Severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) and the associated coronavirus disease 2019 (COVID-19) have been spreading all around the world for past 3 years. Some of these convalescent individuals experienced long- term sequelae termed 'long COVID', or 'post- acute COVID-19 syndrome'(PACS). Common manifestations are systemic, neuropsychiatric, cardio- respiratory and gastrointestinal [1].

The prevalence of gastrointestinal PACS was 2-5% in different literatures [2][3]. The risk factors of gastrointestinal PACS include anosmia, ageusia, and presence of chronic bowel disease, dyspeptic symptoms and the psychological comorbidity [4]. Previous articles have discussed pathogenesis of PACS, which was associated with increasing serum cytokine level and persisted inflammatory status [5]. Whereas, the influence of chronic inflammation to target organ has not been well studied. Liu et al explored the gut microbiota dynamics in patients with PACS, which revealed higher levels of Ruminococcus gnavus, Bacteroides vulgatus and lower levels of Faecalibacterium prausnitzii [6]. Another article established the association between multisystem inflammatory syndrome in children (MIS-C) and zonulin-dependent loss of gut mucosal barrier [7]. According to previous studies, infectious enteritis may cause subsequent post infectious irritable bowel syndrome [8][9], which was associated with increased gut permeability, T-lymphocyte, Mast cell and proinflammatory cytokine [10][11]. It is reasonable that gastrointestinal PACS might be also associated with dysfunction of gut mucosal barrier.

Confocal laser endomicroscopy (CLE) is a new endoscopic imaging tool that enables visualization of gut mucosa changes. The gut permeability could be accessed by CLE in patient with irritable bowel syndrome [12]. This study aimed to explore the association between gut permeability and gastrointestinal PACS.

Inclusion Criteria:

• persisted gastrointestinal symptoms such as dyspepsia, abdomen pain, diarrhea or constipation 3 months after COVID-19 infection

Exclusion Criteria:

• Terminal cancer, surgical history of gastrointestinal tract, acute gastrointestinal tract bleeding, allergy to fluorescein, pregnant or breast feeding, helicobacter pylori infection, major cardiopulmonary disease, liver cirrhosis, end stage renal disease, autoimmune disease, inflammtory bowel disease, small intestinal bacterial overgrowth, celiac disease, type 1 diabetic mellitus, type II diabetic mellitus, gastroenteritis in 3 months, history of irritable bowel syndrome, usage of NSAID, steroid

persisted gastrointestinal symptoms such as dyspepsia, abdomen pain, diarrhea or constipation 3 months after COVID-19 infection