From asymptomatic to critical illness: decoding various clinical stages of COVID-19

The clinical course of COVID-19 is variable, with clinical manifestation ranging from 81% mild course to 14% severe course along with 5% critical course in patients. The asymptomatic course is reported to potentially range between 20% and 70% (avg. 33%). A more severe course is seen in the elderly, those with various chronic diseases, and the immunosuppressed, where the case fatality rate is higher in these risk groups. The disease progresses with various symptoms, such as fever, cough, shortness of breath, malaise, myalgia, taste and smell disorders, diarrhea, sore throat, headache, and conjunctivitis. The disease begins with shortness of breath, indicative of lung damage, after an average of 7 to 10 days, and progresses in ARDS, sepsis, and septic shock. Some patients quickly enter shortness of breath, while others gradually develop shortness of breath and chest tightness and burning. The risk factors for a poor prognosis are age, comorbidities, and changes in laboratory tests. Secondary bacterial and fungal infections frequently develop with steroids and immunosuppressants, especially in the intensive care unit. Frequent complications in hospitalized patients include pneumonia (75%), ARDS (15%), acute renal failure (9%), and acute liver injury (19%). An increased incidence of heart damage is observed, including acute heart failure, arrhythmias, and myocarditis. Of the patients hospitalized due to COVID-19, 10%–25% present with prothrombotic coagulopathy, resulting in venous and arterial thromboembolic events. The most common extrapulmonary symptom is neuropsychiatric involvement, frequently accompanied by insomnia, an impediment to remembering, and an altered state of consciousness. During the course of COVID-19, patients undergo some pathological changes (severe lymphopenia, high levels of C-reactive protein, D-dimer, ferritin, etc.) depending on the condition and exposure level of the affected systems as shown by various laboratory tests. The relevant tests are the guiding elements of risk assessment, clinical monitoring, disease severity, and prognosis setting and therapy decision-making processes.