"We can't see the end of the epidemic but it is the beginning of a new era," Dr Kevin DeCock told the world's largest annual Aids conference in Chicago yesterday.
His optimism is understandable. Dr DeCock of the Centers for Disease Control and Prevention in Atlanta was commenting on new figures which show that Aids is being successfully curbed with the three-drug combinations introduced two years ago. A diagnosis that was a death sentence has become a chronic condition compatible with a near normal life.
Figures presented at the fifth conference on retroviruses and opportunistic infections show that US deaths from Aids peaked in 1994 and 1995 and then nosed downwards in 1996. Last year the fall accelerated.
In the first half of 1997, 12,040 Americans died of Aids compared with 21,460 in the first half of 1996. Figures for the whole of 1997, only available for New York where 16 per cent of the country's Aids patients live, show an even bigger decline at 48 per cent. Both men and women and people of all races are benefiting.
The three-drug cocktails - two older Aids drugs such as AZT plus one of the newer protease inhibitors - have revolutionised Aids care.
Typically, people start on them as soon as they learn they are infected, before they get ill. The treatment drives the level of virus in the blood so low that it is undetectable and many patients remain well. It does not work for all, however, and patients have to take around 20 pills a day at precise times.
Some specialists fear that the decline may only be a lull and that deaths will rise again as the effect of the new treatments wears off. Dr Harold Jaffe of the Centers for Disease Control said: "Are we in a honeymoon period? Is there something bad on the horizon?"
The total number of Americans living with Aids is up 13 per cent to 259,000. Between 400,000 and 650,000 are estimated to be infected with HIV. With more infected people living longer and in good health, they have less reason to contact health authorities and more opportunities to pass on the virus.
In a separate development, scientists from Rockefeller University in New York reported in Nature that they have traced the origin of the disease from a genetic analysis of HIV positive blood plasma taken from an African man in 1959. The form of the virus recovered was at an early stage of its evolution.
This suggested that the single virus which founded the epidemic existed 10 to 15 years earlier, around or just after the Second World War.
The scientists warned that the rapid evolution of HIV-1 in the past 40 or 50 years heralded even greater diversification in the future, underscoring "the need for continued surveillance".