No new HIV infections have occurred among nearly 5000 people who started Truvada for pre-exposure prophylaxis (PrEP) in the Kaiser Permanente Northern California health system, according to a letter in the 29 July edition of Clinical Infectious Diseases.
However, there were some infections in people who sought PrEP but decided not to take it or who started but then stopped, indicating missed opportunities for HIV prevention at various steps of the 'PrEP cascade'.
"Strategies are critically needed to ensure that patients start, restart or continue PrEP during periods of risk for HIV acquisition," the researchers concluded.
A growing body of research has demonstrated that daily or on-demand Truvada (tenofovir disoproxil fumarate/emtricitabine) is highly effective at preventing HIV when used consistently. Only three cases of PrEP failure have been reported under those circumstances (see report from CROI 2016, report from HIVR4P 2016 and report from CROI 2017).
Julia Marcus of Harvard Medical School and colleagues from the Kaiser Permanente Division of Research and Kaiser Permanente San Francisco Medical Center looked at the risk of PrEP failure defined more broadly, as occurring at any point along the continuum of care from the time a person first sought or was referred for PrEP through to ongoing consistent Truvada use.
This study included 7124 people who sought or were referred for PrEP at Kaiser Permanente Northern California from July 2012 through February 2017. Most were men who have sex with men.
Kaiser Permanente Northern California, an integrated system that provides comprehensive medical services to more than 4 million members, has one of the largest PrEP programmes in the United States. Kaiser researchers previously reported no new HIV infections among its PrEP users, though they found that sexually transmitted infection rates were high, and they saw two unusual cases of apparently sexually transmitted hepatitis C virus in HIV-negative gay men.
Of those seeking or referred for PrEP, 26 members (0.4%) were diagnosed with HIV during their assessment for PrEP eligibility. Of the remaining individuals, 70% started PrEP and 30% opted not to do so.
Among the 4991 people who started PrEP, the mean duration of use, estimated from the time a first Truvada prescription was filled until the last filled prescription ran out, regardless of gaps in use, was 12.4 months. No new HIV infections occurred during more than 5000 person-years of Truvada use.
Among the 2107 people who did not start PrEP, 22 were later diagnosed with HIV, for an incidence rate of 1.1 per 100 person-years. And among the 1303 people who no longer had any Truvada left at the end of follow-up, 11 were diagnosed with HIV after their last filled prescription ran out, for an incidence rate of 1.3 per 100 person-years.
"We identified no HIV infections during more than 5,000 person-years of PrEP use, consistent with the high adherence previously observed in this setting," the researchers wrote.
"However, HIV infections were identified among individuals who were being assessed for PrEP eligibility (ie, late to access PrEP), who sought or were referred for PrEP but did not start (ie, failure to initiate PrEP), or who discontinued PrEP (ie, failure to be retained in PrEP care)."
Marcus JL et al. Redefining HIV preexposure prophylaxis failures. Clinical Infectious Diseases, 2017. See https://doi.org/10.1093/cid/cix593