# COVID-19 Diagnosis from Crowdsourced Cough Sound Data
## 1 Introduction  
COVID-19, a disease caused by the coronavirus SARS-CoV-2, was declared a pandemic by the World Health Organization (WHO, Geneva, Switzerland) on 11 March 2020. The virus is spread in the form of small particles expelled from the mouth or nose when an infected person coughs, sneezes, speaks, sings, or breathes. These particles take various forms, from respiratory droplets to aerosols. Therefore, individuals adjacent to a person infected with the COVID-19 virus, or who touch the eyes, nose, or mouth with hands that have come into contact with contaminated surfaces, may get infected. The infection therefore spreads more easily indoors or in crowded places. The symptoms of COVID-19 range from none to mild, moderate, or severe, with major symptoms including fever of 37.5 \({}^{\circ}\)C or higher, fatigue and cough, and dyspnea (shortness of breath), while other symptoms include chills, muscle pain, headache, and olfactory, or taste loss. Other symptoms, such as loss of appetite, production of phlegm, digestive symptoms, confusion, dizziness, runny nose, or stuffy nose may occur. For most people, symptoms are mild. However, in some people, the virus affects the respiratory system and changes the quality of voice, coughing sound, and breathing sound. The trend of COVID-19 confirmed patients around the world is shown in Figure 1.  
As shown in Figure 1, the total number of confirmed infections worldwide is about 250 million, and the death toll is about 5.1 million. As the number of confirmed cases increases, the number of patients who have recovered is increasing, but there have been many deaths. Many epidemiological experts argue that a large-scale coronavirus testing is essential. Reverse transcription-polymerase chain reaction (RT-PCR), which is currently used all over the world, is currently the standard approach to diagnosing COVID-19 with high accuracy [2]. The RT-PCR test is reliable, but the process of collecting a sample using a long swab in the nose can be painful, and is costly to the individual in some countries [3]. Rapid diagnosis is also difficult, because the test results can be received within a few hours toa few days after the test. With the advent of the new virus, many experts are uncertain as to when herd immunity will be reached. There are four recently developed vaccines: AstraZeneca, Janssen, Pfizer, and Moderna. Vaccination helps protect individuals from COVID-19. Vaccination is recommended at the national level, and many people in South Korea have been vaccinated (Figure 2). As shown in Figure 2, more and more people have been vaccinated over time, and some experience side effects from the vaccines. Side effects may affect the ability to perform daily activities. They may disappear within a few days, or cause an allergic reaction. Notably, vaccine-associated adverse reactions were more commonly reported in the AstraZeneca vaccination group than in the Pfizer vaccination group [4]. Above all, with the advent of new strains and breakthrough infections, many experts are uncertain as to when herd immunity can be reached. Rapid and scalable diagnostic testing technologies are required to solve this problem. Research into diagnostic test technology has been actively conducted in many fields. The fact that the COVID-19 virus affects the human lungs has made it possible to study diagnostic testing techniques in a variety of ways. Studies have been conducted to distinguish between the lungs of COVID-19 positive people and the lungs of healthy people using lung CT scans and X-rays. These studies have more than 90% accuracy, and the results are constantly improving [5; 6]. Diagnostic test studies using artificial intelligence (AI) to interpret audio signals generated from the human body, such as cough sounds, are ongoing [7; 8; 9; 10; 11; 12; 13; 14; 15]. The flowchart of the basic diagnostic process is shown in Figure 3.  
As shown in Figure 3, cough sound data is generally collected using crowdsourcing.