Intervention fidelity and factors affecting the process of implementing a mobile phone text messaging intervention among adolescents living with HIV: a convergent mixed-methods study in southern Ethiopia.

Objective: To assess the intervention fidelity and explore contextual factors affecting the process of implementing a mobile phone text messaging intervention in improving adherence to and retention in care among adolescents living with HIV, their families and their healthcare providers in southern Ethiopia.

Design: A convergent mixed-methods design guided by the process evaluation theoretical framework and the Reach, Effectiveness, Adoption, Implementation and Maintenance framework was used alongside a randomised controlled trial to examine the fidelity and explore the experiences of participants in the intervention.

Setting: Six hospitals and five health centres provide HIV treatment and care to adolescents in five zones in southern Ethiopia.

Participants: Adolescents (aged 10-19), their families and their healthcare providers.

Intervention: Mobile phone text messages daily for 6 months or standard care (control).

Results: 153 participants were enrolled in the process evaluation. Among the 153 enrolled in the intervention arm, 78 (49.02%) were male and 75 (43.8%) were female, respectively. The mean and SD age of the participants is 15 (0.21). The overall experiences of implementing the text messages reminder intervention were described as helpful in terms of treatment support for adherence but had room for improvement. During the study, 30 700 text messages were sent, and fidelity was high, with 99.4% successfully delivered text messages during the intervention. Barriers such as failed text messages delivery, limitations in phone ownership and technical limitations affected fidelity. Technical challenges can hinder maintenance, but a belief in the future of digital communication permeates the experiences of the text message reminders.

Conclusions: Overall fidelity was high, and participants' overall experiences of mobile phone text messages were expressed as helpful. Contextual factors, such as local telecommunications networks and local electric power, as well as technical and individual factors must be considered when planning future interventions.

Trial Registration Number: PACTR202107638293593.