Forms of gonorrhea that don't respond to the last line of antibiotics have rapidly spread in Great Britain, expanding the reach of drug-resistant disease.

The number of gonorrhea cases with decreased sensitivity to the front-line drug cefixime increased by nearly six times from 2004 to 2011 in England and Wales, a team from the U.K.'s Health Protection Agency reported Tuesday in The Lancet Infectious Diseases.

Drug-resistant gonorrhea is a growing trend worldwide, with cases rising in Asia, North America and Europe. Japan has even documented a superresistant strain of gonorrhea that can thwart all available drugs.

Sixty years ago, doctors had a large arsenal against gonorrhea, including penicillin, ampicillin, tetracycline and doxycycline. But one by one, each of those antibiotics stopped working. Now there are only two drugs left: cefixime, which is taken orally, and ceftriaxone, which is injected into muscle.

Last summer, evidence emerged that cefixime had stopped working against gonorrhea in the U.S. The data were so worrisome that the Centers for Disease Control and Prevention sounded the alarm and issued new guidelines for treating the sexually transmitted disease. Then in January, Canada documented the first case of cefixime-resistant gonorrhea.

Gonorrhea, aka "the clap," is the second-most-common sexually transmitted disease in the U.S., with more than 300,000 cases reported in 2011.

In the current study, epidemiologists tested drug sensitivity for more than 7,000 gonorrhea cases in England and Wales. Strains that showed signs of resisting cefixime steadily increased from 2004 to 2010, when 17 percent of cases didn't respond to normal doses of the medication. This percentage then fell to 10.8 in 2011.

The gonorrhea cases that didn't respond well to cefixime also showed resistance to ceftriaxone.

These two drugs are in the same class of antibiotics. So many scientists worry that once the bacterium conquers one of them, it will eventually knock out the other, too.

The world doesn't have any backup treatments for gonorrhea. Once this class of antibiotics is gone, we've got a big problem.

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