H. pylori: who is tested, how accurate the tests are, and what treatment has shown for stomach cancer

This article is for information only and does not replace a consultation with your doctor.

A line that reads "H. pylori: positive" on a breath-test or stool-test report tends to raise two questions at once. Is this the bacterium people link to stomach cancer? And if so, does treating it actually change anything, or is it one more test result that leads nowhere? Both questions have answers from trials: eradication has been tested against gastric-cancer outcomes in randomised trials, almost all of them in places where gastric cancer is common.

What is H. pylori, and how common is it?

Helicobacter pylori is a bacterium that lives in the lining of the stomach. A systematic review of 184 studies from 62 countries estimated that about 4.4 billion people carried it in 2015, with prevalence ranging from roughly 19% in Switzerland to 88% in Nigeria. The infection causes inflammation of the stomach lining (gastritis) whether or not there are symptoms; the prevalence review does not say how many carriers notice nothing. In some, it is linked to peptic ulcers and, over decades, to gastric cancer — which is why the question "treat or leave it" matters.

How is it tested, and how accurate are the tests?

There are three common non-invasive tests: a urea breath test, a stool antigen test and a blood antibody test (serology). A Cochrane review pooled 101 studies with 11,003 participants; most of the studies (57%) enrolled people with indigestion (dyspepsia). At a fixed specificity of 90%, sensitivity was about 94% for the carbon-13 breath test, 92% for the carbon-14 breath test, 84% for serology and 83% for the stool antigen test. In the review's illustration of 1,000 people tested, the carbon-13 breath test would miss about 30 infections, the carbon-14 breath test about 42, serology about 86 and the stool antigen test about 89; at that specificity each test would also give about 46 false positives.

Two caveats matter for your own result. First, many of the included studies excluded people who had recently taken acid-suppressing drugs (proton pump inhibitors) or antibiotics, and guidelines ask for these to be paused before breath and stool testing because they can produce a false negative. Second, blood antibodies can stay positive for months, and sometimes years, after the infection is gone, so a positive antibody test does not separate a current infection from a past one.

What did the trials show about stomach cancer?

The strongest evidence comes from randomised trials, almost all of them in East Asia, where gastric cancer is common.

• Infected adults without gastric cancer. A 2020 meta-analysis pooled seven trials with 8,323 people it classed as healthy infected adults. Fewer gastric cancers occurred after eradication therapy (relative risk 0.54) and fewer deaths from gastric cancer (relative risk 0.61). All-cause mortality did not differ. The authors rated the evidence as moderate. Six of the trials were in East Asia and one in a high-risk area of Colombia, and the authors describe the result as applying to East Asian countries.

• First-degree relatives of people with gastric cancer. In a Korean double-blind trial, 1,838 infected first-degree relatives were randomised and 1,676 analysed; over a median of 9.2 years, gastric cancer developed in 1.2% of the treated group and 2.7% of the placebo group. Mild side effects were more common with treatment (53% vs 19%).

• People who had an early cancer or a high-grade adenoma removed endoscopically. In a Korean trial, 470 such patients were randomised and 396 analysed; over a median of 5.9 years, a new gastric cancer developed in 7.2% after treatment and 13.4% after placebo.

• Long follow-up. In a Chinese trial in Linqu County, 2,258 residents with antibodies to H. pylori were assigned a two-week course or placebo in 1995, and that course was still associated with fewer gastric cancers 22 years later (odds ratio 0.48).

• Whole communities. A cluster-randomised trial in Linqu enrolled 180,284 people from 980 villages and followed them for 11.8 years. Among those who tested positive, the treated group had a modest reduction in gastric cancer (hazard ratio 0.86).

What do these results not say?

They do not show that every carrier will get cancer, or that treatment makes cancer impossible: in the family-history trial, five of the ten cancers in the treated group occurred in people whose infection persisted, and cancers still occurred after successful eradication. An earlier Chinese trial of 1,630 carriers found no overall difference over 7.5 years; the benefit appeared only in the subgroup without precancerous changes at the start. The European consensus says eradication is most effective before severe chronic atrophic gastritis develops and that the benefit is smaller at older ages — but older age is not a reason to withhold treatment.

The population matters too. These trials were done where gastric cancer is frequent. How large the effect is in lower-risk populations has not been measured in a trial of the same kind. The Matsu Islands programme in Taiwan reported fewer cancers after mass screening and treatment, but it compared the programme period with earlier years rather than with a randomised control group, so it is weaker evidence.

Why does treatment sometimes fail?

Antibiotic resistance. A meta-analysis of 178 studies covering 66,142 bacterial samples from 65 countries found resistance to clarithromycin, metronidazole and levofloxacin at 15% or more in most WHO regions, and clarithromycin resistance was strongly associated with failure of clarithromycin-containing regimens (odds ratio 6.97). This is why current European and American guidelines tie the choice of regimen to known or likely resistance and to what has already been tried — a choice the doctor makes. A negative breath or stool test taken at least four weeks after treatment is what confirms cure; the American guideline asks for this test after treatment.

What should you do with a positive result?

• A positive breath or stool test is what guidelines treat as evidence of a current infection — strong evidence rather than a certainty, since a small share of positives are false. Current European and American guidelines recommend treating confirmed infection; the regimen is chosen by the doctor, based on local resistance and your previous antibiotic use.

• After treatment, a repeat breath or stool test is the step that confirms the result. Without it, you do not know whether the course worked.

• If a parent, sibling or child has had gastric cancer, that matches the group in the Korean trial above — infected first-degree relatives — and is worth raising with your doctor even without symptoms.

• A positive blood antibody test alone is a reason to confirm with a breath or stool test, not a reason to start treatment on its own.

The European consensus suggests endoscopy with biopsies for people without symptoms who have a non-hereditary family history of gastric cancer from age 45, while noting there is no evidence for one exact starting age. Symptoms change that question further, and that part belongs with a gastroenterologist rather than with a single test result. For a wider view of which checks after 40 change outcomes, see Screening after 40: which tests change outcomes.

Sources

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