3.2. Clinical Symptoms
The initial symptoms of SARS patients were fever (100%), cough (61.8%), myalgia (48.7%), dyspnea (40.8%), and diarrhea (31.6%) [29], and the prognosis of patients was associated with host characteristics (including age, gender, etc.) [30]. During hospitalization, respiratory distress occurred in 90.8% of SARS patients [29]. The duration from disease onset to severe respiratory distress was an average of 9.8 ± 3.0 days [29]. During the disease course, some patients developed leukopenia, lymphopenia, and thrombocytopenia with an upregulation of aspartate transaminase (AST), alanine aminotransferase (ALT), lactic dehydrogenase (LDH), and C-reactive protein (CRP) [29].
In comparison, COVID-19 showed similar trends with SARS patients [28]. Fever, fatigue, and dry cough are the main manifestations of the patients, while nasal congestion, runny nose, and other symptoms of the upper respiratory tract are rare. Beijing Centers for Diseases Control and Prevention indicated that the typical case of COVID-19 has a progressive aggravation process. COVID-19 can be classified into light, normal, severe, and critical types based on the severity of the disease [31]: (1) Mild cases—the clinical symptoms were mild, and no pneumonia was found on the chest computed tomography (CT); (2) normal cases—fever, respiratory symptoms, and patients found to have imaging manifestations of pneumonia; (3) severe cases—one of the following three conditions: Respiratory distress, respiratory rate ≥ 30 times/min (in resting state, refers to oxygen saturation ≤ 93%), partial arterial oxygen pressure (PaO2)/oxygen absorption concentration (FiO2) ≤ 300 mmHg (1 mmHg = 0.133 kPa); (4) critical cases—one of the following three conditions: Respiratory failure and the need for mechanical ventilation, shock, or the associated failure of other organs requiring the intensive care unit [32]. The current clinical data shows that the majority of the deaths occurred in the older patients. However, severe cases have been documented in young adults who have unique factors, particularly those with chronic diseases, such as diabetes or hepatitis B. Those with a long-term use of hormones or immunosuppressants, and decreased immune function, are likely to get severely infected.