The group one carcinogen lurking in Kiwi tummies and why NZ doesn’t screen for it

A tenacious bacterium has outlasted the stomach’s acid for thousands of years, mostly unnoticed. Finding and treating it could save hundreds of Kiwi lives. Mike Scott reports.

The human stomach is a pot of acid and enzymes churning and killing most of what you swallow.

For almost all microbes it is a Venusian hellscape, but not for Helicobacter pylori – a cancer-causing bacterium sublimely surviving in almost half the world’s population thanks to masterful evolution.

Over thousands of years, H. pylori, as it is commonly known, has perfected a three-part trick.

It converts urea in the stomach into ammonia, wrapping itself in a defensive cloud that neutralises acid around it.

Then, using whip-like flagella, it swims through the stomach’s mucus lining, using it like a blanket pulled overhead.

Once through, it anchors to the stomach wall and stays, lives and multiplies.

Most who carry it never know they have it, but for others it causes gastritis and ulcers.

But most concerning, it is behind about three-quarters of stomach cancers worldwide.

In 1994, the World Health Organisation (WHO) classified it as a group one carcinogen – the same category as tobacco and asbestos.

It is a discriminate killer.

Within the Kiwi population, it harms Māori and Pasifika at a far higher rate than Europeans.

In 2020, the Ministry of Health’s Cancer Action Plan put H. pylori on a shortlist of three cancers worth screening for, alongside lung and prostate.

Despite the intention, six years later no programme exists, and current detection of H. pylori in Kiwis is described as “opportunistic”.

While New Zealand waits for a screening programme, this common and largely unknown bacterium survives the stomach’s soupy acid, biding its time and, for some, killing.

The nastiness of stomach cancer

Poasa (Paul) Misipeka, 84, with his wife Nola, had half his stomach removed after being diagnosed with stomach cancer and is now slowly regaining his strength. Photo / Michael Craig

Paul Misipeka, 84, reckons he’s one of the lucky ones – see if you agree.

In 2024, while tinkering in his beloved garden at his Warkworth home, he felt unwell.

He struggled inside and fell asleep. His wife, Nola, was concerned and called an ambulance.

This was Misipeka’s first trip to hospital. He was checked out and sent home. Sadly, over the next weeks his condition worsened and he returned to hospital.

“I was really sick ... I was vomiting blood,” Misipeka, who hails from Niue, says.

An endoscopy found a tumour in his stomach – he had cancer.

As far as killer cancers go, stomach – or gastric – cancer is right up there.

It is the fifth most common cancer in the world and the fifth most common cause of cancer death, Dr Cameron Schauer, a gastroenterologist and clinical senior lecturer at the University of Auckland, says.

In New Zealand, about 400 people are diagnosed with stomach cancer each year and around 270 die from it, according to the Gut Cancer Foundation.

“And we don’t pick it up early enough,” he says.

Schauer led a major study of gastric cancer covering 21 years of cases, analysing 1797 patients, the largest of its kind done in New Zealand.

“The vast majority of cases that we had, in fact more than 84% of cases, were very advanced.”

Dr Cameron Schauer, of the University of Auckland, led the largest study of gastric cancer done in New Zealand.

In his soon-to-be-published paper, 38% of all reports of gastric cancer reached stage 4, meaning the cancer had spread widely from the stomach by the time they were diagnosed. For Māori, the stage 4 figure was 44%.

For those patients, average survival was under four months.

Māori patients were diagnosed at an average age of 61 and Pasifika patients at 63, both about a decade younger than the New Zealand European average of 73.

“This is a disease that is inequitable,” Schauer says.

“It’s worse in Māori, Pacific and Asians, and is causing a huge amount of both morbidity and mortality in our population.”

And this is where Misipeka was lucky. When the cancer was found, it had not spread beyond his stomach, Misipeka’s wife Nola says.

Yet finding it was only a start. A later complication meant his stomach partly split open, needing emergency surgery. Ultimately, the tumour and about half of his stomach were removed.

“Luckily our doctor was very persistent,” Nola says.

