Virological and histological evaluation of intestinal samples in COVID-19 patients.

Background: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the pathogen responsible for pandemic coronavirus disease 2019 (COVID-19). It is a highly contagious virus which primarily affects the respiratory tract, nevertheless, the lungs are not the only target organs of the virus. The intestinal tract could represent an additional tropism site for SARS-CoV-2. Several observations have collectively suggested that enteric infections can occur in COVID-19 patients. However, the detection of viral RNA in gastrointestinal (GI) tissue samples has not been adequately investigated and results are conflicting.

Aim: To detect the presence of SARS-CoV-2 RNA in intestinal mucosa samples and to evaluate histological features.

Methods: The COVID-19 patients hospitalized at an Italian tertiary hospital from April 2020 to March 2021 were evaluated for enrollment in an observational, monocentric trial. The study population was composed of two groups of adult patients. In the first group (biopsy group, 30 patients), patients were eligible for inclusion if they had mild to moderate disease and if they agreed to have a rectal biopsy; in the second group (surgical specimen group, 6 patients), patients were eligible for inclusion if they underwent intestinal resection during index hospitalization. Fifty-nine intestinal mucosal samples were analyzed.

Results: Viral RNA was not detectable in any of the rectal biopsies performed (0/53). Histological examination showed no enterocyte damage, but slight edema of the lamina propria with mild inflammatory lymphoplasmacytic infiltration. There was no difference in inflammatory infiltrates in patients with and without GI symptoms. SARS-CoV-2 RNA was detected in fecal samples in 6 cases out of 14 cases examined (42.9%). In the surgical specimen group, all patients underwent emergency intestinal resection. Viral RNA was detected in 2 surgical specimens of the 6 examined, both of which were from patients with active neoplastic disease. Histological examination also pointed out abundant macrophages, granulocytes and plasma cells infiltrating the muscular layer and adipose tissue, and focal vasculitis.

Conclusion: Mild-moderate COVID-19 may not be associated with rectal infection by the virus. More comprehensive autopsies or surgical specimens are needed to provide histological evidence of intestinal infection.