A strain of gonorrhea that is resistant to one of the key drugs used to treat the sexually transmitted infection has been found in Quebec. It is the first time a strain of the bacteria that is resistant to the drug ceftriaxone has been found in North America.

The finding underscores that the days of easy treatment of gonorrhea are numbered.

“Antibiotic-resistant gonorrhea is coming,” said Elizabeth Torrone, surveillance team leader in the division of sexually transmitted disease prevention at the Centers for Disease Control and Prevention.

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Ceftriaxone, an injectable antibiotic, is part of the standard treatment for gonorrhea. It is given in combination with a second antibiotic in pill form, azithromycin.

This drug combination is the last of the easy-to-administer, should-work-for-everyone antibiotic therapies available to treat gonorrhea, which has plowed its way through all the drugs in the medical armamentarium. Pharmaceutical companies are working to develop new drugs, but none is expected to hit the market soon.

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“A few years ago you would just give a pill. Now you need a shot. And with time, you’ll need some maybe more toxic shots. It’s getting harder to treat,” said Dr. Jean Longtin, head of Quebec’s public health laboratory and senior author of an article on the new case. It was published in Emerging Infectious Diseases, a journal published by the CDC.

Though this case is the first in North America, it is not the first time ceftriaxone-resistant gonorrhea has been diagnosed. It was previously spotted in Japan in 2015 and there have been a few other cases seen in Asia and Europe since.

The genetic signature of the bacteria that infected the Quebec woman had some close similarities to the Japanese case, which suggests that strain might be spreading. The woman did not travel to Asia but her most recent boyfriend had previously traveled to Thailand and China and had unprotected sex in both countries.

Public health authorities tested the man, but by the time they did, he tested negative for gonorrhea.

So far, azithromycin has been the weaker of the two links in this combination treatment; resistance to it has been rising. Longtin noted that just four years ago in Quebec, all gonorrhea strains tested were susceptible to azithromycin, but now about 20 percent are resistant to the drug.

The woman was treated with the drug combination, and in her case, the azithromycin cured her infection. But with resistance to that drug rising, that cannot be considered a given.

Untreated gonorrhea can lead to infertility and increase the risk that an infected person will contract HIV. Infants born to a woman who is infected can develop blindness as a consequence of contracting the bacteria during birth.

The number of gonorrhea infections in the U.S. has risen sharply over the past few years. There were 335,000 cases diagnosed in 2012, but by last year that number had risen to nearly 469,000, according to data from the CDC. Infection rates are rising among all ages of sexually active people.

That makes the problem of increasing resistance even more acute, said Torrone, who was not involved in the new study.

“We know there’s a lot more gonorrhea out there, which means a high probability of maybe coming into contact with a strain that has reduced susceptibility,” she told STAT.

Dr. Alan Katz, who is with Hawaii’s state board of health, has also seen evidence that the power of the current therapy for gonorrhea is eroding.

Katz and his colleagues reported last year on a cluster of cases in Hawaii where the infecting bacteria had high-level resistance to azithromycin and weakening susceptibility to ceftriaxone.

The Quebec case gives him pause.

“This worries me. It worries me because we haven’t seen the ceftriaxone decreased susceptibility at this level,” Katz said.

Everyone involved in the fight against gonorrhea knows that it’s only a matter of time before the bacteria evolve to withstand the current therapy. “Gonorrhea is a really smart bug, and it has developed resistance to most of the recommended treatments in the past,” Torrone said.

So what happens then? Treatment becomes a lot harder, experts predict. Drug doses will likely be increased — in Britain, the standard treatment already involves double the dose of ceftriaxone used in the United States, Torrone said.

The current treatment paradigm — a person who tests positive is given the drugs and rarely asked to come back for retesting to ensure they are cured — may no longer work. Testing may require trying to grow the bacteria from a sample to see if any antibiotics work against it. That’s currently only done in a small number of cases.

Scientists are also looking at older antibiotics that can be harder to take, drugs that have largely stayed on the shelf because they have unpleasant side effects. “Are we going to have to go to these really killer drugs to deal with gonorrhea?” Katz wondered.