Gonorrhea has never been a pleasant disease. But now experts are growing worried -- very worried –- that strains of the sexually transmitted infection are becoming stronger, raising the possibility that super-resistant strains are taking hold.

In Britain, health officials reported this week that the number of gonorrhea cases have soared 25 per cent in the past year, in part because "superbug" strains are resisting treatment.

The UK Health Protection Agency says nearly 21,000 cases were diagnosed in 2011, with more than a third in people who had had gonorrhea before.

"We are seriously concerned about continuing high levels of gonorrhea transmission and repeat infection," Gwenda Hughes, the HPA's head of STI surveillance said in a statement.

Here in Canada, researchers reported in January that the last oral antibiotic used to treat gonorrhoea, called cefixime, is beginning to fail to cure the infection.

The finding wasn't altogether surprising; a strain of gonorrhea that's less susceptible to cefixime has been making its way around the globe for some time now. But until this study, it wasn’t clear if drug-resistant gonorrhea was a problem in North America.

The study found, in about seven per cent of gonorrhea cases treated at a Toronto clinic, cefixime failed to cure the infection. In many of those cases, the patients had to be treated a second time either with an injectable antibiotic called ceftriaxone, or a double dose of cefixime. Many other patients simply didn't return to the clinic for follow-up, so it's unclear if there might have been even more cases that weren't fully treated.

The study’s lead author, Dr. Vanessa Allen of Public Health Ontario, notes that patients whose gonorrhea cases are not fully treated typically don't realize it. That means they could go on to infect others with their resistant strain, thereby worsening the problem.

"That is really the largest concern," she tells CTV News. "We need to make sure when individuals are treated that the infection no longer returns and we can rely on it being gone."

It's a problem being seen all over the world. In Europe, drug-resistant gonorrhea accounted for almost one in 10 cases of the disease in 2010 -- more than double the rate of the year before, officials from the European Centre for Disease Prevention and Control said last June.

Left untreated in women, gonorrhea can cause scarring of the fallopian tubes, infertility and stillbirths.

It can also cause infertility in infected men, though typically, infected people have no symptoms.

Not very long ago, the infection was treated easily with antibiotics. But gonorrhea bacteria can mutate quickly and have "learned" how to resist the drugs. In the 70 years that antibiotics have been used to treat the infections, the bacteria have learned to resist class after class of antibiotics.

The main reason for the drug resistance, say doctors, is the overuse of antibiotics and patients who aren’t completing the full course of treatment -- both of which lead to genetic mutations within the bacteria.

Allen worries what might happen if drug resistance is not brought under control.

"The concern is not only for the individual, that they may not be able to be treated effectively, but I think there is a very real concern that the overall rates of gonorrhea would increase, both in terms of numbers, and in terms of severity of disease," she says.

Some countries are now asking doctors to change the way they treat the infection.

The U.S. Centers for Disease Control, for example, recently changed its recommendations, advising doctors to treat with injectable ceftriaxone in combination with either azithromycin or doxycycline, both of which are oral antibiotics.

Public health advocates are also stepping up efforts to remind people who are sexually active that they can help to control the spread of gonorrhea and other sexually transmitted infections by consistently using condoms.

Jane Greer, who works at the Hassle Free Clinic in Toronto, which provides sexual and reproductive health services, says she wasn’t surprised by the Canadian study findings because staff at the clinic had already been noticing patients who were being treated for gonorrhoea but still testing positive a few weeks later.

She says it’s alarming that the infection is resisting yet another form of antibiotic, since it could mean that the bacteria will soon learn how to resist the injectable drugs too.

"It is not a matter of if the new treatment – the injection -- will fail, but a matter of when," she says. "And if we are looking at other countries, they are already experiencing this and are having to treat gonorrhea with IV treatment. And if that fails, we don’t know what is coming after," she says.

Dr. Allen says there are currently no commercially available antibiotics after this class of antibiotics that are approved for the treatment of gonorrhea.

"We really need solutions as fast as possible. It is a race against time," says Dr. Allen.

Greer agrees.

"The worst-case scenario is ultimately it becomes completely untreatable. And that is a nightmare scenario," she says.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip