Gonorrhea is becoming increasingly resistant to a class of antibiotics known as fluoroquinolones, and theyshould no longer be used to treat the sexually transmitted disease, U.S. health officials said Thursday.

Cases of gonorrhea are on the rise in Canada and the U.S., public health officials have found.

"On the basis of the most recent evidence, CDC no longer recommends the use of fluoroquinolones for the treatment of gonococcal infections and associated conditions such as pelvic inflammatory disease," the U.S. Centers for Disease Control said in its Morbidity and Mortality Weekly Report.

"Consequently, only one class of drugs, the cephalosporins, is still recommended and available for the treatment of gonorrhea."

Gonorrhea is a bacterial infection that can be transmitted through oral, genital or anal sex with an infected person. If left untreated, the disease can cause other problems, including sterility and a greater susceptibility to HIV.

Since 1993, fluoroquinolones have provided a convenient, single-dose oral therapy to treat gonorrhea, but bacteria that resist the drugs are becoming more common and widespread. Cephalosporins must be injected and are not as readily available.

"Gonorrhea has now joined the list of other superbugs for which treatment options have become dangerously few," Dr. Henry Masur, president of the Infectious Disease Society of America, said in a release.

Options are running out for treating gonorrhea, agreed Dr. John Douglas Jr., director of the CDC's division of STD prevention, adding pharmaceutical companies have no new drugs for the bacteria in their research pipeline.

Fluoroquinolone resistance is also on the rise in Canada, although federal public health officials have not made the same recommendation as the CDC.

The Public Health Agency of Canada recommends doctors check local resistance rates and take a travel history before deciding what class of antibiotics to prescribe, said Dr. Tom Wong, director of the agency's community acquired infections division.

Resistant strains of gonorrhea appear to be moving west to east. The problem was first noticed in Asia and has since moved to Hawaii, California and British Columbia, public health officials said.

In the U.S., 38 per cent of gonorrhea cases among homosexual and bisexual men were resistant and 6.7 per cent among heterosexual men, for the first half of last year, the CDC said.

Sexually active teenagers and young adults showed the highest reported rates of infection.