LONDON (Reuters) - Syphilis cases have soared in Europe over the last decade and become, for the first time since the early 2000s, more common in some countries than new cases of HIV, health experts said on Friday.

Reported cases of the sexually transmitted disease are up by 70% since 2010, a report from the European Centre for Disease Prevention and Control (ECDC) showed - with the rise driven by more unprotected sex and riskier sexual behavior among gay men.

“The increases in syphilis infections that we see across Europe ... are a result of several factors, such as people having sex without condoms and multiple sexual partners, combined with a reduced fear of acquiring HIV,” said Andrew Amato-Gauci, an ECDC expert on sexually transmitted infections.

The European report comes after the World Health Organization said last month that around a million people each day worldwide catch a sexually transmitted infection.

Left untreated, syphilis can have severe complications in men and women, including causing stillbirths and newborn deaths and increasing the risk of HIV. Syphilis was one of the leading causes of baby loss globally in 2016.

The Stockholm-based ECDC, which monitors health and disease in Europe, said that overall, more than 260,000 syphilis cases were reported from 30 countries from 2007 to 2017.

In 2017, syphilis rates reached an all-time high with more than 33,000 reported cases, the ECDC said. This meant that for the first time since the early 2000s, the region reported more cases of syphilis than new cases of the human immunodeficiency virus (HIV) that causes AIDS.

But the problem varied significantly by country, with rates more than doubling in five countries - Britain, Germany, Ireland, Iceland and Malta - but dropping by 50% or more in Estonia and Romania.

Close to two-thirds of the cases reported between 2007 and 2017 where sexual orientation was known were in men who have sex with men, the ECDC report said, while heterosexual men contributed 23% of cases and women 15%.

The proportion of cases diagnosed among men who have sex with men ranged from less than 20% in Latvia, Lithuania and Romania to more than 80% in France, Germany, Ireland, the Netherlands, Sweden and Britain.

Amato-Gauci said complacency among men who have gay sex and seem unconcerned about HIV risks appeared to be fuelling the problem. “To reverse this trend, we need to encourage people to use condoms consistently with new and casual partners,” he said.