Untreatable cases of "superbug gonorrhoea" have occurred, the World Health Organization says, as it calls for new drugs to treat the bacterial infection.

On Thursday, WHO and a global team of researchers published a study in the journal PLoS Medicine highlighting increases in drug-resistant gonorrhea, calling it a "serious situation."

The United Nations health agency now advises doctors to prescribe two antibiotics called ceftriaxone and azithromycin for the sexually transmitted disease.

"We are starting to see resistance emerging to these drugs and even, as we say, superbug gonorrhea," Dr. Manica Balasegaram, director of the Global Antibiotic Research and Development Partnership, told reporters from Geneva.

Gonorrhea can infect the genitals, rectum and throat. Each year, it's estimated 78 million people become infected. Most women with the infection have no symptoms and 40 per cent of men don't either. Left untreated, men and women can become infertile and face an increased risk of HIV.

Gonorrhea on the rise

In women, it can lead to abdominal pain, pelvic inflammatory disease and ectopic pregnancy. If a pregnant woman's infection goes untreated then the newborn could be infected, leading to blindness.

In the U.S., the Centers for Disease Control and Prevention said 395,000 cases were reported in 2015, a 13 per cent increase from the year before. There was a similar rise of 15 per cent reported in Canada.

Data from 2009 to 2014 suggests:

Widespread resistance to the antibiotic ciprofloxacin (97 per cent of countries that reported data in that period found drug-resistant strains).

The emergence of resistance to the current last-resort treatment, the oral antibiotic cefixime or injectable ceftriaxone (66 per cent of countries reporting).

Superbugs, or extensively resistant strains that could not be cured with the last line of defence, have been reported in France, Japan and Spain.

Patients who disappear without follow-up

"After one of those cases, (the patient) just disappeared," said Dr. Teodora Wi, a medical officer with WHO's Department of Reproductive Health and Research from Geneva. "They don't come back for follow-up. You can infect others by having this untreatable infection. It can be transmitted."

Wi is also concerned that the resistance data, which comes from high-income countries, just represents the tip of the iceberg of cases that go undocumented in low-income countries, such as most of Africa. She said simpler and better ways to diagnose resistance are needed.

The agency also called for:

Faster development of new drugs, given that untreatable gonorrhea will have serious consequences.

Evaluations of existing antibiotics to treat resistant gonorrhea.

Easier to administer treatments, such as combination packages.

Simplified treatment guidelines.

The researchers said several factors contribute to rising resistance, including decreased condom use, increased urbanization and travel, poor detection rates and inadequate or failed treatment.

Practising safe sex, using condoms and getting tested are ways that individuals can protect themselves, said Dr. Alanna Fitzgerald-Husek, a physician on the communicable diseases team at Public Health Ontario.

Fitzgerald-Husek said she's worried about the about the growing rates of resistant gonorrhea and other infectious diseases.

"What we're seeing now in Canada is that we're coming to one of our last antibiotics that is effective," Fitzgerald-Husek said.

"It's a combined treatment of two different antibiotics that need to be taken together," Fitzgerald-Husek said. "Beyond this, we don't what happens next."

Ultimately, Wi said, a vaccine is needed, because gonorrhea will become resistant despite the efforts to stay a step ahead with antibiotics.

The findings will be presented at the STI & HIV World Congress in Rio de Janeiro, which runs from July 9-12.