To the Editors:
Antiretroviral agents as preexposure prophylaxis (PrEP) against HIV-1 infection are a recent and welcome addition to the prevention toolbox. Clinical trials have shown tenofovir disoproxil fumarate/emtrcitabine (TDF/FTC) as PrEP to be safe and associated with substantial reductions (44%–86%) in the rates of HIV-1 acquisition in men who have sex with men (MSM) and transgender women,1–4 heterosexual HIV-discordant couples,5 and high-risk heterosexual men and women.6 In July 2012, the U.S. Food and Drug Administration approved the use of TDF/FTC as PrEP in combination with safer sex practices to reduce the risk of sexually acquired HIV-1.
Important lessons of PrEP use have emerged from clinical trials. Efficacy is highly dependent on adherence.7 Self-reported adherence, however, is of limited positive predictive utility. Indeed, objective measures of adherence (eg, drug levels in plasma and peripheral blood mononuclear cells) proved critical to study interpretation. For instance, in clinical trials, individuals randomized to active treatment who acquired HIV-1 infection had low or undetectable tenofovir (TFV) levels in plasma or TFV-diphosphate (TFV-DP) in peripheral blood mononuclear cells2,8,9 indicating poor adherence. Because of the relatively short half-life of TFV in blood plasma, however, this metric indicates the timing of the last dose and not longer-term adherence.10 The measurement of TFV-DP in red blood cells using dried blood spot (DBS) technology11 and TFV in hair samples12 indicates cumulative dosing and longer-term use and has proven valuable in interpreting subsequent open-label studies.
In this article, we present a case report of a young MSM in an HIV-serodiscordant relationship who was prescribed PrEP and, despite reportedly high-level adherence, became infected with HIV-1.
This 26-year-old MSM had been tested for HIV-1 infection routinely and deemed to be uninfected in January 2013, October 2013, and March 2015. Immediately before being prescribed TDF/FTC as PrEP in December 2015, a fourth-generation combination antigen/antibody (Ag/Ab) test was nonreactive and an HIV-RNA level was undetectable, consistent with his uninfected status. He was circumcised and had a history of treated urethral gonorrhea in September 2014. Of note, his regular partner had consistent virologic suppression on 3-drug antiretroviral therapy that had been initiated 4 years previously during acute infection.
The patient was prescribed a 90-day supply of PrEP with 1 refill which was commenced on January 1, 2016. He was seen on February 2, 2016 and was adherent by history and tolerating TDF/FTC. He presented on May 3, 2016, 5 months after PrEP initiation, for routine HIV-1 testing reporting excellent adherence to the prescribed regimen. He reported insertive condomless anal intercourse (ICAI) and receptive condomless anal intercourse with his regular partner and 2 separate episodes of ICAI with 2 different partners of unknown HIV status, 11 and 5.5 weeks before presentation. Results of HIV-1 testing are shown in Table 1. The reactive fourth-generation HIV test with a nonreactive HIV-1/2 Multispot and reactive qualitative testing for HIV-1 RNA by nucleic acid amplification test suggested recent HIV-1 infection. Supplemental tests were performed, as were tests for levels of plasma HIV-1 RNA and CD4+ T cells and results reported 2 weeks thereafter (Table 1). The results were consistent with extremely low levels of HIV-1 viremia and immune system preservation without seroconversion, and the treatment regimen was intensified with the addition of dolutegravir 50 mg daily to TDF/FTC on May 26, 2016. On June 7, the patient was reevaluated. To confirm the subject's self-reports of excellent adherence with his prescribed PrEP regimen, TFV and TFV-DP levels were measured in hair and DBS, respectively (Table 1). Results were consistent with high-level (eg, daily) adherence over the preceding 6–8 weeks,11,13 both prior and subsequent to the first indications of seroconversion.11,13
Since the patient's HIV-1 RNA level had been persistently below the level of detection, resistance testing on the virus in the plasma could not be performed. A GenoSure Archive test (Monogram), which derives HIV-1 sequences from cell-associated DNA, was sent on June 7 and failed to provide a result. On June 9, 2016, retesting revealed a reactive Bio-Rad GS HIV Combo Ag/Ab assay with both qualitative and quantitative HIV-1 RNA determinations being nondetectable. The Multispot HIV-1/2 Rapid test remained nonreactive (Table 1). By the current HIV testing algorithm, these results were reported as “no laboratory evidence of HIV infection,” despite the persistently reactive combo assay.
