Gonorrhoea is becoming drug resistant in North America, with one in 15 cases of the sexually transmitted disease reported by doctors as failing to respond to the antibiotic cefixime.
A report in the Scientific American points to a study led by Vanessa Allen, of Public Health Ontario, which studied people who were treated for gonorrhoea with cefixime at a Toronto clinic.
Those treated were required to return for a follow-up appointment between two to four weeks later to see if the course of antibiotics had been successful.
Clinicians also interviewed patients to find out if they might have been exposed to gonorrhoea, also known as the clap, since their first visit.
Of the 133 study participants, 6.77 percent (one in 15) failed to respond to treatment and still had the STD.
More than 321,000 cases of gonorrhoea in the US are reported every year. Globally, an estimated 62 million people are diagnosed with it annually.
It is easily cured but if untreated can cause serious health problems, including pelvic inflammatory disease, meningitis, septicaemia and infertility. Babies born from women with the disease are at risk of blindness.
No effective backup
Antibiotics have been used to treat gonorrhoea for half a century and while other types of medicine have become redundant as the disease evolved, concerns are mounting over what treatment could replace cefixime.
"The antibiotic pipeline is running dry," Robert Kirkcaldy, of the Division of STD Prevention at the Centre for Disease Control, said in an essay published in the Journal of the American Medical Association.
"[Drug-resistant gonorrhoea's] arrival [is] deeply troubling; clinicians now face the emergence of cephalosporin-resistant N. gonorrhoea without any well-studied, effective backup treatment options," the essay said.
As a result of the new strain, the centre has recommended that doctors prescribe sufferers with an injection of ceftriaxone as well as a week-long course of azithromycin or doxycycline antibiotics.
It said: "All patients treated for gonorrhoea should be given risk reduction counselling, offered condoms and retested for gonorrhoea three months after treatment.
"Clinicians must remain vigilant for cephalosporin treatment failures and report suspected cases to the local or state health department.
"Patients with persistent or recurrent symptoms shortly after treatment should be retested for gonorrhoea by culture."