Gay men are being encouraged to test regularly for sexually-transmitted disease gonorrhoea.
Recently, health experts warned that some strains of the disease are becoming immune to treatments.
Gonorrhoea is a bacterial infection that, among gay men, is passed on through unprotected anal or oral sex and can spread to the throat, rectum or penis.
If left untreated, it can cause serious health problems, as well as making it easier to pick up or pass on HIV.
In men, symptoms can include drops of white or yellowish-green discharge from the end of the penis, pain when passing urine, or discomfort in the rectum. However, some cases have no symptoms.
According to HIV and sexual health charity Terrence Higgins Trust, diagnoses in gay and bisexual men in London rose 26 per cent between 2009 and 2010.
Ben Tunstall, head of health promotion at THT, said: “The emergence of drug-resistant strains of gonorrhoea is a real concern. Using condoms during anal sex will help guard against infection, but won’t protect you completely. It’s also passed on through oral sex and, if you have it in your throat, you may not have symptoms but will still be infectious.
“With rates of the infection increasing so rapidly in London, it’s really vital that gay and bi men get themselves to the clinic for a full check-up every six months, and encourage their friends and partners to do the same.”