Germany had 5,722 new cases of syphilis in 2014 - an increase of 14 percent over the year before, according to a new report by the Robert Koch Institute (RKI).
The number of syphilis cases in Germany has been increasing each year since 2010, after spread of the infection started to stagnate and even slightly decline in the mid-2000s. The first half of 2015 also seemed to show a continued increase in cases, the report said.
Syphilis is a sexually transmitted infection (STI) that is contracted through sexual contact, as well as from mother to child at birth. The infection has various stages, the first of which is characterized by sores, the second by a skin rash and sometimes fever.
Untreated cases can lead to death.
The institute said in the report published on Monday that most of the spread of the STI was between men, with 84 percent of new cases believed to be contracted from one man to another.
The vast majority of patients with syphilis were men, with women making up just 6.3 percent of new cases, a slight decrease since the year before.
The influence of party drugs could be a cause for the increase in cases, said Professor Norbert Brockmeyer, president of the German Society for Sexually Transmitted Diseases (DSTIG). Such drugs may reduce the user's awareness of possible risks, he argues.
Berlin is syphilis hotspot
The report also showed a great geographical variance across the country in terms of which regions had the most cases.
Berlin had by far the highest proportion of syphilis cases across the 16 states, with 31 diagnoses for every 100,000 residents. In comparison, the country average was 7.1 cases for every 100,000 residents.
Meanwhile, the state of Brandenburg which surrounds Berlin had one of the lowest rates at about half the national average, along with Thuringia and Schleswig-Holstein.
Hamburg had the second-highest rate at 19.7 cases per 100,000. All other states had rates of 7.2 per 100,000 or less.
Big cities across the country had higher than average rates of syphilis, with Cologne (31.9 cases per 100,000) and Munich (27.2) also recording high incidences.
But a third of the cases nationwide happened in towns with less than 100,000 citizens.