Selection criteria

Inclusion and exclusion criteria were defined prior to the literature search. Hence, the following criteria had to be met for studies to be included in this meta-analysis: 1) published as full articles or letters to the Editor; 2) written in English; and 3) cohort studies, with extractable data concerning the involvement of the digestive system in SARS-Cov-2 infection, including at least 15 patients. Exclusion criteria were the following: 1) studies not meeting the inclusion criteria; 2) studies without data for retrieval; 3) duplicate studies; and 4) the less informative publication of two on the same study. Concerning quality, the cohort studies included in this meta-analysis were assessed by using the Newcastle-Ottawa Quality Assessment Scale for cohort studies [14]. This scale assesses the main sources of bias, including the selection of study cohorts, comparability of cohorts, and outcome assessment. Furthermore, it uses a “star system” to judge a study on these three broad perspectives, with a maximum possible score of 9. According to the score, and therefore the relevant risk of bias, studies were classified as low, fair, and high quality.