H. pylori Wrecks Kids’ Stomach Microbiome Even Without an Ulcer, Study Finds

If your child has had months of stomach pain, nausea, or unexplained appetite loss and an endoscopy came back clear of ulcers, doctors may have told you there's nothing urgent to treat, even if a test came back positive for Helicobacter pylori (H. pylori, a spiral bacterium that colonizes the stomach lining). Current pediatric guidelines generally hold off on antibiotic eradication in that exact scenario. A new prospective study of 120 children and teens in Chile now shows that "nothing urgent" may not mean "nothing happening": kids infected with H. pylori who never developed an ulcer still had a stomach microbiome in visible disarray, and the degree of disruption tracked directly with how much inflammation their stomach lining showed under the microscope.

Key takeaways

• Among 120 symptomatic children and teens (ages 8-20) who underwent endoscopy, the 41 who tested positive for H. pylori had significantly lower gut microbial diversity than the 79 who tested negative, with H. pylori itself dominating their stomach bacterial community.
• The severity of this dysbiosis (microbial imbalance) rose step-wise with histological gastritis grade, independent of the child's age, puberty stage, or sex.
• The senior authors argue this supports reconsidering pediatric guidelines that currently withhold eradication therapy in symptomatic, ulcer-free H. pylori cases.
• The big caveat: this is an association, not a trial proving eradication improves outcomes, and it comes from a single country's hospital network with 41 infected children.

H. pylori Reshapes the Gastric Microbiome Even Without Ulcers

Children and teens infected with H. pylori but free of peptic ulcer disease (PUD, erosive damage to the stomach or duodenal lining) showed a stomach microbiome that looked structurally different from their uninfected peers, according to the study, published in Frontiers in Microbiology. Using 16S rRNA gene sequencing (a DNA-based technique that identifies which bacterial species are present in a tissue sample), researchers found that H. pylori-positive stomachs had lower species richness, lower evenness (how equally abundant different species are), and a "dominance index" driven almost entirely by H. pylori itself crowding out other microbes. Compositionally, the infected group showed decreased Firmicutes and Bacteroidota (two bacterial phyla typically associated with a balanced gut) alongside increased Proteobacteria and Campylobacterota, the phylum H. pylori itself belongs to. A statistical test of overall community structure (PERMANOVA) confirmed the two groups' microbiomes were significantly distinct (p = 0.001), and the split held up across ten phyla and 47 species that differed at nominally significant levels between groups.

Why This Matters for Symptomatic Kids Without an Ulcer Diagnosis

This finding lands squarely on a population that current guidance treats as low-priority: symptomatic children and adolescents with dyspepsia or abdominal pain who test positive for H. pylori but show no ulcer on endoscopy. The updated 2023 ESPGHAN/NASPGHAN guidelines for pediatric H. pylori management generally do not recommend a "test and treat" approach or routine eradication in this exact group, reasoning that infection alone doesn't reliably explain symptoms absent ulcer disease. The new data complicate that reasoning: even without an ulcer, these kids' stomachs are hosting a demonstrably altered, H. pylori-dominated microbial community, and (as this study adds) one that correlates with more severe inflammation. Gut and gastric dysbiosis in children has separately been linked to metabolic, cardiovascular, and neurological conditions that often don't surface until adolescence or adulthood, which is part of why the authors frame early, unresolved dysbiosis as a potential long-game concern rather than only an immediate one.

A Five-Hospital, Prospective Design Built for Real Clinical Relevance

The strength of the study is its design. Researchers prospectively enrolled 120 patients aged 8 to 20 undergoing upper gastrointestinal endoscopy for dyspepsia or abdominal pain across five tertiary hospitals in Santiago, Chile, between October 2019 and January 2023, rather than pulling from a single clinic or retrospectively mining charts. They excluded children on recent acid-suppressing medication or antibiotics, with active bleeding, or with confounding diagnoses like celiac disease or inflammatory bowel disease, which helps isolate H. pylori's own signal. Of the 120, 41 tested H. pylori-positive and 79 tested negative; every biopsy was independently graded for histological gastritis severity by pathology alongside the microbiome sequencing, and researchers also genotyped H. pylori virulence factors (CagA and vacA, two proteins linked to more aggressive strains) to see whether particularly dangerous strains explained more of the dysbiosis.

