An ultrastructural demonstration of the agent of Legionnaires' disease in the human lung.

The authors have provided ultrastructural demonstration from human material of a small rod shaped organism that represents the causative agent of Legionnaires' disease. The organisms are found mainly in intracytoplasmic vacuoles of alveolar cells. They have a thin outer cell wall and a more delicate plasma membrane. On the basis of morphology, arguments are presented to classify these unusual organisms as rickettsia-like.