Effects of highly active antiretroviral therapy and its adherence on herpes zoster incidence: a longitudinal cohort study

BACKGROUND Herpes zoster (HZ) is common among HIV-infected individuals, but the impacts of highly active antiretroviral therapy (HAART) and HAART adherence on HZ risk have not been well studied. METHODS The effects of HAART and HAART adherence on HZ incidence were evaluated by comparing HIV-infected women on HAART (HAART use group) with the HIV-infected women remaining HAART naïve (HAART naïve group) in the Women's Interagency HIV Study (WIHS). A 1:1 matching with propensity score for predicting HAART initiation was conducted to balance background covariates at index visit, including HIV disease stage. Kaplan-Meier method was used to compare the risk of HZ development between the matched pairs. Cox proportional hazard models were used to assess the effects of HAART and HAART adherence on HZ incidence. RESULTS Through propensity score matching, 389 pairs of participants were identified and they contributed 3,909 person years after matching. The background covariates were similar between the matched pairs at the index visit. The participants had a mean age around 39 years old, and about 61% of them were Black and 22% were Latina. No significant difference in HZ risk was observed between the HAART use group and the HAART naïve group during the first year of follow-up in any analyses. In the univariate analysis, the HAART use group had marginally lower HZ risk (Hazard Ratio (HR): 0.72; 95% Confidence Interval (CI): 0.48-1.1) over the entire follow-up period. However, women with a HAART adherence level of ≥95% had significantly lower HZ risk (HR: 0.54; 95% CI: 0.31, 0.94) compared to the HAART naïve women. The association remained significant after adjusting for quality of life score and acyclovir use, but it attenuated and was no longer statistically significant after adjusting for an intermediate variable, either CD4+ T cell counts or HIV viral load. CONCLUSIONS Among adult women, we observed a significant preventive effect of long-term HAART use on HZ incidence when a HAART adherence level of ≥95% was attained, and this effect was mediated through reduction of HIV viral load and improvement of CD4+ T cell counts.