Syphilis cases have soared in Europe over the last decade, Reuters reports.

Syphilis cases are more common in some countries than new cases of HIV for the first time since the early 2000s, health experts warn.

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. The rise is driven by more unprotected sex and riskier sexual behavior among gay men.

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.

Unprotected sex and riskier sexual behavior

Several factors are crucial for the rise of syphilis cases, said Andrew Amato-Gauci, an ECDC expert on sexually. These include:

• People having sex without condoms
• Multiple sexual partners
• Reduced fear of acquiring HIV

More than 260,000 syphilis cases were reported from 30 countries from 2007 to 2017, states the Stockholm-based ECDC, which monitors health and disease in Europe. In 2017, syphilis rates reached an all-time high with more than 33,000 reported cases. 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.

Most cases with men who have sex with men

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.

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, Reuters reports.

Severe complications from syphilis

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.