This study used a modified version of the Behavioral Model for Vulnerable Populations to examine the predisposing, enabling, and need factors associated with detectable viral load (VL). HIV status was measured using saliva and confirmed by blood. Of 797 persons enrolled, 193 were HIV positive and provided VL counts. A hierarchical multivariate logistic regression approach demonstrated that the predisposing factors of homelessness and recent substance abuse, particularly methamphetamine abuse, had a negative association with VL. The negative association of homelessness on VL was weakened with the introduction of enabling and need utilization factors. Mediation analysis indicated homelessness and HIV medication taking significantly associated with methamphetamine use as a predictor of detectable viral load. Guided policy to address substance abuse among those who are HIV positive is needed to improve biological outcomes.