# Privacy and Security in Digital Health Contact-Tracing: A Narrative Review
## 1 Introduction  
In the fight against infectious diseases, tracing contacts to treat or isolate them, if necessary, is a crucial control strategy [1]. In traditional contact-tracing, health officials manually trace contacts of individuals who have tested positive for an infection. Those individuals are advised to self-monitor symptoms and to quarantine [2]. Reaching out to potential secondary cases is the primary goal of contact-tracing, which is an extreme form of targeted control. When the number of infectious cases is low, contact-tracing has demonstrated effectiveness as a strategy [1], reducing the spread of infectious diseases during epidemics, including severe acute respiratory syndrome-associated coronavirus (SARS-CoV) and Ebola [3, 4]. Traditional contact-tracing is labour-intensive and time-consuming, making it infeasible during pandemics [2].  
Digital contact-tracing identifies exposed individuals using technology, usually via Smartphone applications [5]. Their availability has enhanced traditional contact-tracing by providing timely and automated notifications, ultimately supporting public health efforts to curb transmission of infectious diseases. Digital contact-tracing was first introduced in March 2020 in Singapore [6] during the COVID-19 pandemic, only being a feasible option due to the wide ownership of Smart devices. In 2011, over 4 billion mobile deviceusers were identified, and this continues to rise [7]. Digital contact-tracing mechanisms became an integral part of disease prevention during the recent pandemic, mainly due to high transmissibility and fatality rates [8] of the COVID-19 virus. Digital contact-tracing solutions could be more efficient than traditional tracing [8] but acceptance was deterred by numerous challenges. People were reluctant to share their data with an unknown entity and did not feel the newly introduced system was trustworthy and authentic. Digital solutions also inherently suffer from privacy and security issues [9]. It has been reported that data collected by apps could be used in public or private investigations and may break developers' privacy policies [10]. This makes people even more sceptical about using digital contact-tracing apps that collect health data.  
Most countries introduced their first version of the contact-tracing app in 2020 during the COVID-19 pandemic period [6]. The low adoption rates directly impacted the app's effectiveness since these apps typically require over 60% of people to utilise them to achieve efficacy [11]. For effective contact-tracing, 80% of smartphone users need to use contact-tracing apps [8]. By December 2020, in the United Kingdom, only 28% had actively used the contact-tracing app [12]. During the pilot study of the first version of the contact-tracing app in the Isle of Wight, 56,000 downloads were observed, accounting for around 40% of the population [13]. In March 2021, Singapore and China reached the 60% threshold, while other countries had an adoption rate of around 15%, including Ireland, Canada, Germany, and Iceland [14].  
Many concerns arose over efficacy, battery and data usage, and data management of digital contact-tracing apps, while cybersecurity was also a major concern [15]. People's attitudes toward these technologies were influenced by various factors, including privacy concerns [16; 17; 18; 19; 20; 21; 22], technological issues [23; 24; 25], and perceptions of effectiveness [26; 27; 28; 25]. The aim of this review is to provide a comprehensive overview of the key issues associated with the acceptance of digital contact-tracing, with a primary focus on privacy and security assurances. This paper discusses psychological and behavioural factors that affect individuals' acceptance of digital health contact-tracing reported in the literature.