The bug that hit on Independence Day
15 Jan 2000
The bicentennial of the signing of the Declaration of Independence in July 1976 was the cue for parties across the US. One, a gathering of members of the American Legion at a Philadelphia hotel, was to have far-reaching consequences for medicine and, later, for the process industries. Some 200 of the attendees fell ill with a severe pneumonia-like fever. The unfortunate victims gave the name to Legionnaire's Disease, and later to the bacterium causes it, Legionella pneumophillia.
L. pneumophillia is one of 40 species of Legionella found in water around the world, and itself exists in 15 different groups. Related to the bacteria which cause tuberculosis and salmonella, it attacks 2-5 per cent of people exposed to it; of these, 5-15 per cent die. Despite its unusual mode of infection - it paralyses immune cells and multiplies inside them - the bacteria can be treated with powerful antibiotics such as erythromycin. However, even this doesn't kill the bacteria; it merely stops them reproducing inside cells, which gives the immune system a chance to overwhelm the infection. If the victim has weakened lungs - for example, if they are elderly, smokers or heavy drinkers, or have damaged immune system - it can still be fatal. Oddly, men are more than twice as susceptible as women.
Presence of legionella alone is not enough to pose a risk; in fact, the bug is virtually ubiquitous in water supplies. The risks arise when the water is warm, either naturally or through artificial heating, and allowed to form an aerosol or vapour. Legionella is not harmful if drunk, and only causes disease if it can be breathed into the lungs.