Five months on, Misipeka is eating small portions, slowly regaining strength and easing back into a bit of gardening.

“I was pretty lucky that I went past 80s. A lot of young ones died a lot earlier.”

During her husband’s ordeal, Nola recalls doctors mentioning “a bug” in his stomach and putting him on strong antibiotics.

Misipeka had never heard of H. pylori. “It was a complete surprise,” he says.

Learning of the harm H. pylori can have, the couple are spreading the message, insisting their extended family get tested for the bacteria.

Schauer says the most effective way to decrease stomach cancer rates is finding and eradicating the greatest cause – H. pylori infections – before cancer forms.

“It requires a paradigm shift in thinking where we go from the ambulance at the bottom of the cliff waiting for patients to present with abdominal pain, bleeding, weight loss, inability to swallow, and shifting to a preventive mechanism where we know that we can prevent this from happening and prevent the cascade of inflammation and cancer.”

The need for a screening programme

Whether a doctor finds an H. pylori infection in New Zealand comes down to ticking the right boxes and a bit of luck.

Finding an infection should go like this: a patient turns up to their GP with symptoms like burning or pain in the upper abdomen, bloating, nausea or general stomach discomfort after meals – conditions labelled dyspepsia – and that’s a tick in the check for H. pylori box.

If the patient lives in northern New Zealand, is Māori, Pasifika or Asian, was born overseas where infection rates are high, has a family history of stomach cancer or lives in a crowded home, that’s tick, tick and tick.

A combination of those check marks means a doctor should request a test, usually a stool sample sent to a lab.

If you have H. pylori but no symptoms, or don’t fit the risk profile, then nobody’s ticking boxes.

Dr Andrea Teng, of the University of Otago, Wellington, co-leads New Zealand's first population-wide study of H. pylori infection.

And even patients who do have both symptoms and the risk factors get missed, says Dr Andrea Teng, a public health researcher at the University of Otago.

“Māori and Pacific, we know, have the highest rates of infection and are actually less likely to get tested than European and Asian groups.

”The current approach is not reaching the groups that need it the most.”

Teng and a team of researchers have finished New Zealand’s first population-wide survey of H. pylori infection, testing 1107 people aged 12 to 69.

The results are preliminary but the pattern is clear.

Blood tests, which show whether someone has ever been infected, found 48% of Pasifika participants and 15% of Māori participants had been, compared with 9% of European New Zealanders.

Around 3% of people who carry H. pylori go on to develop stomach cancer, Teng says.

Trials that followed people for about 10 years found treating those who tested positive cut stomach cancer by almost half.

A real programme won’t match a trial, because not everyone takes up an invitation or follows through.

“We know that it’s effective from the trials, so it’s just implementation questions,” she says.

A working group hosted by the International Agency for Research on Cancer, part of the World Health Organisation, and including Teng, concluded that screen-and-treat programmes are cost-effective, and may even save money, in high-risk populations.

Modelling based on 2011 data and prices found screening and treating for H. pylori would be good value.

Aimed at Māori, it would cost about $12,000 for every extra year of healthy life gained.

Offered to every adult aged 25 to 69, it would cost about $24,600.

At the time of the modelling, the benchmark for good value was $45,000.

“It’s just really good value for money,” Teng says.

“That’s where I think New Zealand needs to be – piloting an H. pylori screening programme.”

And Schauer agrees.

“We have overwhelming evidence that this is an excellent thing to do, but it really has to be stratified based on risk,” he says.

“I think we should really consider seriously a screen and treat programme for high-risk populations in New Zealand.”

And the Ministry of Health has long agreed, making such a programme one of three priorities in the 2020 Cancer Action Plan.

So what is the hold-up?

Dr Karen Bartholomew, Health NZ’s director of health gain development, says a national programme has to be carefully considered, including research, the cost, impact on populations and whether any system is ready.

Yet, the National Screening Advisory Committee, which Bartholomew chairs and advises on whether new national programmes go ahead, “has not yet reviewed H. pylori screening for gastric cancer”.

