Gonorrhoea is fast becoming 'untreatable', the World Health Organization has warned.
Antibiotics were found to have no effect on some strains of the sexually-transmitted disease.
At least three people - in Japan, Spain and France - were found to be infected with the untreatable strain, which they may have spread to others.
An estimated 78 million people contract the STI, which can cause infertility, each year.
Oral sex and a decline in condom use has been blamed for helping the disease to spread.
Dr Teodora Wi, from WHO, said: "Gonorrhoea is a very smart bug.
"Every time you introduce a new class of antibiotics to treat gonorrhoea, the bug becomes resistant.
"It will only be a matter of years and this antibiotic will not be useful anymore.
"It takes years to develop new drugs so we need to have that new drug in the pipeline so that in a few years' time, we have something to replace the current treatment.
"Worryingly, the vast majority of infections are in poor countries where resistance is harder to detect - these cases may just be the tip of the iceberg."
- What is gonorrhoea?
The infection is caused by a bacteria and spread through unprotected sex, including oral sex.
The disease can often have no symptoms and remain undiagnosed and untreated.
But those who do have symptoms could have a thick green or yellow discharge, lower abdominal pain, pain when urinating and bleeding between periods.
The infection can cause infertility and also be passed from a pregnant woman to her baby.
If left untreated, it can cause permanent blindness in newborns.
Gonorrhoea can easily be diagnosed by testing a swab sample from the genitals. Testing urine can also be used to diagnose the condition in men.
You can find your nearest sexual health clinic by entering your area of postcode here