The results, published in the British Medical Journal, are based on a mathematical predictive model and suggest that longer disease-free survival - up to 25 years - may be possible for between 15- 20 per cent of HIV carriers.
Few studies have followed patients for more than 10 years and results are complicated by uncertainty over the date of infection. But scientists at the Royal Free Hospital in Hampstead, north-west London, have monitored a group of 111 haemophiliacs. A date of infection with HIV from contaminated blood transfusions can be estimated accurately. They used the white blood cell count as an indicator of the health of the immune system and likelihood of disease progression in each of the men, to predict a date for the onset of Aids.
The predictions have been correct for all individuals who have developed Aids so far - 44 by the begining of 1993. The model predicts a 25 per cent chance of 20 Aids- free years after infection. The results are more speculative for 20-25 years but suggest 15- 20 per cent of those infected will still not have developed Aids by then.