Developing mHealth to Promote PrEP Use Among Thai Young Vulnerable Adolescents and Emerging Adults

System Usability Score (SUS) is a 10-item, Likert scale used to calculate intervention usability. Each item ranges from 0 to 4 (with 4 being the most positive response). For odd-numbered items, the score is calculated by subtracting one from the user response. For even-numbered items, the score is calculated by subtracting the user response from 5. Then sum the total score and multiply that by 2.5. The overall SUS scores range from 0 to 100. A score of > 50 indicates that the technology-based interventions are acceptable.

System Usability Score (SUS) is a 10-item, Likert scale used to calculate intervention usability. Each item ranges from 0 to 4 (with 4 being the most positive response). For odd-numbered items, the score is calculated by subtracting one from the user response. For even-numbered items, the score is calculated by subtracting the user response from 5. Then sum the total score and multiply that by 2.5. The overall SUS scores range from 0 to 100. A score of > 50 indicates that the technology-based interventions are acceptable.

Client Satisfaction Questionnaire (CSQ-8) is an 8-items, Likert scale measuring the construct of global intervention satisfaction. The total possible composite score range from 8 to 32, with higher scores indicating a greater degree of acceptability.

Client Satisfaction Questionnaire (CSQ-8) is an 8-items, Likert scale measuring the construct of global intervention satisfaction. The total possible composite score range from 8 to 32, with higher scores indicating a greater degree of acceptability.

Intervention acceptability will be assess by the number of positive responses based on the exit interviews administered at month 1. Participants will be asked to provide feedback on experiences using MES-PrEP and enhanced YaCool, acceptability and ease of use, suggestions for improvement, role in PrEP uptake and adherence, and interest in continued intervention use, as well as experiences following a PrEP regimen, reasons for discontinuation of PrEP, and additional tools that would assist them in taking PrEP.

Intervention feasibility will be measured by total number of responses to and frequency of usage of Enhanced YaCool. Point estimates of >50% of participants responded to Enhanced YaCool at least once is considered as the minimum criteria for feasibility.

Intervention feasibility will be measured by number of intervention sessions completed. Point estimates of >50% of participants completed at least one intervention session is considered as the minimum criteria for feasibility.

Intervention Feasibility will be measured by participants retention rate at Month 6. Retention rate of >85% at month 6 is considered as the minimum criteria for feasibility.

PrEP adherence will be measured from Young Adult Adherence Interview via computer-assisted self-interview (CASI) survey which contains a visual analog scale (VAS). VAS ranges from 0 to 100, with higher percentage indicating greater adherence to PrEP.

PrEP adherence will be measured from self-reported adherence to PrEP in the past 4 weeks via CASI survey. The scale ranges from 0 to 100%, with higher percentage indicating greater adherence to PrEP. The result of this self-reported adherence will be triangulated with the results of dried blood spots testing.

PrEP adherence will be measured by the level of tenofovir in dried blood spots (DBS). DBS report on 80% Truvada adherence after at least three weeks of regular adherence.

PrEP uptake will be measured by the number of PrEP prescription, using a self-report measure (participants reporting if they left the clinic with PrEP) and confirming with clinic records.

Knowledge of PrEP will be measured using the 13-item PrEP knowledge scale. The total possible score is 13, with higher scores indicating a greater degree of PrEP knowledge.

Knowledge of HIV transmission risk will be assessed using am 18-item HIV Knowledge Questionnaire. The total possible composite score range from 0 to 18, with higher scores indicating a greater degree of HIV knowledge.

Behavioral intentions will be measured using 5-item Rollnick's Readiness Ruler, which correspond to PrEP uptake and adherence. Each item ranges from 0 to 10, with higher numbers indicate greater readiness for change.

Attitude towards PrEP will be measured using 36-item Decisional Balance for PrEP Use. The 5-point Likert scale assesses the pros and cons of PrEP use and is helpful in understanding cognitive and motivational aspects of decision making.

Behavior skills will be assessed using the 8-item adapted version of Self-Efficacy for Health Promotion and Risk Reduction Questionnaire. The 5-point Likert scale assesses the confidence in using a condom, taking PrEP as recommended and getting PrEP refills. The total possible score is 40, with higher scores indicating a greater confidence for each item.

HIV status based on 4th generation HIV-1/2 antigen/antibody combo testing.

STI diagnosis based on treponemal test with rapid plasma reagin (RPR) confirmation for syphilis. Pooled urine, oropharyngeal and rectal swabs for gonorrhea and chlamydia nucleic acid amplification test (NAAT) testing.

Sexual risk will be assessed through Timeline Followback via CASI, which collects sexual behavior in the past 30 days, including questions about condom use and number of sexual partners.

Drug/Alcohol Use will be assessed using Alcohol, Smoking and Substance Involvement Screening Test (ASSIST) developed by the World Health Organization (WHO). ASSIST is a questionnaire that is used for identification of substance use related health risks and substance use disorders. Each item ranges from 0-12, with 0 reflecting low risk score. The total possible score is 24, with higher number indicating higher risk of health and other problems based from the current pattern of substance use.

Alcohol Use Disorders Identification Test (AUDIT-C) or a brief alcohol screening instrument will also be used to identify persons who are hazardous drinkers or have active alcohol use disorders (including alcohol abuse or dependence). Each item ranges from 0 to 4, with 0 reflecting no alcohol use. The total possible score is 12, with higher number indicating higher drink above recommended limits and are at increased risks for harm.

Mental Health will be assessed using the 12-item Thai General Health Questionnaire. The 4-point Likert scale measures psychological distress such as depression, anxiety, social impartment and somatic complaints. The total possible score is 48, with higher scores indicating higher severity of psychological distress.

Perceived HIV risk will be measured using the 8-item Perceived Risk of HIV Scale. All items are rated on a 4-point Likert scale. The total possible score is 40, with higher scores indicating higher perception of HIV risk.

Social support will be assessed using the 13-item Social Provision Scale (SPS). The 5-point Likert scale measures the availability of social support, including emotional support, information support, instrumental support, companionship and social isolation. The total possible score is 65, with higher scores indicating greater availability of social support.

PrEP-related stigma will be assessed using the 10-item PrEP stigma and positive attitudes scale. The 5-point Likert scale measures opinions about PrEP. Higher scores indicate higher perceived stigma related to PrEP.