**1. Main Text**

At the time of writing this letter, the principal cause of mortality in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is respiratory failure with exudative diffuse alveolar damage and massive capillary congestion often accompanied by microthrombi or, in lower percentages, by generalized thrombotic microangiopathy, as reported by post-mortem examinations [1]. With coronavirus infectious disease 2019 (COVID-19) being conceived as a solely respiratory disease [2,3],

**Mauro Giu**ff**rè 1,2,\*, Stefano Di Bella 1, Gianluca Sambataro 3, Verena Zerbato 4, Marco Cavallaro 5, Alessandro Agostino Occhipinti 6, Andrea Palermo 7, Anna Crescenzi 8, Fabio Monica 9, Roberto Luzzati 1 and Lory Saveria Crocè 1,2**

the scientific community initially assumed that the lungs represented the preferred and initial site of viral proliferation, as well as its primary source for shedding and transmission.

#### **2. Gastrointestinal Manifestations of COVID-19**

Recent findings indicated that SARS-CoV-2 could bind to gastrointestinal cells via specific receptors (such as the angiotensin converting enzyme-2 (ACE2) receptor and the transmembrane serine protease 2) [4], whose interaction is supposed to promote local inflammation by massive cytokine and chemokine release [5]. Additionally, an autoptic study on the small intestine of two COVID-19 patients showed endotheliitis of the submucosa vessels and evidence of direct viral infection of endothelial cells [6].

Regarding the clinical presentation, gastrointestinal symptoms are present in up to 28% of patients with COVID-19 [7–9], and fecal SARS-CoV-2-RNA was detected in approximately 50% of positive individuals [8–10]. Recently, E ffenberger et al. [5] proposed the role of fecal calprotectin (FC) as a marker of intestinal inflammation in COVID-19 patients who developed gastrointestinal (GI) symptoms. In particular, the authors detected significantly higher FC values in patients with acute diarrhea if compared to patients without diarrhea or with ceased diarrhea (>48 h). In this pilot study, we aimed to externally validate the results of E ffenberger et al. [5] by determining the actual absence of significant FC concentrations in patients who did not present gastrointestinal symptoms and without previous history of inflammatory bowel disease (IBD).

#### **3. Materials and Methods**

We performed a prospective observational cross-sectional study by enrolling 25 consecutive COVID-19 inpatients from May 2020 to June 2020, who were admitted without gastrointestinal symptoms and a previous history of IBD.

SARS-CoV-2 detection in nasopharyngeal swabs was determined by PCR (LightMix ®- Modular-Wuhan CoV-RdRP and E genes). FC concentration was determined by the DiaSorin-LIAISON ®-Calprotectin according to the manufacturer's specification (normal range <50 mg/kg). Both tests were performed at admission. Potential infective causes for FC increase were investigated through canonical stool analysis for common bacteria, viral and parasitic pathogens.

Data were displayed as median (Quartile 1; Quartile 3). We explored the correlation between continuous variables via Spearman's correlation coe fficient, considering a statistically significant two-tailed *p*-value < 0.05.
