Improper use of TDF/FTC PrEP leading to acute HIV infection with low-level viremia and transient K70KR mutation: diagnostic challenges and drug resistance dynamics.

Background: Pre-exposure prophylaxis (PrEP) has demonstrated high efficacy in preventing HIV infection among men who have sex with men (MSM). However, improper use can lead to breakthrough infections and diagnostic challenges.

Case presentation: We report the case of a 30-year-old MSM who was prescribed on-demand PrEP with tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) via telemedicine, following baseline assessments that included a negative HIV antibody test and an undetectable pooled (10-sample) HIV-1 nucleic acid testing (NAT). Five months after initiating PrEP treatment, pooled NAT reported a positive result, while the HIV antibody test remained negative. In the subsequent month, HIV antibody seroconversion was observed; however, the viral load remained at a low level (< 1,000 copies/mL), and Western blot (WB) results were indeterminate. Genotypic testing identified a transient K70KR mutation. Four months after the first positive NAT, WB positive seroconversion occurred, accompanied by an increased viral load (14,064 copies/mL). Subsequently, the patient initiated treatment with Bictegravir/Emtricitabine/Tenofovir Alafenamide and achieved viral suppression within three months.

Conclusions: Improper and irregular use of PrEP led to HIV infection in this case. Telemedicine providers should conduct thorough assessments before starting PrEP and offer ongoing adherence support to maximize its effectiveness. This case highlights the importance of using NAT for early HIV detection in PrEP users and suggests including NAT in follow-up assessments to catch PrEP failures early. There is no need for excessive concern regarding the transient drug resistance mutations that may arise following PrEP failure, as these mutations do not compromise the efficacy of HIV treatment.