First, it was the Centers for Disease Control—now, the World Health Organization is warning that Gonorrhea could join herpes and HIV/AIDS as "uncurable" sexually-transmitted diseases.

"We're sitting on the edge of a worldwide crisis," says Manjula Lusti-Narasimhan, of WHO's department of reproductive health and research. "There's a general complacency around sexually transmitted infections in general, and this doesn't have the same political or social pressure as HIV. That's because gonorrhea has been so easily curable so far, but in the future, that won't be the case."

Gonorrhea is estimated to infect more than 100 million people worldwide each year and can cause infertility, ectopic pregnancy, painful urination, and severe eye infections to babies born to women infected with the disease.

So far, drug-resistant strains of gonorrhea have shown up in the United States, Norway, Sweden, Austria, the United Kingdom and other countries.

All of those cases were cured with cephalosporins, an antibiotic that doctors say is the "last line of defense" against gonorrhea before moving on to injectable antibiotics. Last year, there was one published case of a strain of gonorrhea that showed resistance to injectable antibiotics as well. Lusti-Narasimhan says those cases will soon be the norm.

In February, the CDC estimated that about 1.7 percent of gonorrhea samples (taken from men with gonorrhea at STD clinics in 30 U.S. cities) was resistant to cephalosporins, a 17-fold increase since 2006.

"If [gonorrhea] didn't cause so much trouble, it'd be a really fascinating organism to study—it's a superbug, a really smart organism," she says. "It not only develops resistance rapidly, but it retains memory of past resistance, so you can't say 'Let's try out penicillin' because [the bacteria] has a memory for it."

The bacteria's penchant for building up resistance has put drug companies in a tough place—developing a new antibiotic is expensive and unlikely to be profitable, and within a few years, gonorrhea would likely develop a resistance to any new drugs used on it, she says.

"Drug manufacturers are in a bizarre scenario—why would they spend a ton of money developing a new drug for what was, until now, one of the most easily treatable STI's?" she says. "They know if they do develop a new drug, it's going to rapidly develop resistance."

So far, every case of gonorrhea in the United States has been treatable through some combination of antibiotics, according to the CDC. In an E-mail, CDC spokesperson Nikki Mayes says it's time for the international health community to "sound the alarm" that untreatable gonorrhea is on the way.

"The bottom line is that treatment of gonorrhea with cephalosporins remains effective [in the United States], and no cases of treatment failures have been seen in the U.S," she wrote. "But we do want people to be aware that if new treatments aren't developed, we may see untreatable gonorrhea in the future."