Conference Coverage

Nucleic acid testing before PrEP urged to detect occult HIV



– Almost a third of patients who developed HIV while on pre-exposure prophylaxis (PrEP) had strains that were resistant to emtricitabine – a component of the PrEP medication Truvada along with tenofovir – at time of diagnosis, compared with just 2% of those not on PrEP, in a review of more than 3,500 newly diagnosed HIV cases in New York.

Dr. Kavita Misra, New York City Department of Health and Mental Hygiene M. Alexander Otto/MDedge News

Dr. Kavita Misra

The finding points to a growing concern as use of PrEP becomes more common: the induction of resistance to HIV treatments.

PrEP is highly effective, so it’s likely that the PrEP patients already had HIV when they started treatment. Nucleic acid amplification testing (NAAT) is the only way to rule it out definitively, but only 5% of PrEP users in the study were screened with NAAT within 2 days of initiation.

The usual test – HIV antibody screening – returns a false negative in the window between HIV exposure and active infection, when antibodies turn positive, which can take months. NAAT, on the other hand, looks for evidence of the virus directly.

The findings led the investigators to urge routine NAAT screening before PrEP, something that New York State guidelines currently recommend only if patients present with symptoms of acute HIV infection or report condomless sex in the previous 4 weeks.

To prevent drug resistance, “rigorous screening that includes NAAT is critical.” It reduces “the likelihood of PrEP start during undetected HIV infection,” said lead investigator Kavita Misra, PhD, MPH, a senior epidemiologist at the New York City Department of Health and Mental Hygiene.

Her team reviewed 3,685 people in New York who were diagnosed with HIV from November 2015 to August 2017; 91 had been on PrEP beforehand for a median of 106 days.

Postdiagnosis genotyping was available for 75% of PrEP users and 63% in the no-PrEP group. Resistance mutations to emtricitabine were significantly more prevalent with PrEP than without (29% versus 2%, respectively; P less than .0001). None of the PrEP users, but four in the no-PrEP group, had resistance to the other component of Truvada, tenofovir.

PrEP users were more likely to be diagnosed with HIV in the acute phase of infection than were those not using PrEP (33% versus 9%; P less than .0001), probably because they were also more likely to have regular office visits while on PrEP.

Skeptics at the Conference on Retroviruses and Opportunistic Infections, where the study was presented, wondered whether emtricitabine resistance would have been more common in the no-PrEP group if the infection had been picked up earlier because resistance fades as the infection progresses.

Dr. Misra said it was a good question and that her team will look into it. However, she stood by her conclusions.

PrEP use was most common among white men who have sex with men and among people under 30 years old.

There was no external funding, and the investigators didn’t have any disclosures.

SOURCE: Misra K et al. 2019 CROI, Abstract 107.

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