Best Practice Guidance for Digital Contact Tracing Apps: A Cross-Disciplinary Review of the Literature. (Preprint)

BACKGROUND: Digital contact tracing apps (DCTAs) have the potential to augment contact tracing systems and disrupt Coronavirus 2019 (COVID-19) transmission by rapidly identifying secondary cases prior to the onset of infectiousness and linking them into a system of quarantine, testing and healthcare worker case management. The international experience of DCTAs during the COVID-19 pandemic demonstrates how challenging their design and deployment are. OBJECTIVE: To derive and summarize best practice guidance for the design of the ideal digital contact tracing app (IDCTA). METHODS: A collaborative cross disciplinary approach was used to derive best practice guidance for designing the IDCTA. A search of the indexed and grey literature was conducted to identify articles describing or evaluating DCTAs. Medline was searched using a combination of free text terms and MeSH search terms. Grey literature sources searched were the World Health Organisation (WHO) Institutional Repository for Information Sharing, the European Centre for Disease Control (ECDC) publications library and Google, including the websites of many health protection authorities. Articles which were acceptable for inclusion in our evidence synthesis were peer-reviewed publications cohort studies, randomised trials, modelling studies, technical reports, white papers and media reports which related to digital contact tracing. RESULTS: Ethical, user experience, privacy and data protection, technical, clinical and societal, and evaluation considerations were identified from the literature. The IDCTA should be voluntary and should be equitably available and accessible. User engagement could be enhanced by small financial incentives, enabling users to tailor aspects of the app to their particular needs and integrating DCTAs into the wider public health information campaign. Adherence with the principles of good data protection and privacy by design are important to convince target populations to download and use DCTAs. Bluetooth Low Energy is recommended for DCTA contact event detection, but combining it with ultrasound technology may improve DCTA accuracy. A decentralised privacy preserving protocol should be followed to enable DCTA users to exchange and record temporary contact numbers during contact events. The IDCTA should define and risk stratify contact events according to proximity, duration of contact and the infectiousness of the case at the time of contact. Evaluating DCTAs requires data to quantify app downloads, use among COVID-19 cases, successful contact alert generation, contact alert receivers, contact alert receivers that adhere to quarantine and testing recommendations and the number of contact alert receivers who subsequently are tested positive for COVID-19. The outcomes of DCTA evaluation should be openly reported to allow for wider public evaluation of the app. CONCLUSIONS: In conclusion, key considerations and best practice guidance for the design of the ideal digital contact tracing app were derived from the literature.