Gonorrhea, the second most commonly reported sexually transmitted disease in the United States, is becoming increasingly resistant to all standard antibiotic treatments currently available, and the Centers for Disease Control and Prevention warns that unless action is taken, there may be no way to treat this STD that infects more than 600,000 people annually.

"It is time to sound the alarm," director of STD prevention at the CDC Dr. Gail Bolan, wrote in a commentary in the New England Journal of Medicine on Feb. 9. "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."

Antibiotic-resistant gonorrhea emerged during World War II when it became resistant to sulfanilamide, then to penicillins and tetracyclines in the 1980s, and by 2007 it developed resistance to fluoroquinolones. The CDC said that gonorrhea treatment options are limited to third-generation cephalosporins that are taken with one of two other oral antibiotics (either azithromycin or doxycycline).

However, researchers from the CDC's Gonococcal Isolate Surveillance Project saw a 17-fold increase in the minimum inhibitory concentrations (MICs), which measures the drug susceptibility.

“MICs for oral cefixime went from 0.1 percent in 2006 to 1.7 percent in the first six months of 2011,” Bolan wrote meaning that the bacteria’s resistance to this last line of defense is increasing rapidly.

Researchers noted that although the MIC breakpoints for resistance to cephalosporin have not been defined, the Clinical and Laboratory Standards Institute defines susceptibility to cefixime and ceftriaxone as MICs of 0.25 μg per milliliter or below.

In the past when the Gonococcal Isolate Surveillance Project identified an antimicrobial resistance prevalence of more than 5 percent, national treatment recommendations were changed to focus on other effective drugs, but currently there are no other treatments.

"The point now 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," Bolan wrote in the NEJM. "We have the potential of having no other antibiotics to turn to.”

Cephalosporin-resistant strains have already been identified in Japan and the U.K., and while the drugs are still effective against most strains in the United States researchers stress that investment in rebuilding treatment defenses against gonococcal infections now is imperative to public health.

“If history is any guide, however, such strains will continue to evolve. Indeed, we should anticipate the emergence of fit cephalosporin-resistant strains that can spread widely,” Bolan wrote and stressed that patient vigilance and coordinated public health policies are critical for the U.S. to avoid the spread of cephalosporin-resistant strains.

Some possible symptoms of gonorrhea are vaginal discharge, lower abdominal pain or pain during intercourse in women, and men can also experience burning sensation during urination. Untreated infections can develop into serious health issue like pelvic inflammatory disease, which can lead to infertility in women.

The STD is spread through vaginal, anal or oral intercourse and can be transmitted during childbirth, and according to the CDC sexual abstinence is the only 100 percent effect method of gonorrhea prevention, although proper use of latex condom and intercourse with an uninfected person will dramatically reduce the risk.

Researchers said that it is important more people to undergo routine medical examinations because people infected with gonorrhea often do not exhibit symptoms.

"Though there is no evidence yet of treatment failures in the United States, trends in decreased susceptibility coupled with a history of emerging resistance and reported treatment failures in other countries point to a likelihood of failures on the horizon and a need for urgent action, "said co-author Judith Wasserheit, professor and vice chair of the Department of Global Health at the University of Washington in Seattle in a statement.