Men who have sex with men are at the highest risk for syphilis. (Bigstock)

Men are being warned after new cases of syphilis hit their highest rates in almost 70 years.

The sexually transmitted infection is at its highest number of cases since 1949, according to data from Public Health England (PHE).

In 2016 there were 5,920 syphilis diagnoses, a 12% increase on the previous year’s figure (5,281).

The number marks an incredible 97% rise since 2012 (3,001).

Experts say most cases were transmitted by gay and bisexual men, and other men who have sex with men.

Dr Michael Brady, the medical director for the Terrence Higgins Trust, a sexual health charity, said: “Today’s figures show unacceptably high rates of STIs.

“We’re facing huge challenges, such as the continued rise of syphilis and ongoing concerns around drug-resistant gonorrhoea, and we urgently need to address the nation’s poor sexual health and rates of STIs in those most at risk.

“In this climate of cuts to local authorities’ public health budgets, this is particularly concerning.

“Now is not the time to be scaling back sexual health services.

“Cuts to chlamydia testing, for example, are having a visible impact, with today’s figures showing that there has been a 9% decrease in the number of chlamydia tests taken.

“It is also now essential that Public Health England, the Department of Health and local authorities ensure improved access to effective STI and HIV testing, treatment and prevention services. Otherwise, we cannot expect to address the ongoing sexual health crisis.”

There is some positive news about sexually transmitted infections, though.

In the same time frame new infections of HIV in men who have sex with men have fallen by a third.

It is believed this is mainly due to the significantly increased use of PrEP.

Dr Patrick French, CNWL Consultant in Sexual Health and HIV, said: “There is some room for optimism in today’s release of the 2016 Sexually Transmitted Infection and HIV figures from Public Health England.

“The dramatic reduction in the number of new HIV infections among gay men shows that HIV testing, HIV treatment and Pre-Exposure Prophylaxis are paying dividends and the reduction in genital warts in heterosexual women and men indicate that HPV vaccination for girls in the UK is working well.”