Legionnaires' disease (LEE-juh-nares) is caused by a type of bacterium calledLegionella (LEE-juh-nell-a). The bacterium is named after a 1976 outbreak, when many people who went to a Philadelphia convention of the American Legion suffered from this disease, a type of pneumonia (lung infection). A milder infection, also caused by Legionella bacteria, is called Pontiac fever. The term "legionellosis" (LEE-juh-nuh-low-sis) may be used to refer to either Legionnaires' disease or Pontiac fever.
The pictured magazine covers feature the work of public health professionals in 1976 as they raced to trace the origin of the first documented outbreak of Legionnaires' disease in Philadelphia, Pennsylvania.