Legionnaires' disease: ultrastructural appearance of the agent in a lung biopsy specimen.

During the Legionnaires' disease epidemic that occurred in Philadelphia in 1976, we performed a transbronchial lung biopsy on a patient who suffered from Legionnaires' disease that was confirmed by serology. The biopsy was performed in an attempt to detect a causal agent for the patient's pneumonia at a time when the cause of the epidemic was a mystery. We detected pleomorphic microbial structures that were both intracellular and extracellular in location. By electron microscopy, they ranged in size from 350 nm to 2.5 mu. Some displayed cell walls and fine cytoplasmic granules that resembled ribosomes. Our findings illustrate the appearance of the Legionnaires' disease agent in acutely infected, antibiotic-treated human lung obtained from biopsy specimens.