By Imogen Foulkes
BBC News, Geneva
Weak health care systems mean universal testing is not realistic
Universal testing for HIV, followed by immediate treatment could cut the number of people developing full-blown Aids by up to 95%, a Lancet study says.
The World Health Organization (WHO) also found that such a strategy could virtually eliminate HIV transmission.
The study used computer modelling to project what would happen if everyone over 15 was tested every year.
But the WHO said that weak health care systems meant that universal testing was not a realistic idea.
At first sight, the results of the WHO study are a clear argument for universal HIV testing - it could become a run-of-the-mill medical check like those for high blood pressure or cholesterol.
Diagnosis and immediate treatment with anti-retroviral drugs could, researchers say, reduce cases of Aids in a generalised epidemic from 20 in 1,000 people to just one in 1,000 within 10 years.
Furthermore, the study continues, the strategy could virtually eliminate HIV transmission and new infection.
At the moment HIV testing and treatment are patchy, and while around three million people are receiving anti-retrovirals, a further 6.7 million need them.
But the WHO, while welcoming the study, warns that the feasibility of universal testing is challenged by weak health systems.
It adds that giving treatment to patients who are not yet sick may increase drug resistance, while the side effects of taking Aids treatment drugs for very long periods are as yet unknown but could be severe.
Writing in a commentary piece in The Lancet, Dr Geoffrey Garnett, from Imperial College London, said: "At its best, the strategy would prevent morbidity and mortality for the population, both through better treatment of the individual and reduced spread of HIV.
"At its worst, the strategy will involve over-testing, over-treatment, side effects, resistance, and potentially reduced autonomy of the individual in their choices of care."