To determine whether the patient's partner was the source of infection, we amplified and sequenced the V3 loop of env, reverse transcriptase, protease, and integrase coding regions from HIV-1 viral DNA extracted from isolated CD4+ T cells from blood drawn on both patient and partner on June 9th (Supplemental Digital Content Fig. 1, http://links.lww.com/QAI/B76). Of note, the viral burden was extremely low in the newly infected patient, approximately 33.0 copies/106 CD4+ T cells on average that is orders of magnitude lower than typical viral loads among untreated individuals during early infection.14 Amplification of these coding regions proved challenging, and few sequences were available for comparison to those of his partner. However, phylograms demonstrated conclusively that the 2 individuals were infected with different viruses, as viral populations clearly segregate from each other (Supplemental Digital Content Fig. 1, http://links.lww.com/QAI/B76) and from additional viruses similarly analyzed.
Infection despite high-level adherence to TDF and FTC suggested acquisition of a virus resistant to the components of PrEP. Genotyping of the reverse transcriptase coding region on single genomes derived by limiting dilution polymerase chain reaction revealed linked mutations at K65R and M184V, resistance-conferring mutations to TDF and FTC, respectively,15 and additional mutations to nonnucleoside reverse transcriptase inhibitors, specifically K103S, E138Q, and Y188L15 (Table 1, Supplemental Digital Content Table 1, http://links.lww.com/QAI/B76). This individual was likely infected with a multidrug-resistant (MDR) virus, as the nonnucleoside reverse transcriptase inhibitor–associated resistance mutations would not have evolved under pressure by TDF/FTC alone. However, given that sampling was not performed at the time of infection, the possibility of evolution of resistance under pressure by TDF and FTC cannot be completely ruled out. Given that the patient harbored HIV-1 resistant to both TDF and FTC, coformulated cobicistat-boosted darunavir was subsequently added to the patient's treatment regimen to ensure continued and prolonged virologic suppression.
This is the second reported case of the acquisition of an MDR HIV-1 variant in an apparently adherent individual on TDF/FTC-based PrEP.16 In both cases, the patients reported excellent adherence confirmed by objective measurements of TDF use. However, these measurements could not be performed at the exact time of infection in both cases, so we can only extrapolate that adherence around the time of HIV acquisition was adequate.
As the number and risk of sexual exposures were highest with the patient's regular partner, the question of transmissibility from an HIV-infected individual with an undetectable viral load was raised. Our patient's regular partner had achieved consistent virologic suppression on antiretroviral therapy for approximately 4 years. In this case, it was critical that we documented that the suppressed regular partner was not the source of the new HIV-1 infection in our index patient. The patient reported only ICAI with nonregular partners, and although ICAI carries a much lower of HIV acquisition than RCAI (11 versus 138 HIV-1 infections per 10,000 exposures), this case does demonstrate the importance of counseling MSM as to the per-act probability of HIV-1 acquisition.17
For our patient, repeated testing with the fourth-generation Ag/Ab combination test was reactive. As HIV-RNA levels were either barely or nondetectable, the presence of antibodies to HIV-1 was suggested, although the confirmatory immunoassay (Multispot HIV-1/2) remained repeatedly nonreactive over 5 weeks. Delayed seroconversion may be observed in those administered combination antiretroviral therapy during acute infection18 and in one other case report of an individual becoming HIV infected during repeated courses of postexposure prophylaxis with TDF/FTC.19 Essential to this case is that the combination of the reactive fourth-generation combination Ag/Ab test and the qualitative nucleic acid amplification test established the diagnosis of HIV infection. These findings highlight the importance of using sensitive HIV tests in the context of PrEP delivery.20
In summary, newly acquired HIV-1 infection in patients being treated with PrEP and with evidence of adequate adherence as assessed through objective measures is rare. To date, there have been 2 such cases of acquisition of MDR HIV-1 and a recent report of infection with wild-type HIV-1 in an MSM with repeated exposures through CAI,21 despite more than 86,000 people using PrEP in the United States. Such cases may pose clinical and laboratory challenges. Although sensitive fourth-generation tests were sufficient to detect infection in this case, subsequent recommended confirmatory testing following the 2014 Centers for Disease Control/Association of Public Health Laboratories HIV testing algorithm proved challenging. The limitations of testing in the face of a low viral burden may complicate testing efficacy. Objective adherence testing in this case proved useful. However, despite the high effectiveness of TDF/FTC as PrEP in highly adherent individuals, the level of protection, if any, against infection by circulating viruses resistant to both medications is not known. Although the transmission of MDR HIV-1 has fallen over the past decade,22,23 this case, as well as the “Toronto case,” highlights the importance of awareness of the potential risk of MDR HIV-1 viral transmission despite PrEP use. Surveillance for drug resistance among people who become infected after receiving PrEP is needed to evaluate whether these cases will remain rare.
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