The syphilis outbreak is now the worst it has ever been in New Zealand, with health professionals urging people to take extra precautions.
A total of 470 New Zealanders were reported to have syphilis last year, which was more than double the number of cases there were in 2015.
Rates of syphilis are at the highest ever in Auckland and Wellington.
Family Planning national medical advisor Beth Messenger said it was important everyone understood what the infection was, how it could be prevented and how it could be treated.
"It is vital that we stop the spread of syphilis now."
Syphilis usually starts as an ulcer on the skin or lining of the genital area and was highly contagious.
Messenger said although syphilis was spread through these lesions, most cases went unrecognised.
"Usually people aren't aware that they have syphilis, so they unknowingly pass it on through unprotected oral, vaginal or anal sexual activity."
In its late stage, syphilis could cause damage to the heart, brain and spinal cord.
Some of the worst outcomes included becoming paralysed, blindness, dementia, arthritis, deafness, impotence, and even death if untreated.
New Zealand babies were also dying from syphilis being passed on from their mothers during pregnancy.
All women should be screened for syphilis early in pregnancy. However, in July the Herald confirmed cases – including a stillbirth – where that crucial testing wasn't done.
There have been four cases of congenital (mother-to-baby) syphilis since 2017, and one probable case.
Syphilis has four stages – it start with a single painless chancre, though there may be multiple lesions. In the secondary stage, rashes occur usually on the palms of hands and soles of feet.
Other symptoms include fever, sore throat, weight loss, hair loss and headache.
But at each stage it can be treated with antibiotics.
Messenger said people with syphilis, even with treatment, needed to tell their sexual partners so they could be treated too.
STI (sexually transmitted infection) tests should be taken when:
• You and a new partner are beginning a sexual relationship.
• You have had unprotected sex.
• You think you may have an STI.
• A condom broke.
• You are pregnant.
• You have symptoms or just feel something is not right.
• You have had sex – anal or vaginal – with an HIV-positive partner
• You have injected drugs and shared needles or works (for example, water or cotton) with others.
• You have exchanged sex for drugs or money.
• You have had sex with someone who could answer "yes" to any of the above questions or someone whose sexual history you don't know.