**1. Introduction**

For over 2 years from its emergence, the coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 500 million cases and 6.2 million deaths worldwide as of May 2022 [1]. This highly contagious disease spreads through the respiratory tract via sneezing, coughing, and talking and causes a range of symptoms from mild, like coughing, to severe, like pneumonia. Most patients are asymptomatic and do not require hospitalization; however, high-risk groups—elders over 65 years old, patients with obesity, impaired immune system, and chronic diseases—may develop serious complications that lead to septic shock, multi-organ failure, and eventually, death. However, asymptomatic patients are 75% more likely to spread the disease to others

compared to symptomatic cases, which hinders the control of this pandemic [2–5]. It overtook both SARS and MERS outbreaks in terms of infectivity and spread [6]. This crisis still poses a threat to public health and socioeconomics globally ever since its appearance in late 2019. SARS-CoV-2 is from a family of viruses that undergo frequent mutations that alter its characteristics like infectiousness and the rate of transmission.

To control the spread of the pandemic, expanded and rapid point of care (POC) testing is of utmost importance. The reverse transcription-quantitative polymerase chain reaction (RT-qPCR) molecular testing is the gold standard according to world health organization (WHO). This bulky and expensive instrument requires special facilities and must be operated by experts, which makes expanded testing challenging in resource-poor regions. Alternative testing methods are needed for simple and fast POC testing to resolve the demand for reagents and diagnostic equipment in such regions. Therefore, fast, affordable, and practical alternative diagnostic tests to detect the novel SARS-CoV-2 are being investigated, one of which meets these criteria is the loop-mediated isothermal amplification (LAMP). LAMP is a molecular test that provides simple detection methods including the colorimetric LAMP, which relies on a color change in the presence of viral nucleic acids and can be detected via the naked eye. Addition of reverse transcriptase (RT-LAMP) enables the detection of RNA pathogens in a one tube reaction. This single-step technique does not require sophisticated equipment, as the reaction takes place isothermally. This chapter summarizes the most recent developments on the colorimetric RT-LAMP assay for the diagnosis of COVID-19.
