Fig. 1

Definition of HCV exposure peri-incident syphilis or chlamydia. Four consecutive HCV exposure intervals in the same patient (numbered 1–4): 2, 3: These HCV exposure intervals are included as peri-incident syphilis or anorectal chlamydia: 1, 4: These HCV exposure intervals are not included as peri-incident syphilis or anorectal chlamydia. Notes: An HCV exposure interval is the period between a negative HCV antibody test and the following HCV antibody test. An HCV testing exposure period is peri-incident syphilis or peri-anorectal chlamydia if it overlaps with an interval extending from 180 days before to 180 days after the period between a negative syphilis or anorectal chlamydia test and an immediately following positive syphilis or anorectal chlamydia test