Gonorrhoea could become untreatable, England's chief medical officer has reportedly warned.
Dame Sally Davies has written to all GPs and pharmacies to ensure they are prescribing the correct drugs after the rise of a highly drug-resistant strain of the infection in Leeds, according to the BBC.
At least 16 cases were detected in northern England this year, including 12 in Leeds where the mutated strand was first recorded, Public Health England (PHE) said in September.
The strain, which is resistant to first-line antibiotic azithromycin, was first reported in Leeds in March but spread, with cases reported in patients from Macclesfield, Oldham and Scunthorpe.
In her letter, the BBC reported that the chief medical officer said: "Gonorrhoea is at risk of becoming an untreatable disease due to the continuing emergence of antimicrobial resistance."
The letter, which the broadcaster said is also signed by chief pharmaceutical officer Dr Keith Ridge, added: "Gonorrhoea has rapidly acquired resistance to new antibiotics, leaving few alternatives to the current recommendations.
"It is therefore extremely important that suboptimal treatment does not occur."
There were almost 35,000 cases of gonorrhoea reported in England last year and it is the second most common bacterial sexually transmitted infection in the UK after chlamydia, with the majority of cases affecting people under the age of 25.
Infected patients may experience discharge or pain while urinating, but around 10% of men and almost half of women do not suffer any symptoms.
If untreated, gonorrhoea can result in severe complications and lead to infertility or septicaemia in rare cases.
Concerns have been growing over ''untreatable'' strains of gonorrhoea, and in 2012, the European Centre for Disease Prevention and Control warned that drug-resistant forms of the STI were spreading across Europe.
Dr Andrew Lee, consultant in communicable disease control at Public Health England, said: "Investigations are on-going into a number of cases of anti-microbial resistant gonorrhoea, these are seen from time to time around the country and those affected have been effectively treated with alternative antibiotics.
"We know that the bacterium that cause gonorrhoea can mutate and develop new resistance, so we cannot afford to be complacent.
"Individuals can significantly reduce their risk of any STI by using condoms with all new and casual partners and getting tested regularly.
"Public Health England will continue to monitor, and act on, the spread of antimicrobial resistance and potential gonorrhoea treatment failures, to make sure they are identified and managed promptly."
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