London: Cases of an antibiotic resistant sexually transmitted infection have been detected in London after initially being found only in the north, Public Health England (PHE) said on Sunday. Urging people to practice safe sex, the PHE gave a grim warning that if the current cases of a so-called "super gonorrhoea" become resistant to all forms of antibiotics, there is currently no new drug available and the infection could become untreatable, Xinhua news agency reported. The safe-sex call comes as an increase in antibiotic resistant cases of the super gonorrhoea continues, a further sign of the very real threat of antibiotic resistance to the ability to treat infections, said PHE. A national alert was issued in November 2014, when the first case was detected in the city of Leeds, with doctors discovering one of the main treatments had become useless against it. This total number of cases confirmed in England, between November 2014 and April 2016, has now increased to 34, but the number of men and women with the infection could well be much higher as there are often no signs a person is infected. "PHE continues to monitor and investigate gonorrhoea cases that are highly resistant to the antibiotic 'azithromycin'," said the agency.