Scientific triumphalism and learning from facts: bacteriology and the "Spanish flu" challenge of 1918.

The devastating influenza pandemic known as 'Spanish flu', which killed at least 20 million people all over the world in 1918, was responsible for the first bitter blow inflicted on triumphant bacteriology, fortified by the series of resounding successes achieved in identifying the pathogenic agents of terrible diseases such as anthrax, cholera, tuberculosis, plague, and syphilis. Over-confidence and the idea, born of the Pasteur revolution, that every infectious disease was caused by a bacterium, had led the scientific community to accept the theory put forward by the German bacteriologist, Richard Pfeiffer, who, in 1892, believed he had identified the pathogenic influenza agent in a bacterium, Haemophilus influenzae. But, while the most appalling epidemic ever to sweep through the world since the 'Black Death' of the 1300s was still raging, the scientific community had to admit that influenza originated not from a microbe, but from a virus. This article aims to reconstruct the enlightening and little-known cultured/scientific events and issues of the dramatic crisis that bacteriology experienced in the autumn of 1918, with the consequent simultaneous collapse of both the 'Pfeiffer doctrine' on the microbial origin of influenza and the illusion of a world free of infectious diseases. This was an illusion destined to surface again at the end of the century and collapse with the advent of AIDS.