Search strategy

We carried out a systematic computerized literature search for RCTs and observational studies on patients who received penicillin, doxycycline, tetracycline, or ceftriaxone treatment for early syphilis. PubMed, Cochrane Central Register of Controlled Trials, Embase, the Web of Science, and ClinicalTrials.gov were searched from inception to June 30, 2016 by combining Medical Subject Headings (MeSH) descriptors with free text terms to identify relevant studies; and appropriate adjustment was made as database varied (S2 Table). The references of the included articles and documented meta-analyses were also retrieved manually to widen the scope of literature search.