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Infectious diseases caused by pathogens can spread directly or indirectly from one person to another, similar to a chain reaction. When a pathogen infects a person, the time it takes for the symptoms to appear is called the incubation time or subclinical stage. The length of the incubation time differs from one pathogen to another. During this incubation, an exposed person should be in quarantine to prevent the spread of microorganisms (Virlogeux et al., 2015).
The incubation time for some pathogens may be as low as one day, but for others, the incubation time may be longer (CDC). For example, common cold-related viruses may have an incubation period of 1-3 days, an H5N1 virus for avian influenza has an incubation time of 2-5 days, whereas the COVID-19 virus may have an incubation time of up to 14 days. During the subclinical disease stage, an infected person might travel to various places, and the chance of spreading pathogens in the community is very high. The shorter incubation time for H5N1 resulted in this disease having a high concentration only in Asia, while the longer incubation time for COVID-19 has resulted in this disease becoming a global pandemic. To control the outbreak, comprehensive testing, contact tracing, and isolation are mandatory when dealing with infectious diseases (Hellewell et al., 2020; Salathé et al., 2020).
Figure 1 shows the exposure and incubation time for an infectious disease. Since no symptoms are evident during the incubation time, the likelihood of early detection of the disease is low. Contact tracing must be undertaken when a person has tested positive for the infection, but the length of the incubation period may vary from case to case. The most difficult problem in the contact tracing procedure is obtaining accurate information on the places the infected person visited during the incubation as some people might be reluctant to reveal details of their whereabouts due to privacy concerns (Travers et al., 2020). Most countries had either limited or completely halted international and domestic flights by Q2-2020 to prevent the spread of new cases. Several countries also implemented additional strategies to control the spread of the COVID-19 pandemic, such as conducting intensive testing throughout the nation (Sonn, 2020), digitally tagging those suspected of being infected (Mozur et al., 2020), imposing strict lockdowns with curfews (9News Staff, 2020). However, some countries such as Sweden did not impose a strict lockdown for its citizens; rather, it recommended that people practice social distancing, wear masks and work from home where possible. However, business, retail, and schools remained open (Thomas, 2020).
Figure 1. Exposure and incubation time
The proximity-based approach as implemented in COVID safe (Ministry of Health Australia, n. d.; Ministry of Health Israel, n. d.) PEPP-PT (PEPP-PT, 2020), SafePaths (Raskar, n. d.; Allheeib et al., 2020), StayHomeSafe (The Government of the Hong Kong Special Administrative Region, n. d.), and TraceTogether (Singapore, n. d.), using short-range wireless technology to identify nearby devices. Recent collaboration between Google and Apple resulted in the development of a framework for an Exposure Notification system for privacy-preserving contact tracing to overcome communication problems between two different platforms (Apple, n. d.). However, a recent report suggests that around 60% of the population must use a contact tracing app to ensure the system's effectiveness (Hinch et al., 2020). In Australia, despite the high number of COVID-19 cases, the COVIDsafe app has provided little assistance to health authorities, and the number of users of this application is still below the minimum required number (Meixner, 2020).