Legionnaires’ disease is an infection that most commonly occurs as pneumonia, with symptoms of fever, cough, chest pain, and difficulty breathing. Legionnaires’ disease usually afflicts people who already have another illness–such as lung disease–and those who have received organ transplants.
Legionnaires’ disease was first identified in July 1976, when an epidemic of pneumonia struck 221 people attending an American Legion convention in a Philadelphia hotel. Thirty-four of those stricken with the disease died. Physicians did not know what caused the illness, which they named Legionnaires’ disease.
In 1977, scientists discovered the cause of the pneumonia, a bacterium later named Legionella pneumophila. This bacterium is unusual because it can invade white blood cells and multiply within them. White blood cells normally defend against infections. The bacterium commonly occurs in water supplies. Many outbreaks of Legionnaires’ disease have been linked to the presence of the bacteria in drinking water. People get the disease by inhaling water droplets or by aspirating (drawing into the lungs) water containing the bacterium.
Physicians diagnose Legionnaires’ disease by testing for antibodies to the bacterium in the blood or by detecting the bacterium in the mucus coughed up from the lungs. The disease can be treated with such antibiotics as erythromycin and rifampin. Legionnaires’ disease bacteria in water supplies may be killed by heating the water to high temperatures, by treating it with chlorine or ions from an alloy of copper and silver, or by exposing it to ultraviolet light.
