The vast majority of recent syphilis cases have been in the Dublin, Kildare and Wicklow area, latest figures show.
Officials declared an outbreak of the sexually transmitted infection earlier this year, amid a rise in cases.
Data from the HPSC shows almost 500 cases of early infectious syphilis in Ireland this year so far, with the vast majority of those (79%) in Dublin, Kildare and Wicklow.
Speaking to The Hard Shoulder, Dr Naomi Petty-Saphon - a specialist in public health medicine - said cases of the STI had been increasing before the COVID-19 pandemic hit.
She explained: "With the pandemic, everything changed a bit, and there was a decrease in cases in early 2020.
“After that, the numbers started to increase again - and this year to date, we’ve had 498 cases of early infectious syphilis notified. That’s a 43% increase compared to the same period last year."
Many STIs are often most common in younger people in their early 20s, but Dr Petty-Saphon said syphilis is often more common in slightly older age groups.
She explained: “[We’re seeing most cases] between the age of 25 and 34. The majority of cases are in men… but we’re seeing an increase in cases among women.
“There are a number of ways you can contract it, including unprotected oral, vaginal and anal sex.
"You can also get it from skin-to-skin contact with a syphilis sore, and it can also be passed from mother to child during pregnancy."
The infection is easily treatable but can cause serious health problems for both men and women if left untreated.
Symptoms can include a sore or ulcer around the genitals, a rash on the body, tiredness and swollen lymph glands.
Safe sex
Anyone who is concerned is being urged to avail of an STI test, with a free online testing pilot - SH24 - available to residents in Dublin, Kildare, Wicklow, Cork and Kerry.
However, experts say the best way to protect yourself is to practice safe sex.
Dr Derek Freedman - a specialist in sexually transmitted diseases - says it's vital to get the message about safe sex practices out there.
He said: “All these infections are so easily treated once they’re dealt with. But preventing acquisition is one of the golden rules.
"What really we should be looking at today is the concept of quality sex - know the person you’re with, and at least have their name and mobile phone number. Start off with a condom until you know them well.
"Keep up protection, and give breakfast the next morning. Like any sport, give a return match.
“If you’ve a lot of partners, put them in Excel [document] so at least if there is a problem you can get back and tell them there has been a problem."
