**1. Introduction**

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a type of highly infectious pathogen that is unique compared to many other viruses seen in recent history [1]. The virulent nature of SARS-CoV-2 has allowed it to set the stage for the current global pandemic that continues to plague our society, known as coronavirus disease 2019 (COVID-19) [1]. Over the last 2 years, COVID-19 has drastically altered the way in which humans have lived and is expected to continue with no foreseeable

end. As a result of the pandemic, people, businesses, and governments alike have been forced to adapt to continuously changing situations. The changes in people's daily routines, workplace habits, and social interactions over the past 2 years, only account for a fraction of the seemingly permanent COVID-19-induced changes [2]. Otherwise known as the COVID-19 experience, these adaptations and changes to our society are not limited to the experiences of average citizens. SARS-CoV-2 has also fundamentally altered how institutions such as the healthcare industry and governments respond to potentially pandemic-level infectious diseases, both in terms of diagnostic capabilities and social practices [2].

Unlike many other viruses in the same coronavirus family, SARS-CoV-2 was found to be sufficiently infectious and complex that it was not readily or accurately diagnosed in the early stages of the pandemic. SARS-CoV-2 almost always initially presents itself as a mild case of the common cold or seasonal flu virus [1]. These near-asymptomatic early-stage primary infections, coupled with the limitations in early diagnostic testing, have led to some of the highest rates of lethality and longlasting symptoms seen in the last century [3]. As of March 2022, it has been reported that COVID-19 has been officially linked to over 6,000,000 deaths worldwide. At one time, it was the second-leading cause of global deaths in both children and adults [3]. SARS-CoV-2's unique characteristic of presenting seemingly mild or asymptomatic cases continues to be one of the most difficult aspects of managing the spread and treatment of infected patients. In one study, it has been reported that roughly 50% of all new SARS-CoV-2 infections were estimated to have originated from asymptomatic individuals [4], which included both individuals who transmitted prior to the development of symptoms (42%) and individuals who never developed symptoms (8%) [4]. Studies such as these reinforced the unnerving truth that transmission between primary infections and secondary infections was just as likely to originate from a seemingly asymptomatic individual as a symptomatic individual. In the early stages of the pandemic, this inability to discern between infected and uninfected COVID-19 patients forced researchers and healthcare professionals around the world to collaborate and assess the potential for the initial epidemic of COVID-19 to evolve into a pandemic. To do so, researchers and healthcare professionals evaluated the risk of reaching a pandemic status through epidemiological studies, with various empirical techniques [5]. One of the best-established techniques for assessing risk is the reproduction number (R0).

As seen in **Figure** 1, R0 represents a well-established epidemiological concept that measures the potential for an infectious disease to spread by determining the average number of secondary infections that one primary case will generate [5]. Assuming nobody is either immune or vaccinated, an R0 value less than zero would represent the infections eventually stopping on their own, whereas an R0 greater than zero would estimate exponential growth in the number of cases in the given population. With R0 values averaging over 2.0 in most parts of the world, COVID-19 was expected to reach pandemic levels by the start of the second year [6]. Prior to December 2020 (when vaccines became mass-produced and widely distributed), SARS-CoV-2 was a global virus that would endure for many years to come. Without an accurate means of diagnosing individuals for SARS-CoV-2, there were no reliable means for quickly managing potential outbreaks and secondary infections. The high risk of lethality and seemingly permanent post-infection symptoms thus prompted urgent and necessary advancements in vaccine technology, but more importantly in diagnostic technology [1–4].

*Perspective Chapter: Microfluidic Technologies for On-Site Detection and Quantification… DOI: http://dx.doi.org/10.5772/intechopen.105950*

#### **Figure 1.**

*A schematic for visualizing the practical significance of R0 values. Adapted from Ref. [5].*