What a Parent or Patient Should Actually Take From This

If your child has tested positive for H. pylori and has symptoms but no ulcer, this study is not evidence that you should independently seek antibiotics; it's evidence that the "watch and wait" default deserves an informed conversation with a pediatric gastroenterologist rather than being treated as a closed question. The study found that dysbiosis severity rose in clear steps with gastritis grade: children with no gastritis had the least disrupted microbiome, those with mild gastritis were in between, and those with moderate-to-severe gastritis (36 children) showed the most distinct microbial profiles, with three co-occurring "marker" bacterial species distinguishing the severe cases. That's a meaningful signal for a doctor weighing eradication, but the study did not test whether treating the infection reverses the dysbiosis or reduces later disease risk, so no one should read this as license to self-treat or demand antibiotics without a clinician's evaluation.

Limitations: Association, Not a Treatment Trial, and Virulence Factors Muddy the Picture

The authors are explicit that this is an associational, cross-sectional look at 41 infected children, not a randomized trial of eradication versus no treatment, so it cannot prove that treating H. pylori earlier prevents downstream harm. It's also a single-country cohort from Chile, where H. pylori prevalence in symptomatic children reaches 30-40%, a much higher baseline than in many wealthier countries, which may limit how directly the findings generalize elsewhere. Virulence genotyping added a wrinkle rather than clean confirmation: the more aggressive CagA-positive strain (found in 55% of infected patients) was associated with a distinct microbiota profile (p = 0.019) but was not significantly associated with how severe the gastritis actually was (p = 0.211), and the other major virulence marker, vacA, showed no significant microbiota association at all (p = 0.187). In other words, strain aggressiveness alone doesn't cleanly predict who ends up with the worst inflammation, leaving open exactly which bacterial or host factors push some kids toward more severe gastritis than others.

What Comes Next for Guidelines and Follow-Up Research

The authors frame their results as a direct challenge to age-based eradication thresholds in pediatric guidelines, arguing that withholding treatment until a child is older, or until an ulcer appears, may allow dysbiosis and inflammation to persist unnecessarily. That's the authors' policy recommendation, not a change professional societies have adopted. Larger, multi-country cohorts, and ideally trials that track whether eradication in non-ulcer symptomatic children actually resolves the dysbiosis and gastritis over time, would be the next logical step; a related 2025 systematic review of H. pylori eradication's effects on gut microbiota underscores how unsettled that treatment-response question still is even in adults. Until such trials exist, this study's main practical contribution is sharpening the clinical debate rather than settling it.

Common Questions

Does this mean all kids with H. pylori should be treated with antibiotics? No. The study shows an association between infection, gastric dysbiosis, and gastritis severity in symptomatic children without ulcers; it did not test whether eradication treatment improves outcomes, so current guidelines have not changed based on this single study.

What is gastric dysbiosis, in plain terms? It refers to an imbalance in the community of bacteria normally living in the stomach, here marked by lower diversity, fewer species, and H. pylori dominating the community at the expense of bacteria like Firmicutes and Bacteroidota that are typically present in a balanced gut.

Why don't current guidelines recommend treating H. pylori in symptomatic kids without ulcers? Because prior evidence suggested the infection alone doesn't reliably explain symptoms when there's no ulcer, so international pediatric groups have prioritized invasive testing and treatment for children who do show ulcer disease rather than routine "test and treat."

Is this the first study to look at this specific group? The authors state it is the first study to specifically compare gastric microbiota in symptomatic, ulcer-free H. pylori-positive children and adolescents against uninfected symptomatic controls, rather than comparing infected children who already have peptic ulcer disease.

References

1. Dinka Ivulic, Camila Cabrera, Felipe Del Canto, et al. (2026). Gastric dysbiosis and more severe histological gastritis in symptomatic Helicobacter pylori-infected children and adolescents without ulcers: time to rethink early eradication?. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2026.1927606
2. Matjaž Homan, Nicola L. Jones, Patrick Bontems, et al. (2024). Updated joint ESPGHAN/NASPGHAN guidelines for management of Helicobacter pylori infection in children and adolescents (2023). Journal of Pediatric Gastroenterology and Nutrition. https://doi.org/10.1002/jpn3.12314
3. Alia Albush, Fayez Yassine, Hassan Abbas, Aya Hanna, Esber Saba, Melhem Bilen (2025). The impact of Helicobacter pylori infection and eradication therapies on gut microbiota: a systematic review of microbial dysbiosis and its implications in gastric carcinogenesis. Frontiers in Cellular and Infection Microbiology. https://doi.org/10.3389/fcimb.2025.1592977