The clinical director of the Wellington Sexual Health Service, Jane MacDonald, said all sexually transmitted diseases were on the rise, but the sudden explosion in the number of infectious syphilis cases was "particularly worrying".
"In the last two years in Auckland and Wellington, we have seen four times the number of infectious syphilis cases than in the previous 20 years," she said today.
At her Wellington clinic, there were five cases within a nine-month period last year, and there were already nine cases in the first five months of this year.
A study published in the New Zealand Medical Journal in March revealed that the number of people presenting to Auckland Sexual Health Service with infectious syphilis more than doubled in a 2½ year period, with a total of 40 cases recorded between January 2002 and September 2004.
Anecdotal evidence from hospitals suggested an increase among the general population.
The study's author, sexual health physician Sunita Azariah, said the increase in syphilis incidence "is a potential serious public health issue".
However, since syphilis is not a notifiable disease (doctors are not obliged to report cases to health authorities), its actual prevalence is unknown.
The Wellington Sexual Health Service is shortly to begin a survey of all GP practices in the region to try to ascertain the spread of the disease.
Dr MacDonald said syphilis had been rarely seen in New Zealand for decades, except among New Zealanders who had had sex overseas, or in recent immigrants.
"I've been working in sexual health since 1998 and I had never seen a case of infectious syphilis until last year."
The majority of cases (74 per cent in the Auckland study) were among gay men who had casual sex, she said.
"However, we do see some women presenting with syphilis."
In the Pacific region, syphilis is endemic in the heterosexual population.
A study looking at antenatal screening in Suva in 1987 found that 14.2 per cent of Fijian women tested positive for the infection.
Dr MacDonald said the infection could cause birth defects, still births and infertility.
Syphilis is known to markedly enhance HIV transmission.
Last year there were 183 new diagnoses of HIV, compared with 154 the year before.
"The insidious thing about syphilis is that two-thirds of people infected do not show any symptoms at all," she said.
"It may be only 15 to 20 years down the track that they suffer heart attacks and strokes because of the damage to their blood vessels."
Early signs include non-painful ulcers in the mouth and genital area, rashes and swollen glands.
The disease was once known as the "Great Mimicker" because the symptoms could look like almost anything: liver problems, nerve palsies, meningitis.
Rates of other sexually transmitted infections (STIs) are also on the rise in many regions, especially among 15 to 24-year-olds.
Figures released by the Ministry of Health's STI surveillance team for the first three months of the year showed that chlamydia cases reported had increased 33.2 per cent to a total of 3993 since the same time last year.
Reported cases of gonorrhoea in the last year increased 45.6 per cent to a total of 524.
Between 53 and 71 per cent of gonorrhoea patients were aged 15-24, while up to 77 per cent of chlamydia cases were diagnosed in the same age group.
Waikato recorded small drops in diagnoses for both gonorrhoea and chlamydia since the last quarter; however, gonorrhoea rates have actually increased 70 per cent in the region overall since the same time last year.
The largest increase in chlamydia cases over the last year was in Auckland (52.8 per cent).
Bay of Plenty has the worst rates of chlamydia rates overall (286.4 per 100,000 people), 25 per cent higher than Auckland or Waikato.
In the first three months of the year there were 42 babies under one year old infected with chlamydia – most likely passed on during birth.
Around 60 per cent of pregnant women in Wellington are thought to be tested, but rates vary around the country.
Dr MacDonald said it was "shameful" that neo-natal screening for chlamydia was not yet mandatory – especially as around 12 per cent of women under 25 were exposed to chlamydia.
The infection can cause a nasty eye infection in babies, and also lead to pneumonia.
The safe sex message was "not being taken seriously", and there was evidence that people were becoming increasingly blase about condom use, she said.
"There seems to be a bit of 'condom weariness' among the gay population.
"Risk-taking is back in vogue; people are essentially playing Russian roulette with unprotected sex."
According to the most recent Gay Auckland Periodic Sex Survey, 45 per cent of participants reported never or infrequently using condoms with regular partners.
Attitudes to condom use among the heterosexual population were also lax, she said.
Among some cultures, any talk of sexual activity was taboo.
"I think rather than focusing on sexual activity, we would be better off talking about the effect on families: the fact that these infections can make women infertile."
There are free youth clinics in most regions, including two in the Wellington region, and most GPs are also funded by the Government to give free sexual health treatment for young people.