Though a contaminated air-conditioning unit was the source of the famous 1976 outbreak, researchers have since discovered that is not the only way the disease can spread. Legionella can contaminate the hot-water side of tap water systems in homes and offices. In addition, dust from construction sites sometimes spreads the bacteria. However, the disease does not seem to spread directly from one person to another. Legionnaires' disease is a form of pneumonia that may also attack other parts of the chest cavity.
Infection sometimes can spread into the abdominal region.
Before the advent of air conditioning and humidifiers, Legionnaires' disease was undetected. There may have been occasional instances, but the first known large-scale outbreak occurred in 1976. Incidence Like the bacterium itself, Legionnaires' disease can be found in most parts of the world. Though it can strike at any time of the year, the disease is most common from June through October. Many cases have been diagnosed in the United Kingdom and other European countries.