A new smartphone application is fanning a syphilis epidemic outbreak among Canterbury's young gay men, a doctor says.

Christchurch Sexual Health Clinic senior clinician Heather Young said gay men would usually contract syphilis after meeting at venues such as clubs, saunas or brothels but this year there had been an increase in men meeting electronically.

"In 2011, sex-on-site venues were associated with 50 per cent of syphilis cases but in 2012 it is more commonly found after use of internet dating sites or the Grindr app," she said.

Grindr is a free social networking app for gay men. The app uses GPS to notify members when there is another gay man nearby.

Young said gay men needed to be aware of the outbreak and should "take responsibility" by ensuring they were tested.

"People think syphilis is an old infection that is not associated with the modern day but it is re-emerging globally," she said.

Christchurch homosexual Dixie McGregor said Grindr was "the new and popular" way to meet other gay men.

McGregor, who does not have the app, did not think it was responsible for the rise in syphilis cases: "It's just the new thing at the moment but no matter how you meet someone it's still up to the individual to make sure they are having safe sex."

Canterbury District Health Board clinical director of sexual health Ed Coughlan said the syphilis epidemic had got worse in recent months.

"It's difficult to say why it's increased recently but once it's in the community, among the men who have sex with men population, it's just very infectious, so it's just spreading."

He said the average age of people contracting the sexually transmitted disease had dropped from 46 to 24, with men as young as 19 being affected.

Coughlan said there were eight reported cases in 2011. So far this year there had been 22.

"If it carries on this way we'll be looking at a fourfold increase and that's quite concerning," he said.

"Some people have reported having female sexual partners, so of course that poses another risk but this year it has been only men who have been affected in Canterbury."

An Environmental Science and Research report showed there was 83 syphilis cases reported last year in New Zealand.

Syphilis facts

The disease is passed through direct contact with a syphilis sore.

Early-stage symptoms include mouth and genital ulcers, hair loss and rashes.

In its early stages, the disease is easily treated with a penicillin injection.

Late stages of the disease can cause paralysis, blindness, dementia or premature death.