More than half the world’s population is walking around with a bacteria that can cause stomach cancer and ulcers.

It could be as many as three out of four people are infected.

Most of them have no idea, nor do they have symptoms – which is a little odd.

It’s not fully understood why and how the bacterium Helicobacter pylori is spread.

It’s thought to be passed from person to person through direct contact with saliva, vomit or faeces. It may also be spread through contaminated food or water.

According to the federal government’s Health Direct advice, H. pylori is “mostly transmitted through close contact with family members, or in day care centres. Better hygiene has helped reduce H. pylori in developing countries”.

In Australia, where we have abundant clean drinking water, and the means to maintain good hygiene, it’s thought that about a third of the population carries the infection.

Another mystery is what triggers or allows Helicobacter pylori to graduate from harmless freeloader to a dangerous one.

A 2014 study found that H. pylori “rapidly identifies and colonises sites of minor injuries in the stomach”.

This almost immediately interferes with healing at those injury sites, “and so promotes sustained gastric damage”.

These minor injuries can easily come from diet, medicines or caustic ingredients used in manufacturing illegal drugs.

How it thrives

The bacterium Helicobacter pylori lives in the mucus layer of the stomach lining and duodenum.

The bugs secrete an enzyme called urease that converts urea to ammonia.

It’s this ammonia that protects the bacteria from stomach acid.

As H. pylori multiply, it eats into stomach tissue, which leads to gastritis.

Gastritis is a fancy word for inflammation of the stomach wall. It can be caused by things other than H. pylori such as over-the-counter ibuprofen.

Mild gastritis is unlikely to do you much harm, can go unnoticed, and – if H. pylori isn’t present, and therefore not a factor – can be managed with a change in diet.

Spicy or acidic foods like garlic, mustard and pepper can all have a negative effect on people with H. pylori infections so it is best to avoid them.

High-fat foods. Fatty foods like fatty meats and fried foods can make digestion slow down, causing foods to stay in the stomach longer, worsening symptoms.

It’s when H. pylori progresses from gastritis to causing open sores in the stomach (gastric ulcers), or in the upper part of the small intestine (duodenal ulcers). that you should notice you’ve got a problem.

Common symptoms

If you have symptoms, they may include:

• Dull or burning pain in your stomach (more often a few hours after eating and at night). Your pain may last minutes to hours and may come and go over several days to weeks
• Unplanned weight loss
• Bloating
• Nausea and vomiting (bloody vomit)
• Indigestion (dyspepsia)
• Burping
• Loss of appetite
• Dark stools (from blood in your stool).

Diagnosis and treatment

The most common symptom is intermittent burning pain in the stomach.

Don’t just go to a chemist and get some antacids.

Any persistent pain needs to be properly checked, and doubly so if it’s in your organs.

That pain is Helicobacter pylori, which you’ve probably carried since childhood, finally making itself known.

From there, diagnosis and treatment are relatively straightforward.

The simplest way to diagnose Helicobacter pylori is with a breath test. It may turn up in a blood test, stool sample or endoscopy with tissue biopsy of the stomach lining.

The infection is treated with eradication therapy – a combination of medicines that includes antibiotics (kills the bacteria) and acid-suppressing medicine (allows the sores to heal).

Sometimes, the first treatment doesn’t work because the bacteria aren’t affected by the antibiotics.

This is a consequence of antibiotic resistance. In this case, a specialist gastroenterologist may prescribe different medicines.

Once H. pylori is successfully treated, your risk of getting infected again is low.