Abstract
The scientific knowledge already attained regarding the way severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects human cells and the clinical manifestations and consequences for Coronavirus Disease 2019 (COVID-19) patients, especially the most severe cases, brought gut microbiota into the discussion. It has been suggested that intestinal microflora composition plays a role in this disease because of the following: (i) its relevance to an efficient immune system response; (ii) the fact that 5-10% of the patients present gastrointestinal symptoms; and (iii) because it is modulated by intestinal angiotensin-converting enzyme 2 (ACE2) (which is the virus receptor). In addition, it is known that the most severely affected patients (those who stay longer in hospital, who require intensive care, and who eventually die) are older people with pre-existing cardiovascular, metabolic, renal, and pulmonary diseases, the same people in which the prevalence of gut microflora dysbiosis is higher. The COVID-19 patients presenting poor outcomes are also those in which the immune system's hyperresponsiveness and a severe inflammatory condition (collectively referred as "cytokine storm") are particularly evident, and have been associated with impaired microbiota phenotype. In this article, we present the evidence existing thus far that may suggest an association between intestinal microbiota composition and the susceptibility of some patients to progress to severe stages of the disease.