The increase has been particularly significant in men who have sex with men (MSM) according to HPSC.

While the centre said that cases of most sexually transmitted infections remained relatively stable in 2015 compared to a year earlier, its specialist in public health medicine, Dr Derval Igoe, said: “We are concerned about a 50% increase in syphilis, and a 30% increase in HIV cases in 2015.

“Although some of the increase in HIV can be explained by a change in the notification procedures for HIV and an outbreak in people who inject drugs, these increases have largely being seen in MSM.

“MSM account for four-fifths of the syphilis cases, and more than half of the HIV cases. For HIV, an increasing proportion of MSM born abroad, and particularly from Latin America, who were HIV positive before coming to Ireland, has contributed to this. There are also increases in the number of MSM from abroad who report acquiring HIV in Ireland.”

She said that while gonorrhoea numbers last year were similar to 2015, the latest data for the first six months of this year showed that instances of the infection had risen by 63%.

The HSE pointed to a recent survey on sexual behaviours in MSM in Ireland which showed that 25% of men have had condomless anal intercourse with more than one partner in the last year, posing a risk of acquiring or transmitting HIV and STIs. It found 37% of men had never been tested for HIV and 38% had never been tested for an STI.

Meanwhile, it has been claimed an experimental immunotherapy drug could herald a “breakthrough” in the treatment of HIV and Aids.

In early tests, rhesus macaques given the antibody showed sustained recovery from infection by the monkey equivalent of the HIV virus. Within four weeks of receiving the therapy, almost no SIV (simian immunodeficiency virus) could be detected and two years after finishing the treatment, levels of the virus remained below the threshold considered harmful. The monkeys appeared healthy and their immune systems functioned efficiently.

The antibody used was a tweaked variant of the drug vedolizumab which has been available since 2014 in the US and Europe to treat bowel diseases such as Crohn’s and ulcerative colitis.