A national alert has been triggered after a highly drug resistant version of the sexually transmitted infection (STI), gonorrhoea, was detected in West Yorkshire.

Fifteen cases have been detected by Public Health England (PHE) so far, the British Association for Sexual Health and HIV said.

Reports to PHE's sexually transmitted bacteria reference unit (STBRU) of cases of the infection being highly resistant to the azithromycin drug have previously been rare, it added.

The outbreak, which was first detected in Leeds in March, has since spread, with cases reported in patients from Macclesfield, Cheshire; Oldham and Scunthorpe.

All of the cases involve heterosexual patients, and some people have reported partners from other parts of England.

The association said: "An outbreak control team meeting has been convened and STBRU are currently performing next generation sequencing on these strains to better understand the molecular epidemiology."

What is gonorrhoea?

The disease is caused by the bacterium called Neisseria gonorrhoeae.

The infection is spread by unprotected sex.

Of those infected, about one in 10 heterosexual men and more than three-quarters of women, and men who have sex with 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.

It added: "PHE is concerned that the effectiveness of current front-line dual therapy for gonorrhoea will be threatened if this resistant strain continues to spread unchecked."

There were almost 35,000 cases of gonorrhoea reported in England last year. It is the second most common bacterial sexually transmitted infection in the UK after chlamydia.

The majority of cases affect people under the age of 25.

If you are concerned about gonorrhoea - or are worried you may have come into contact with the disease - call the sexual health teams at Princess Royal Health Centre on 01484 344311. You can also attend walk-in clinics at the centre, on Greenhead Road.