Researchers are seeing an alarming rise in a sexually transmitted infection

The number of syphilis cases being reported nationwide jumped 45 percent between 2022 and 2023.

Auckland had the most - and almost triple the cases of the next highest, Waikato.

Men made up more than 80 percent of cases, with the rate doubling for those who are gay or bisexual.

Meanwhile rises are seen in almost every other demographic, including women, and those over the age of 40.