A 24-year-old man taking PrEP with unusual syphilis test results.

Introduction: The antiretroviral regime emtricitabine-tenofovir disoproxil fumarate (Truvada [Gilead Sciences]) is a type of pre-exposure prophylaxis (PrEP) therapy used for the prevention and management of HIV infections. This protection, however, cannot be applied to other sexually transmitted infections (STIs), with many studies observing an increase in STI rates among individuals using PrEP.

Methods: A 24-year-old man who had recently started PrEP with emtricitabine-tenofovir disoproxil fumarate was found to have a clinically significant elevation in syphilis total antibody count on STI screening, but his rapid plasma reagin (RPR) and Treponema pallidum particle agglutination (TP-PA) results remained negative. The patient was subsequently treated for a syphilis infection.

Results: Post-treatment testing showed a negative syphilis total antibody result. The patient was suspected to have undergone treponemal antibody seroreversion, a rare but previously documented phenomenon following successful treatment.

Discussion: This case highlights the possible effect of PrEP on the immune system, requiring closer surveillance to prevent acquisition of other STIs.