U.S. researchers are warning that antibiotic-resistant gonorrhea is becoming an increasingly worrisome reality, and that action should be taken to limit the spread of the sexually-transmitted disease.

“During the past three years, the wily gonococcus has become less susceptible to our last line of antimicrobial defense, threatening our ability to cure gonorrhea,” said Dr. Gail Bolan of the Centers for Disease Control and Prevention’s division of sexually transmitted diseases prevention. “We’re trying to stay a step ahead by putting these warnings and alerts out.”

According to the CDC, gonorrhea has a long history of developing immunity to antibiotics, but there have always been stronger medicines available to treat it.

But in the Feb. 9 issue of the New England Journal of Medicine, CDC researchers said 1.7 percent of gonorrhea is now resistant to cephalosporins, drugs considered the last line of defense. And while that percentage may seem small, it represents a 17-fold increase since 2006.

“The point now,” Bolan told Health.com, “is that we are down to the last class of antibiotics that we know — that have been studied — to be effective in the treatment of gonorrhea,” adding that if a strain of resistant gonorrhea were to take hold, “we have the potential of having no other antibiotics to turn to.”

More than 600,000 Americans contract gonorrhea every year, making it the nation’s second-most common communicable disease. Symptoms include burning urination, abdominal pain, itching, and genital discharge. But since there are often no symptoms at all, “many patients who have this infection don’t know they are infected. So for individuals, it’s very important to go in for routine medicals,” Bolan emphasized.

She also stressed prevention, noting that gonorrhea can be warded off with the use of condoms.