Helicobacter pylori (H. pylori) infection remains a major public health problem, with an estimated prevalence of over 50% worldwide and 60-86% for Portugal. H. pylori is associated with significant morbidity and mortality from peptic ulcerative disease to gastric cancer, whose eradication therapy has proven to be effective in preventing these complications. Factors involved in the development of these conditions include H. pylori virulence, host genetic factors and gut microbiota. Given the increasing pattern of antibiotic resistance evidenced by this bacterium and the scarcity of available antibiotic therapy, both in Portugal and worldwide, there is not enough evidence on the best eradication strategy. Regarding the uncertainties about the potential negative impact of indiscriminate use of eradication therapy on gut microbiota, either by proton pump inhibitors or by antibiotics per se, there is an overriding need for evidence about the real impact of this therapy on oral or gut flora and possible clinical consequences in immunological, metabolic, nutritional and oncological terms.

Objectives: Comparative evaluation of the efficacy of the different quadruple therapy regimens recommended for the H. pylori eradication. Comparative evaluation of the safety profile in terms of clinical, and immunological and gut microbiota impact of the different therapies for the H. pylori eradication.

Introduction: Helicobacter pylori (H. pylori) infection remains a major public health problem, with an estimated prevalence of over 50% worldwide and 60-86% for Portugal. H. pylori is associated with significant morbidity and mortality from peptic ulcerative disease to gastric cancer, whose eradication therapy has proven to be effective in preventing these complications. Factors involved in the development of these conditions include H. pylori virulence, host genetic factors and gut microbiota. Given the increasing pattern of antibiotic resistance evidenced by this bacterium and the scarcity of available antibiotic therapy, both in Portugal and worldwide, there is not enough evidence on the best eradication strategy. Regarding the uncertainties about the potential negative impact of indiscriminate use of eradication therapy on gut microbiota, either by proton pump inhibitors or by antibiotics per se, there is an overriding need for evidence about the real impact of this therapy on oral or gut flora and possible clinical consequences in immunological, metabolic, nutritional and oncological terms.

Objectives: Comparative evaluation of the efficacy of the different quadruple therapy regimens recommended for the H. pylori eradication. Comparative evaluation of the safety profile in terms of clinical, and immunological and gut microbiota impact of the different therapies for the H. pylori eradication.

Methods: Prospective longitudinal multicentre study of total of patients with gastric infection by H. pylori, diagnosed by 13C-urea breath test or histological analysis of gastric biopsies and clinical indication for its eradication, referred to the different participating Portuguese hospital units and a blind randomized controlled clinical trial of the efficacy and safety of the different quadruple therapy regimes recommended for the H. pylori eradication. This study will be carried out in 4 phases: Phase 1 - Recruitment and randomization of patients by the different quadruple eradication schemes with and without bismuth (5 parallel arms); Phase 2 - H. pylori eradication with evaluation of the efficacy and safety rates at 1 month and the absence of reinfection at 12 months after treatment and collection of stool samples before and after the eradication therapy for evaluation of changes in gut microbiota; Phase 3 - Analysis of richness, diversity and uniformity of gut microbiota by DNA sequencing using the hypervariable region of the ribosomal 16S bacteria gene as a taxonomic identification marker and their clinical impact on immunology, metabolism and nutrition at 12 months after the H. pylori eradication therapy; and Phase 4 - Analysis of immunological changes through the study of cell populations by flow cytometry (CD4+, CD8+, B-cell, T-cell, natural killer cells, cells ratio) and cytokines, chemokines and growth factors by xMAP/Luminex before and 12 months after the H. pylori eradication therapy.

Expected results, impact and scientific outputs: Given the high rate of triple therapy inefficacy, high antibiotic resistance and the scarcity and controversy of existing literature on quadruple regimens, there may be relevant differences in the approved quadruple regimens for the H. pylori eradication, being necessary to define which is the most effective and safe in Portugal, decreasing the rate of ineffectiveness and exposure to multiple antibiotics. The homeostasis of gut microbiota is significantly changed after H. pylori eradication and this modification may be substantially different according to the therapeutic scheme used, with clinical implications on immunology, metabolism and nutrition. Thus, a randomized trial to compare quadruple regimens is need, allowing in the future, an individualized selection of the H. pylori eradication regimen, taking into account the higher efficacy and safety and lower gut dysbiosis and its systemic consequences, in short and long term. Modulating oral and gut microbiota therapies, including prebiotics, probiotics, symbiotics, fecal microbiota transplantation and perhaps targeted-immunotherapy may be beneficial as adjuvant therapy to existing H. pylori eradication regimens, in a systematic way or for some therapeutic regimes or risk groups.

Inclusion Criteria:

• Gastric infection by H. pylori by histological examination of gastric biopsies or carbon 13-labeled urea breath test.

Exclusion Criteria:

• Age < 18 years;
• Pregnant, breast-feeding or women of childbearing age who do not comply with effective anticonception measures;
• History of allergy, hypersensitivity or contraindication to the use of H. pylori eradication drugs (antibiotics or proton pump inhibitors);
• History of previous gastrointestinal surgery or neoplasia;
• Previous H. pylori eradication therapies; Antibiotic or probiotic therapies in the month prior to recruitment;
• Use of proton pump inhibitors, other antacids or gastric mucosal protection agents in the 2 weeks prior to recruitment;
• Corticosteroids or immunomodulatory therapy in the month prior to recruitment;
• Immunodeficiency;
• Insulin-treated diabetes mellitus;
• Obesity (Body mass index ≥30Kg/m2);
• Use of laxative therapy in the 15 days prior to recruitment;
• Decompensated heart, liver, kidney or respiratory diseases and;
• Refusal or inability to give informed consent.

No applicable.

Sampling: Consecutive sampling of incident cases of patients with H. pylori gastric infection and clinical indication for its eradication; Patients will be continuously monitored throughout the study. Regarding the evaluation of oral and gut microbiota and immunological changes, the study will be blinded, since the researchers responsible for sequencing and immunological analysis will not know the therapeutic scheme applied.