Cases of the sexually-transmitted infection gonorrhoea jumped more than usual across the country during summer.

A large spike in rates of gonorrhoea across the country could be an unusual "blip" in the data or a sign the disease's resistance to antibiotics is increasing, an expert says.

ESR figures show the number of cases tested in sexual health clinics jumped from 253 during the last three months of 2016 to 382 during the first three months of this year. Between January and March last year that figure was 234.

In Wellington the number of gonorrhoea cases almost tripled. Sexual health clinics in the Capital and Coast District Health Board area recorded 92 cases between January and March this year, compared to 32 during the last three months of 2016 and 26 during the first three months.

Flickr Sexual health clinics recorded 234 cases of gonorrhoea during the first three months of 2016. That number jumped to 382 during the first three months of this year.

Dr Collette Bromhead, a senior lecturer in Molecular Microbiology at Massey University, said the spike was largely during summer, which was always an interesting time of year because people were more sexually active and there were more sexually transmitted infections (STIs) going around.

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Bromhead, who has a background in laboratory work, said the rise in gonorrhoea cases were predominantly in men. The data suggested men having unprotected sex with other men was behind the increase.

SUPPLIED Collette Bromhead says the rise in cases could be due to an increased resistance to antibiotics used to treat gonorrhoea.

"We have an ongoing problem with men who have sex with men not wearing condoms."

Condom fatigue - a term used to describe decreased condom use - had was an issue because most of the "dreaded" STIs, such as HIV and Hepatitis C, were now largely treatable, if not curable.

But the Ministry of Health's director of Public Health Dr Caroline McElnay said similar numbers of female and male cases suggested gonorrhoea was being spread through heterosexual sex.

JOHN NICHOLSON/STUFF The number of gonorrhoea cases in Wellington between January and March more than tripled compared to the same period last year.

Laboratory surveillance showed the increase was mainly in the larger metropolitan areas, McElnay said.

Bromhead said the big problem with treating gonorrhoea was the increasing antibiotic resistance of the bacteria.

What the data did not show was how many separate people had been recorded as having the disease.

123RF Fewer people using condoms could also be partly to blame for the increase in gonorrhoea cases.

"Sometimes people keep having symptoms ... and keep going back and getting tested, that can add to the statistics. That's what happens when you've got antibacterial resistance ... that may be what's happening here."

Sufferers could be reinfected, and the more often that happened the greater the likelihood of antibiotic resistance growing.

People needed to use condoms to avoid getting the infection, and get tested, Bromhead said.

McElnay said no resistance to Ceftriaxone - the antibiotic used to treat gonorrhoea - had been detected in New Zealand up until the end of March.

Reduced gonorrhoea susceptibility to the antibiotic was very rare, with just one case in 2015, and two recorded last year.

The antibiotic could still be used to treat the gonorrhoea in these instances, McElnay said.

In an effort to decrease rates of STIs, the ministry had worked with the New Zealand AIDS Foundation for more than 10 years to encourage condom use. A number of sexual health providers also promoted safe sex.