Cognitive interviewing to validate IFUS. Convenience sampling will be used to recruit clients from VCT clinics for the cognitive interviews. Eligibility criteria include clients who are 16 years or older, and willing to provide written informed consent for participation in the study. A witnessed thumbprint will be sufficient for those who are unable to read or write. Participants will be purposively selected to ensure a range in location and literacy level. Four to 12 participants will be recruited for each iteration of the cognitive interviews, with a maximum of 12 iterations of adaptation and trial of the intended IFUs (n = 144). Cognitive interviewing and iterative adaptation will continue until saturation occurs and no further modifications to user materials are made.