H. pylori: The Bacterium Behind Most Stomach Ulcers

Helicobacter pylori is the most successful bacterial colonizer of human beings. Something close to half the world carries it in the stomach, most people acquire it in childhood, and the overwhelming majority never know and never suffer for it.

It is also the cause of most stomach and duodenal ulcers, and a recognized risk factor for stomach cancer. Those two facts sit together uncomfortably, and they explain why it is treated when it is found rather than watched.

It is unusual among the infections covered on this site in that most carriers need nothing at all, which puts it closer to latent tuberculosis than to an acute illness: a dormant finding, treated because of what it might do rather than because of how it feels.

What it does, and to whom

The bacterium survives in the stomach by neutralising acid immediately around itself and burrowing into the mucus lining. That provokes inflammation, which in most people causes nothing detectable for a lifetime.

What happens to people who carry it

Outcome	Roughly how often	What it means
Nothing at all	The large majority	No symptoms, no consequence
Chronic gastritis	Very common, often silent	Inflammation without symptoms
Peptic ulcer	Around one in ten carriers	Pain, sometimes bleeding; curable by eradication
Stomach cancer	A small minority	The reason eradication is recommended when found
MALT lymphoma	Rare	Can sometimes resolve with eradication alone

That fourth row carries most of the weight in the decision to treat. The individual risk is low; the population effect is large enough that eradication is recommended for everyone found to carry it.

Who gets tested

Testing is not universal, which surprises people. It is directed at those in whom finding it would change something.

• Anyone with a current or previous peptic ulcer
• Persistent indigestion, particularly under sixty and without alarm features
• People starting long-term aspirin or anti-inflammatory drugs, in some guidance
• Anyone with a first-degree relative who has had stomach cancer
• Unexplained iron deficiency anemia, once other causes are excluded
• Certain blood disorders, notably immune thrombocytopenia
• Following treatment, to confirm it worked

How people get it, and whether the household needs testing

Transmission is person to person, mostly within households and mostly in childhood, by the oral and fecal-oral routes. Crowded living conditions and poor sanitation in early life raise the likelihood considerably, which is why prevalence varies so much between countries and generations.

Family members are not routinely tested when one person is found to carry it. The exception is a household where someone has had stomach cancer, where testing relatives is reasonable. Otherwise the usual guidance is to test people who have a reason to be tested, not everyone who lives with them.

Reinfection after successful treatment is uncommon in adults in countries like the United States — a few percent per year at most. A positive test years later more often means the original treatment failed than that it was caught again, which is part of why confirming eradication matters.

How it is tested for

• Urea breath test — accurate, non-invasive, and the usual choice
• Stool antigen test — equally reasonable, and often more practical
• Endoscopy with biopsy — where the lining needs examining, or where resistance testing is wanted
• Blood antibody tests — largely abandoned, because they stay positive after successful treatment and cannot distinguish past from present

One practical trap: acid-suppressing medication and recent antibiotics both make the breath and stool tests falsely negative. Proton pump inhibitors are usually stopped two weeks before, and antibiotics four weeks before.

What it is not

H. pylori is blamed for a good deal it does not cause, partly because it is easy to test for and partly because a positive result feels like an answer.

• It is not the cause of most indigestion; functional dyspepsia is commoner and eradication helps only a minority
• It is not a cause of reflux, and treating it does not improve heartburn
• It does not cause the vague fatigue and bloating it is sometimes blamed for
• It is not a reason to avoid particular foods; diet does not eradicate it
• It is not transmitted casually between adults in the way a respiratory virus is
• A positive test in someone with an unrelated problem does not explain that problem

Where indigestion persists after successful eradication, the answer usually lies elsewhere, and continuing to look at the stomach is not always the right move. That is a conversation worth having explicitly rather than by repeated testing.

Treatment: several medicines at once, for a reason

Eradication requires combination therapy — usually two antibiotics plus an acid-suppressing drug, sometimes with bismuth, for fourteen days. It is a lot of tablets and it is not negotiable down to one or two: single agents fail almost completely.

Resistance has made this harder than it used to be. Clarithromycin resistance in particular has risen to the point that the old standard regimen fails often enough to have been displaced in much guidance. Our article on antibiotic resistance explains the mechanism, and how long antibiotic courses run explains why the fourteen days matter.

• Take every dose; partial treatment is the main driver of failure, for the reasons in our article on how long antibiotic courses run
• Expect side effects — a metallic taste, nausea, loose stools are all common
• Avoid alcohol entirely if the regimen includes metronidazole; see antibiotics and your other medicines
• Tell the prescriber every antibiotic you have taken in recent years, because previous exposure guides the choice
• Check interactions, particularly with other medicines; see antibiotics and your other medicines
• Do not stop early because you feel better; there is nothing to feel

The retest, which is the part most often skipped

Treatment fails in a meaningful proportion of people, and because most carriers have no symptoms, failure is invisible. Confirming eradication is therefore standard: a breath or stool test at least four weeks after finishing antibiotics, and at least two weeks after stopping acid suppression.

Diarrhea during the course is common and is usually a nuisance rather than a problem, but severe or bloody diarrhea needs reporting; our article on C. difficile after antibiotics covers why.

If the first course fails, a second is chosen using different antibiotics rather than repeating the same ones. Repeated failure is where a gastroenterology or infectious disease opinion is genuinely useful, and where testing the organism for resistance starts to be worth doing.

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