Study participants: city and country where study took place, study time frame, participants’ sex and/or gender, mean/median age and age range, primary (e.g., MSM, TW, SW, incarcerated) and secondary (e.g., mobile app/Internet use to find sex partners, IV drug use) risk-group characteristic(s), number of persons surveyed or studied for per group, HIV serostatus (when available), race, and ethnicity. Diagnostic criteria used to define syphilis infection, syphilis re-infection, and neurosyphilis (if applicable). Number and frequency of syphilis cases, including stage at diagnosis, number and frequency of cases of syphilis re-infection, and number and frequency of cases of neurosyphilis. Reported titers of diagnostic tests (e.g., RPR, VDRL) will be recorded when available.