In contrast to mild COVID-19 patients, the gut microbiota of patients with moderate and severe symptoms have been found to be of: (a) lower Firmicutes/Bacteroidetes ratio; (b) higher abundance of Proteobacteria; and (c) lower abundance Roseburia and Lachnospira. It has also been demonstrated that the lower Shannon diversity index (odds ratio (OR) = 2.85, 95% CI = 1.09–7.41, p = 0.032) and higher (≥96.8 mg/L) C-reactive protein (OR = 3.45, 95% CI = 1.33–8.91, p = 0.011) were predictors of severe COVID-19 (a score of 6 or higher in the WHO Clinical Progression Scale). The gene discussed is CRP; the disease is COVID-19.