An "alarming" increase in the number of cases of syphilis is being reported across the country, and the reported cases could be just the tip of the iceberg.
There has been a 45 percent jump in the number of reported cases between 2022 and 2023.
Auckland has seen the biggest rise in cases, with Waikato and Canterbury rounding out the top three cities for recorded infections.
Those aged in their 30s have experienced the biggest increase, and infectious disease and sexual health doctor Massimo Giola believes the problem is worse than the figures suggest.
"It is alarming, and unfortunately I think this is just the tip of the iceberg, so the problem out there is even bigger. First of all, because not all syphilis cases are notifiable, and ESR only records the notifiable cases, so my best guess is it's probably two to three times more syphilis around than those numbers indicate."
Dr Giola told Checkpoint it was also concerning that there have been no cases reported in different areas around New Zealand, including South Canterbury, Tai Rāwhiti and Whanganui.
"So that really only shows me that there is not enough testing going around in those areas, and so yes, I think there is more syphilis out there than we can actually count."
Dr Giola said it was an ancient disease, whose history could be counted in centuries, and there had been resurgences of it around the world, starting in the early 2000s.
"New Zealand actually lagged behind the rest of the world, so the resurgence really began in New Zealand in 2011 onwards, and unfortunately we are still in the increasing phase."
The bacterial disease is easily diagnosed with a blood test and can be treated with a simple shot of penicillin.
But symptoms can go undetected and if untreated, some people can get late stage syphilis, which can damage the brain, heart and other organs, Giola said.
"The two main situations are when it can be dangerous is during pregnancy, when it can harm and even kill the baby in the womb or shortly after birth.
"And it can get particularly dangerous if it crosses the barrier between blood and brain and gives a brain infection which can have devastating consequences, like people going blind, going deaf, developing dementia. It can be a nasty disease."
Giola said people concerned about the disease should feel empowered to ask for a sexual health check and make sure a syphilis test was included.
"Too often we see people who think they have had a full STI check because they've had a urine test and a swab, that's not the case. In this day and age, a full STI check must include a blood check for HIV and syphilis."
Giola said finger pointing at people who did not practise safe sex was "not particularly helpful".
"As a society, we should probably make it as easy as possible to use condoms by promoting them, by making them available."
But he said while condoms decreased the risk of syphilis, they did not bring it down to zero.
"So there are other things that need to happen, like for example, better access to testing and better access to care, so that unsurprisingly requires investment in healthcare and in resources."
He said sexual health had "definitely" overlooked by the health system.
"Sexual health has been overlooked and underfunded for a long time. All across the political spectrum, under the Labour government and the National government, so it's not been a problem of this political party or the other one.
"It's almost like the less we speak about it, the better we feel, but actually it's not. Things are happening out there."