There used to be a bar in Boys’ Town, where most of Chicago’s gay bars are clustered, called Christopher Street. It was a small place, with risers on one side where the best-looking guys used to array themselves, like so much merchandise.

I was 16 years old in the summer of 1981 and I would sneak into Christopher Street with my gay friends. (I had gay friends and straight friends then, the latter kept in the dark about the former.)

My gay friends called me frigid because I wouldn’t pick up tricks or go to the baths or suck off guys in the gay porn shop down the street from the bars. I called them sluts because they would. I wanted a boyfriend, I told my friends, not VD. They told me venereal diseases were nothing to worry about—go to the clinic, get a shot, head back to the bars.

“We get a lot of shit for being gay,” my friend David liked to say. “We deserve a lot of sex.”

I was with David—tall, copper-haired, beautiful, and not interested in men under 30—at Christopher Street when I first heard someone mention something called GRID, or “gay-related immune deficiency.” It was late 1981 and gay men in New York City and San Francisco were coming down with rare cancers and strange infections. It seemed to be some sort of new sexually transmitted disease, something that a trip to the VD clinic and a shot in the ass might not clear up. Or maybe it was drugs. Or poppers. Or a government plot to ruin our lives.

But we didn’t have to worry about it because we didn’t live in New York City or San Francisco, which is where the disease or the bad drugs or toxic poppers or government plotters were.

One year later that disease got a new name, AIDS, and suddenly we were all worried. Three years later David was dead.

So what do you need to know about 1981?

That given the right environment, a new sexually transmitted infection can emerge and kill thousands, hundreds of thousands, millions. That we can never go back to the kind of rampant promiscuity that characterized the ’70s and early ’80s—even if we one day have a vaccine or a cure for AIDS—because it happened once and it could happen again.