Matthew Sachs, 29, is a graduate student in San Francisco who is HIV-negative. He lists his PrEP status on social media. (Nick Otto for The Washington Post)

On online dating sites, Matthew Sachs identifies himself as a 5-foot-8, 130-pound grad student who likes hiking, performance art and community service. He says he’s interested in meeting a broad range of guys, from jocks to geeks, and notes that — oh, by the way — he’s “On PrEP.”

Those four letters stand for a daily medical regimen in which healthy individuals take a blue oval pill to lower their risk of becoming infected with HIV. The treatment, known as pre-exposure prophylaxis, has become so common in the Bay Area’s gay community that it’s frequently mentioned in social media profiles from Facebook to Scruff.

Since the first breakthrough research was published in the New England Journal of Medicine in 2010, the once-a-day dose of Truvada has consistently been shown to reduce the risk of HIV infection by as much as 90 percent. The results of the most recent study, which was published in September, were even more encouraging: Not one of the 600 people taking the drug became infected over two years.

As many as 10,000 San Franciscans could now be on PrEP, according to one city official’s estimate. The treatment has been transformative here, not just in medical terms but in how it has changed the nature of dating, love and relationships between those who are HIV-positive and those who aren’t. And it has prompted some AIDS experts to consider something that would have been unfathomable during the dark days of the 1980s: Could the nation’s onetime epicenter of HIV/AIDS be the place where the epidemic that has so haunted Americans begins to come to an end?

Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, is one of the believers. It’s “very realistic,” he said, that San Francisco might see new HIV infections cease in several years. But the rest of the country will be more challenging, he said.

“We have all the scientifically proven tools to end the epidemic,” Fauci said. “We now need to get politicians, medical care providers down to individual community members on board to use them right and use them aggressively.”

San Francisco physician Stephanie Cohen, who is part of a city team focusing on HIV, said local leaders have set this goal: no new infections, no AIDS-related deaths and no HIV-related stigma by 2020. “Things are looking very positive,” she said.

Of the estimated 1.2 million Americans who could benefit from PrEP, 25,000 to 60,000 people are on it, according to the Centers for Disease Control and Prevention. In 2015, the agency launched a campaign to target individuals who are at substantial or high risk and get them on the medication. The response has been underwhelming.

Fears of the drug’s possible side effects are hampering such efforts, as is the stigma of being a “Truvada whore” associated with HIV or risky behaviors, public health officials say. There are also the lingering worries, expressed most vocally by Michael Weinstein of the Los Angeles-based AIDS Healthcare Foundation, that PrEP could backfire. The internationally known activist said that he is troubled that some people are using it as a “party drug,” not taking it regularly or buying it on the black market as a way to justify not using condoms — which makes the spread of other sexually transmitted diseases more likely.

“There are mixed messages in the way this is being promoted,” Weinstein said. “It’s a dangerous game. HIV is a killer STD we didn’t know about 40 years ago. What’s looming on the horizon if we continue down this road?”

CDC Director Tom Frieden explains how pre-exposure prophylaxis, or "PrEP," could help in the fight against HIV and AIDs. (Centers for Disease Control and Prevention)

San Francisco has long been a leader in the AIDS epidemic. Randy Shilts’s 1987 bestseller “And the Band Played On” described the city’s fear and grief as the disease erupted, claiming hundreds and then thousands of lives. And as new drugs turned HIV from a death sentence into a chronic disease, San Francisco has been out front in trying different approaches to counter transmission.

Two years ago, city Supervisor Scott Wiener “came out of the PrEP closet,” as local media put it, by announcing he was on the medication. His fellow supervisors vowed to figure out a way to make San Francisco the first place in the country where anyone who wants the therapy can have access to it for little or no charge.

That vision is moving closer to reality.

On a recent morning in the Castro district, the line outside the community health center — called Strut and operated by the San Francisco AIDS Foundation — was 30 people long despite the fact that it wouldn’t open for another half-hour. Inside was one of the nation’s first clinics dedicated to PrEP.

Strut’s goal is to assess a person’s eligibility for Truvada, run all the necessary medical tests, explain how the drug is taken and the possible side effects, and figure out a way to minimize the $13,000-a-year retail cost — all within 90 minutes. The state’s Medicaid program covers PrEP, as do most insurance plans. The drug’s manufacturer, Gilead Sciences, offers a generous discount card that helps offset co-pays.

Pioneered by Steve Gibson and Pierre-Cédric Crouch, both longtime HIV/AIDS health advocates, the clinic opened just over a year ago and aims to overcome many of the barriers that have caused efforts elsewhere to falter. It already has signed up more than 700 men, ages 18 to 71, all by word of mouth.

Gibson, the clinic’s director of sexual health, explained that when Truvada was first approved by the Food and Drug Administration in 2012, the medical community thought it was something that would be prescribed by a primary care doctor and that it would cause stampedes at drugstores.

But it turned out that many physicians didn’t feel comfortable giving healthy individuals the heavy-duty drug — a combination of emtricitabine and tenofovir, which are used to treat AIDS. Many doctors also were reluctant to have the explicit sexual discussion typically required.

Strut’s program involves a team of four nurse practitioners working with four benefits navigators who are skilled in making sure their clients — technically not patients since they’re not sick — get the drug free or as close to free as possible.

Clients run the gamut: men with HIV-positive partners; men interested in a relationship with someone who is infected; men concerned about their wellness who want to be as proactive as possible.

A 29-year-old named Jil had come in that Monday morning because of peer pressure. His boyfriend and other friends are on the treatment, he said, and they had persuaded him to start it not only for his own health but also for that of the community.

“At the beginning, when it first came out, I thought it was weird to be on it,” said Jil, who asked that his last name be withheld. “Now I think it’s odd if someone says they aren’t on PrEP or don’t plan to be.”

For Crouch, the director of nursing, as for other staffers at Strut, the most striking change is how the community is evolving because of PrEP — with so many HIV-negative men who are on the regimen and so many HIV-positive men in treatment that keeps their virus levels too low to pose a risk to others. “There was always an unspoken rule that there were two tribes: HIV-positive and HIV-negative, and only some people would cross those lines,” he said. “Now we are seeing HIV status becoming irrelevant.”

The city’s efforts have not been without challenges. Despite the HIV team’s work, Cohen said it has been hard to sign up transgender women, IV drug users and heterosexual residents who are at risk. A few insurers have asked people to sign waivers saying they pledge to use condoms during sex. That makes Gibson bristle. “Frankly, it’s inappropriate,” he said.

Still, San Francisco keeps making progress.

Sachs was an early adopter of PrEP, starting the pill at 27. Even two years ago, people often hid the fact they were on the regimen, he said. Now there’s growing ease in discussing it openly. He said he has received a lot of online inquiries from strangers about his PrEP status and that nearly three-quarters of those wanted more information about the drug.

He tells them that one of the biggest benefits for him has been psychological. Before he started, the specter of HIV was always on his mind. An uncle died a difficult death from AIDS-related complications, and his family worried that the same thing would happen to him.

“Before I was on PrEP, I was terrified,” Sachs said. Now, he feels more free to meet people and have honest and open conversations about HIV. It’s the same change that he says is taking place throughout the city.

San Francisco is “becoming free of the stigma and fear,” he said. “We still have a long way to go before it’s truly eliminated, but it’s been amazing seeing the transformation over the past few years.”