Simon, a 32-year-old office worker, is recalled for review of routine monitoring tests for HIV pre-exposure prophylaxis (PreP), which he has been prescribed for 18 months.

His latest syphilis (Treponema pallidum) serology is consistent with recent infection, with a reactive enzyme immunoassay screening test confirmed by T. pallidum haemagglutination and a strongly reactive rapid plasma reagin test at 1:64.