In March 1919, shortly after the end of World War I, some American war veterans met in Paris to create an organization to help demobilized combatants and their families.

A month later, in St. Louis, promoters and new adherents founded The American Legion, based in Indianapolis, thus seeking to maintain nonpartisanism, very difficult to sustain in Washington.

From now on, the American Legion has grown in membership – some three million members – it has collaborated with the US government in different war efforts (World War II, Korean, Vietnam, Gulf, Iraq, Afghanistan, etc.), has lobbied on behalf of veterans, their relatives and their descendants, has raised funds for medical and educational aid and has been a refuge for thousands of ex-soldiers in times of difficulty, but always keeping a low profile and very little known outside the United States, until the 1976 annual convention held in a Philadelphia hotel. About 200 members of the Legion, many of them older men, staying at the hotel, suddenly presented a picture of fever, prostration, non-productive cough, shortness of breath, confusion and rapid deterioration of the general condition, with a very high mortality, of about 20%.

Chest radiographs showed typical densities of severe bacterial pneumonia but no specific features. What germ was producing that explosive epidemic of pneumonia in men who until a few hours before were in good health? Serological tests, sputum tests and radiographs did not give strong clues. Treatment, with intravenous antibiotics and intensive support measures, helped some and was useless in others. At the CDC in Atlanta all the alarms sounded and a race against time began immediately.

Shortly after, the enemy was identified. It was a strain, unknown until then as a pathogen, of an aerobic gram negative bacillus that does not grow in the usual culture media, but in a specific one called BCYE (buffered charcoal yeast extract). It was called, it could not be less, legionella, and it was discovered that its natural habitat is the deposited water (air conditioning trays in this case) and its transmission medium, the microdroplets of this water vaporized by the air current. The investigations of the CDC scientists defined the neighborhood of the rooms of those affected and the links between them by the air ducts.

Since then and forever, the American Legion has, to the dismay of many of its members, a bacterium and a disease (legionellosis) that bears his name. This is how the American Legion became known throughout the world.