“It is on the list for future consideration,” Bartholomew says.

Health NZ is running feasibility studies on adding H. pylori testing to bowel screening, she says.

The Cancer Action Plan was updated in 2026 and has set one dated H. pylori goal – make a plan to design a pilot scheme by 2027.

New Zealand’s delay isn’t unusual.

The international agency Teng contributed to has recommended countries consider screening high-risk groups since 2014, and a report in the New England Journal of Medicine this year found implementation has met with “hesitation and limited action”.

It counts just three population-level programmes worldwide.

Schauer believes New Zealand should mirror others.

“In New Zealand, we like to have ingenuity but I think what we should do in this instance is see if we can just copy and translocate what’s worked very well in other countries.”

Killing H. pylori – it’s getting tricky

Nobel laureate Barry Marshall, who drank a broth of H. pylori in 1984 to prove it causes stomach disease. Photo / Chen Wen, China News Service via Getty Images

It took a “crazy” scientist to prove the link between H. pylori and stomach diseases.

Doctors used to believe nothing could survive the stomach’s acid. Gastritis and ulcers were blamed on stress, spicy food, too much acid.

Research by Australian physicians Robin Warren and Barry Marshall started linking the conditions to bacteria discovered living in the stomach.

In 1984, after experts dismissed the research and animal testing failed, Marshall decided to become the petri dish and drank a broth swimming in H. pylori.

Within days, he was vomiting, with gastritis spreading through a stomach that had been clear a week before.

In 2005, Marshall and Warren won the Nobel Prize in Medicine for their work.

“People thought he [Marshall] was a bit crazy,” says Dr Tom Mules, a gastroenterologist at the Malaghan Institute.

Nearly everyone who carries H. pylori caught it by their 10th birthday.

“This is acquired typically in childhood, and typically from your family members you’re living with,” Mules says.

There are two main strains of the bacterium – a Western strain and a more aggressively cancer-driving East Asian strain, he says.

Because it’s passed down within families, a strain tends to stay within the same ethnic communities for generations. Māori and Pasifika populations are thought more often to carry the East Asian version, a possible factor behind New Zealand’s higher gastric cancer rates among those groups.

The standard Kiwi treatment to eliminate H. pylori is called triple therapy – taking two broad-spectrum antibiotics and an acid-suppressing drug for two weeks. The treatment works for most, with an 85% or greater chance of clearing infection.

Dr Tom Mules, a gastroenterologist and researcher at the Malaghan Institute, is working on an mRNA vaccine for H. pylori. Photo / Supplied

However, H. pylori is growing antibiotic resistance.

“If we look at Clarithromycin, which is the main antibiotic that New Zealand uses to treat Helicobacter pylori, our resistance rates are probably sitting around maybe the 10% mark,” Mules says.

“If you go to some countries in the world, particularly Europe, like France, it’s sitting more around 40% and so they’ve abandoned that therapy completely.”

Mules, an expert in H. pylori’s biology, is racing to offset growing antibiotic resistance.

At the Malaghan Institute, they have developed a molecular test that can detect resistance genes straight from a patient’s stool sample, meaning doctors could prescribe the right antibiotic the first time, rather than guessing, he says.

Mules is also chasing the “holy grail” – a vaccine.

“Because we know what causes the stomach cancer, why can’t we prevent that cause?” he says.

“Kind of in the same way that we do with cervical cancer and HPV.”

Development won’t be simple – 30 years of attempts by researchers worldwide have failed to deliver – so far.

A vaccine, if it comes, would protect the next generation. For the people carrying H. pylori now, the answer is to find it and treat it.

Misipeka’s advice is simple.

“Just go to the doctor and get all checked out,” he says.

“If you leave it too long ... it will get worse and it’s harder to fix.”

Mike Scott is a senior journalist at the Herald. His work spans writing, photography and video and he has won numerous journalism awards, including Videographer of the Year and Best Documentary. He has worked in media for more than 25 years, producing stories across New Zealand and internationally.