The meeting of the 19th International AIDS Conference in Washington this week — the first time the gathering has met in the U.S. in a generation — should hold special significance for Baltimore City. Not only has AIDS claimed far too many lives here, but much of the early work to identify the HIV virus that causes the disease was carried out in Baltimore institutions.

The results of that and subsequent research represented a triumph of medical science that has transformed AIDS from a virtual death sentence into something more like a manageable, chronic illness whose victims can live for decades after being infected.

For that reason, much of the discussion at the Washington conference will focus on treatment and prevention as the next phase of the battle against AIDS. Since the disease emerged in the early 1980s, the pandemic has killed 35 million people around the world, including 620,000 Americans. And while AIDS has devastated communities nationwide, the Baltimore region has been particularly hard hit. Our area has the fifth-highest rate of AIDS cases in the country, more than double the national average.

With the development of effective drug therapies during the last two decades, medical professionals now know how to keep AIDS patients alive much longer. But the very success of their efforts has created new challenges. Who will get treatment, how much will it cost, and who will pay? And perhaps most important of all, how can medical institutions and public health officials prevent or reduce the 50,000 new infections each year that allow the disease to spread?

During the last decade in Baltimore, AIDS has evolved from a disease primarily of intravenous drug users, who spread the virus by sharing infected needles, to one that attacks young gay and bisexual African-American men, who now represent the fastest-growing population of new infections. The city health department is aggressively targeting that community with public service messages aimed at encouraging people to be tested for HIV — studies have shown that most infected people don't know they have the virus — and to practice safe sex by consistently using condoms to avoid transmitting the virus to others.

Such efforts have been proven to work. After the city initiated a needle-exchange program for intravenous drug users a decade ago, the percentage of new AIDS cases attributed infections from dirty needles dropped from 60 percent in 2001 to 25 percent today.

The city wants to launch a similar public health campaign aimed at gay and bisexual black men, but it has had difficulty persuading the Maryland Transit Authority to allow the display of some ad posters in the city buses it operates. One poster, aimed at the underground gay "ballroom" subculture in which young gay men compete in elaborate, costumed dance contests, has been deemed inappropriate by the MTA because it's slogan — "HAVE BALLS. GET TESTED." — contains a double entendre that transit officials rejected as too risque. The poster depicts a chest-up image of a young black man wearing a leather top.

While most city bus riders might not recognize the poster's reference to gay "ballroom" culture, neither is it likely most would take offense at the slogan's elliptical way of urging young men to summon the courage to find out their HIV status. All ad campaigns depend to some degree on eye-catching, memorable images and words, and not even the transit authority is claiming the health department's poster falls into the category of materials that are sexually explicit or obscene.

It took, um, guts for the city health department to sign off on a slogan that is hip enough to actually serve its intended purpose. But city health commissioner Dr. Oxiris Barbot is convinced that getting more people tested for HIV and into treatment if they're found to be carrying the virus is the key to halting the spread of AIDS in Baltimore. She's already working with hospital emergency rooms, clinics and health-care providers to make it easier for people to find out their HIV status during routine visits, and the city-operated Charm City Circulator buses have already agreed to display the posters.

At a time when the whole world is focused on testing, treatment and prevention as the front lines of the global struggle against AIDS, Baltimore should be leading the effort to find and identify those most at risk. It shouldn't have to fight the MTA on top of the disease in order to get its message out.