LONDON - A man in Britain has contracted what has been described as the world's "worst-ever" case of super-gonorrhoea.

According to the BBC, the man picked up the superbug after a sexual encounter with a woman in South-east Asia earlier this year. He also had a regular partner in Britain.

Doctors have become increasingly worried about diseases showing resistance to treatment with antibiotics.

Public Health England said it is the first known example of a gonorrhoea infection that cannot be cured with first choice antibiotics.

Health officials are now tracing any other sexual partners of the man, who has not been identified, in an attempt to contain the infection's spread, BBC said.

The main antibiotic treatment - a combination of azithromycin and ceftriaxone - has failed to treat the disease.

"This is the first time a case has displayed such high-level resistance to both of these drugs and to most other commonly used antibiotics," the BBC quoted Dr Gwenda Hughes, from Public Health England, as saying.

Discussions with the World Health Organization and the European Centres for Disease Control agreed this was a world first, BBC said.

The disease is caused by the bacterium Neisseria gonorrhoeae and is spread by unprotected vaginal, oral and anal sex.

Of those infected, about one in 10 heterosexual men and more than three-quarters of women, and gay men, have no easily recognisable symptoms.

But symptoms can include a thick green or yellow discharge from sexual organs, pain when urinating and bleeding between periods.

Untreated infection can lead to infertility, pelvic inflammatory disease and can be passed on to a child during pregnancy.

Analysis of the man's infection suggests one last antibiotic could work. He is being treated and doctors will see if it has been successful next month, BBC said, adding no other cases - including in the British partner - have been discovered, but the investigation was still under way.