One bacterium causes roughly 1 in 20 cancer cases worldwide. It’s the most cancer-causing pathogen we’ve found—and the main cause of peptic ulcers. Its discovery overturned an ironclad medical dogma that the stomach was sterile.

Despite infecting about half of humanity, Helicobacter pylori wasn't discovered until 1979 and shown to cause gastritis and peptic ulcer disease in the early 1980s. Why did it evade detection for so long—and what finally broke through the consensus?

I went to Perth, Australia—where H. pylori was first discovered—to chat with Barry Marshall, gastroenterologist and co-recipient (with Robin Warren) of the 2005 Nobel Prize in Physiology or Medicine for discovering H. pylori and proving that it causes gastritis and peptic ulcer disease. Marshall famously infected himself with the bacterium to demonstrate causality and later helped develop clinical diagnostics like the urea breath test, which we demo live in the episode.

We discuss:

the rise and fall of stomach cancer in the West;
whether Darwin’s dyspepsia and Napoleon's stomach cancer trace to H. pylori;
the ulcer–cancer paradox;
Correa’s cascade: what H. pylori eradication reverses—and what it doesn’t;
the “H. pylori enigmas” (Africa, India, Costa Rica);
eradication prospects and an oral vaccine timeline;
how the field missed the discovery;
how the primitive internet enabled the discovery;
what the H. pylori discovery teaches us about how knowledge diffuses;
lessons from manufacturing millions of tests in Perth;
and much, much more.

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The Facts of Life by Pádraig Ó Tuama