Short Communication: The Interaction of HIV Set Point Viral Load and Subtype on Disease Progression.

HIV-1 subtype and viral load set point have been implicated as strong predictors of HIV-1 disease progression; however, the relationship between these two variables has not been investigated. We used data from the Rakai Community Cohort Study to investigate whether the association between viral load set point and disease progression is modified by HIV subtype. Time to AIDS or AIDS-related death was estimated by Kaplan-Meier survival analysis stratified by subtype and viral set point, and Cox proportional hazards regression with an interaction term between viral load set point and HIV subtype. The interaction term did not indicate effect measure modification between viral load set point and progression to AIDS by HIV-1 subtype [adjusted hazard ratio (aHR), 0.99; 95% confidence interval (CI) 0.61-1.61; p = .968]. Stratifed analysis by subtype was also not indicative of a difference in relationship between viral load set point and time to AIDS with overlapping 95% CIs between subtypes A and D (subtype A aHR: 2.40, 95% CI 1.45-3.99, subtype D aHR: 1.96, 95% CI 1.60-2.40). These results indicate that the higher mortality in subtype D-infected individuals is independent of viral load set point.