An explosive, common-source outbreak of pneumonia caused by a previously unrecognized bacterium affected primarily persons attending an American Legion convention in Philadelphia in July, 1976. Twenty-nine of 182 cases were fatal. Spread of the bacterium appeared to be air borne. The source of the bacterium was not found, but epidemiologic analysis suggested that exposure may have occurred in the lobby of the headquarters hotel or in the area immediately surrounding the hotel. Person-to-person spread seemed not to have occurred. Many hotel employees appeared to be immune, suggesting that the agent may have been present in the vicinity, perhaps intermittently, for two or more years.

To identify the etiologic agent of Legionnaire's disease, we examined patients' serum and tissue specimens in a search for toxins, bacteria, fungi, chlamydiae, rickettsiae and viruses. From the lungs of four of six patients we isolated a gram-negative, non-acid-fast bacillus in guinea pigs. The bacillus could be transferred to yolk sacs of embryonated eggs. Classification of this organism is incomplete. We used yolk-sac cultures of the bacillus as antigen to survey suspected serum specimens, employing antihuman-globulin fluorescent antibody. When compared to controls, specimens from 101 to 111 patients meeting clinical criteria of Legionnaires' disease showed diagnostic increases in antibody titers. Diagnostic increases were also found in 54 recent sporadic cases of severe pneumonia and, retrospectively, in stored serum from most patients in two other previously unsolved outbreaks of respiratory disease. We conclude that Legionnaires' disease is caused by a gram-negative bacterium that may be responsible for widespread infection.

No abstract

Two outbreaks of postoperative wound infections due to organisms of the Mycobacterium fortuitum complex (Mycobacterium chelonei and M. fortuitum) occurred among patients who underwent open-heart surgery. In one hospital, 19 of 80 patients who underwent cardiac surgery within a 10-week period developed sternal infection with M. chelonei. In the second hospital, four of nine patients who underwent cardiac surgery within a two-week period developed sternal incisional infection with M. fortuitum. Although epidemiologic investigations uncovered factors that were significantly associated with the development of infection, the source of the infections could not be determined. The results of numerous cultures were negative, but because the investigations were conducted at least two months after many of the patients had had surgery, the materials in use at the time of the surgery were not available for culture. These results emphasize that physicians should be aware that rapidly growing mycobacteria may produce postoperative wound infections.