[Peptic ulcer disease and helicobacter pylori: How we know what we know]

The bacterium Helicobacter pylori is one of the main causes of peptic ulcers. But how was this causal relationship demonstrated? A historical and philosophical analysis of a series of studies conducted during the 1980s can elucidate the question. In the beginning, a mere correlation between the newly discovered bacterium and peptic ulcers was found in gastric biopsies. It remained an open question whether the bacterium caused the disease, or whether it constituted merely an opportunistic infection. Yet determining the direction of causality was difficult in the absence of an animal model: Even though gastritis was observed in a courageous self-experiment involving a swallowed bacterial culture, tf!e significance of the individual case was small. The failings of the self-experiment could only be rectified by a randomised, placebo-controlled trial which met the requirements of Koch's third postulate. Moreover, it was necessary to gain an initial understanding of the mechanism by which the causal relationship between H. pylori and peptic ulcers is mediated: How, forexample, does the bacterium survive in the acid environment of the stomach? The study of the case from the perspective of the history and philosophy of science illustrates how medical knowledge is established incrementally.