfil the blackest predictions.
But there are now concerns that schoolchildren believe that the Aids risk is all over. Peter Glover of Acet (Aids Concern, Education and Training), an independent group that offers Aids education in schools, said that children were getting these messages.
'Aids will not have the major impact in Britain that it is having overseas, but it is absurd to believe it will leave Britain unaffected,' he said. 'The threat to the heterosexual community is a real one. We must not lose sight of the fact that the major impact of Aids, everywhere, still lies ahead.'