Four years ago the Aids epidemic in North America was declared to be all but over. Now, it is back with a vengeance.

Four years ago the Aids epidemic in North America was declared to be all but over. Now, it is back with a vengeance.

From coast to coast, doctors and public health officials are reporting an alarming surge in HIV infection caused in part, by a backlash among young gay men against the notion of safe sex. In some of America's largest cities, the increasing incidence of unprotected gay sex - particularly when combined with incautious sharing of illegal drugs - is triggering alarm bells unheard since the disease emerged in the early 1980s.

This week in San Francisco, a panel of Aids experts, reported that the rate of new HIV infections has more than doubled since 1997. Some 2.2 per cent of the uninfected gay population is projected to contract HIV this year, up from 1.04 per cent in 1997 and a huge leap after more than a decade of stable or declining figures. "We are very concerned," said Dr Willi McFarland, an epidemiologist with the San Francisco Department of Public Health. "These are sub-Saharan African levels of transmission.''

Just as San Francisco led the country into the Aids epidemic in the early 1980s, it is now believed to be a harbinger for gay communities across the United States and Canada. According to the Centers for Disease Control and Prevention in Atlanta, the main federal health agency, gay males in Los Angeles, Miami and Seattle are reporting higher incidences of anal gonorrhea - a condition that increases the risk of HIV infection up to fivefold and is seen as a reliable early warning.

In New York, another study found particular cause for concern among young black gay men. A survey of 542 gay and bisexual men found 33 per cent of blacks between the ages of 23 and 29 testing positive for HIV. In the same age group, just 2 per cent of white men were affected, and 14 per cent of Hispanics. City officials had no explanation for the disparity.

All this is a far cry from the optimism of the mid-1990s, when falling infection rates and the development of anti-retroviral drugs called protease inhibitors caused health officials and media commentators to hail what Andrew Sullivan, an expatriate British writer who is himself HIV-positive, called "the twilight of an epidemic".

The thinking then was that HIV-negative men were far less likely to become infected, and those who were positive could expect to stave off serious illness and extend the quality and length of their lives indefinitely.

What happened, however, was that the mixture of personal caution and aggressive public health intervention that brought the disease under control was relaxed to a potentially deadly degree.

Much of the faith in protease inhibitors was misplaced. Certainly, the initial effect was a dramatic slowdown in the onset of Aids. But, over time, the drugs have proved to be disconcertingly toxic, with side-effects including bone erosion, diabetes, liver and kidney problems and bizarre rearrangements of body fat deposits. Most seriously, there are signs that the HIV virus has developed resistance to the drugs, diminishing their effectiveness.

In the meantime, a generation of young gay men has grown up with little or no memory of the devastating effects of Aids. In the 1980s it was common to see painfully wasted bodies in wheelchairs on the streets of San Francisco. But for many young people now coming of age the only experience of seeing a gay man afflicted with Kaposi's sarcoma - the blotchy facial disfigurement linked to Aids - is the Tom Hanks movie Philadelphia.

Not only has the new generation grown careless about the use of condoms, there has been a full backlash against them and against the notion of safe sex. In San Francisco, private clubs have sprung up devoted to "barebacking", the term most frequently used for unprotected anal penetration.

On the fringes of the gay community, there is even a grim fascination with seeking out HIV-positive partners. Internet chat sites feature conversations between "gift-givers" (infected men seeking uninfected partners) and "bug-chasers" (the reverse). There have been instances of Russian roulette parties, at which uninfected men randomly have sex with each other and with a another , unidentified, HIV-positive partner.

According to experts, this self-destructive trend is both an act of rebellion against the safety-first philosophy of the older generation and also the result of failed public policy. Eric Clarke, an English professor at the University of Pittsburgh specialising in gay and lesbian studies, believes there has been too much emphasis on establishing stable monogamous relationships - something that is of little interest to young men first coming out - and too little on the need to take precautions with multiple partners.

The anti-retroviral drugs have not just been misunderstood by the gay community, Professor Clarke asserts; they have also led to a massive reduction in funding for anti-Aids advocacy groups and a consequent fall-off in public awareness. It certainly has not helped that the mainstream media has virtually dismissed Aids as a serious health issue in the US and come to associate it almost exclusively with Africa.

The resurgence of HIV appears to be restricted to gay men, with HIV rates among intravenous drug users dropping by 50 per cent over the past four years, and remaining stable in the heterosexual population. But drugs remain a serious danger. The rate of new HIV infection among gay men who inject drugs is twice as high as it is among those who do not, according to the San Francisco figures. And even if the drugs themselves are not causing the infection, their use can lead to a less cautious, more fatalistic attitude.

A young drug user told the San Francisco Chronicle this week : "A term you hear sometimes is 'You're going to get it anyways'. I don't agree with that. But it's out there."