Retreatment

They report that 6 percent of new cases and 35 percent of retreatment cases are drug-resistant to more than one medication.

In Europe, when people have syphilis infection they are treated very aggressively and their medical history is flagged, McKenna said. She recommends similar treatments for primary syphilis, including aqueous penicillin, and retreatment and reevaluation for two years on a regular basis.