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ATLANTA -- Federal health officials took steps Thursday to head off the emergence of a new gonorrhea "superbug" that's resistant to standard antibiotics.

Gonorrhea, a sexually transmitted disease that infects 700,000 Americans a year, already has become resistant to all but one class of antibiotics and could soon become untreatable, federal health officials warned. Doctors at the Centers for Disease Control and Prevention issued new treatment guidelines, hoping to delay the inevitable day when standard drugs no longer work. The guidelines call for withholding a potent oral antibiotic now commonly used to treat the infection. Instead, doctors should use an injectable form to which the gonorrhea bacteria seems less likely to develop resistance, along with a second type of antibiotic pills.

"Gonorrhea for years has developed resistance to every antibiotic we've thrown at it," says Kimberly Workowski, an infectious-disease expert at the Emory University School of Medicine in Atlanta.

Now, "we're at the end of the line on standard therapies," says P. Frederick Sparling, a professor of medicine at the University of North Carolina-Chapel Hill.

Gonorrhea is a major cause of infertility among women. It increases the risk that people will be infected with HIV, the virus that causes AIDS, and that they will spread it to their partners, according to the CDC.

As recently as 2007, doctors could treat gonorrhea with a class of antibiotics called fluoroquinolones, which include the drug Ciprofloxacin, or Cipro. Now, those drugs no longer work for gonorrhea. Instead, doctors have turned to a class of drugs called cephalosporins, also used to treat serious conditions such as bacterial meningitis and salmonella poisoning, says Sparling.

Yet even these antibiotics may not be useful for long, he says.

Doctors reported their first possible treatment failure in Japan in 2003 and detected a highly resistant "superbug" form of gonorrhea there in 2009. That superbug - which resisted treatment with an antibiotic called ceftriaxone - has also been detected twice in France and once in Spain, Sparling says.

While the superbug hasn't yet been detected in the USA, "it is likely a matter of time" before drug-resistant gonorrhea spreads here as well, says Susan Philip, director of STD prevention and control services at the San Francisco Department of Public Health. Doctors are already seeing the beginnings of drug resistance on the West Coast, especially in gay and bisexual men, Philip says.

In a February report in The New England Journal of Medicine, Sparling wrote that nearly 2% of gonorrhea samples showed reduced susceptibility to cefixime, an oral drug commonly used for initial treatment.

In the western USA, 4% of samples showed reduced susceptibility to cefixime; in men who have sex with men, nearly 5% showed reduced susceptibility to that drug, Sparling wrote.

Once resistance to gonorrhea develops, patients won't have good options, Sparling says. Only one new antibiotic against gonorrhea is currently is development, although researchers are also testing combinations of currently available drugs.

Patients who become infected with a resistant strain of gonorrhea would have to be treated with alternative medications that aren't proven to work and which could cause more toxic side effects, Sparling says. For now, he says, experts are advising doctors to test patients who aren't helped by current treatments, and test them for resistance. Because gonorrhea tends to be especially common among the poor, doctors typically try to treat patients with a single dose of medication on the same day they arrive at the clinic, along with treating their sexual partners, Sparling says. The CDC is now urging that initial treatment of gonorrhea be with a single injection of ceftriaxone, which still is usually effective.

In some ways, gonorrhea has always been a "canary in the coal mine," for doctors, because "it picks up resistance very easily," says Carlos del Rio, a physician on the board of directors for the Infectious Disease Society of America, and an author of the new CDC treatment guidelines. Gonorrhea became resistant to the first antimicrobial drugs used against it, as early as the 1930s. Doctors began using penicillin, one of the first antibiotics, in the 1940s. But the bacteria eventually mutated to become resistant to penicillin, too.

Doctors have been concerned about the rise of resistant strains of all kinds of bacteria for years, as antibiotics are overused both in medicine and agriculture.

Antibiotic resistance is so common that doctors now have to think carefully about the drugs they prescribe for common conditions, such as ear infections, sinus infections and urinary tract infections, says Judith O'Donnell, head of infectious diseases at Penn Presbyterian Medical Center in Philadelphia.

More ominously, doctors are now combating antibiotic-resistant tuberculosis and staph infections, says Sparling, director of the North Carolina Sexually Transmitted Diseases Cooperative Research Center.

"People are dying in hospitals with pneumonias and other diseases that we aren't able to treat anymore, because we don't have effective drugs," del Rio says.

In April, the Food and Drug Administration banned certain agricultural uses of cephalorosporins, such as to prevent disease in turkeys, chicken, cattle and pigs. The agency cited the need to make sure that cephalosporins remain potent weapons against human disease.

"We desperately need new antibiotics to fight infections," del Rio says. "The pharmaceutical industry has very little incentive to do the research and development for an antibiotic that you take for five to 10 days, though, compared to something like a cholesterol drug, that you take for the rest of you life."

Del Rio notes that the infectious disease society supports federal legislation that would provide financial incentives to drugmakers who create new antibiotics.

In the age of an incurable and often fatal disease such as AIDS, some people no longer take gonorrhea seriously.

But Philip says gonorrhea - spread through vaginal, oral and anal sex - can cause a variety of serious problems, especially in women, who often have no symptoms.

Gonorrhea increases the risk of a dangerous condition called ectopic pregnancy, when a fertilized egg implants in the fallopian tubes, rather than the uterus. It also can cause pelvic inflammatory disease, which can lead to infertility. Gonorrhea also can harm newborn children of untreated mothers, although this rarely happens in developed countries such as the USA, where women and babies receive preventive screening and care, Workowski says. People can protect themselves by being monogamous and using condoms.

The concentration of gonorrhea cases among the poor is especially evident in African Americans in the South, with infection rates 30 times higher in Mississippi than in Wyoming, according to the CDC.

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