Endogenous and exogenous infection with Pseudomonas aeruginosa in a burns unit

Twenty patients who were admitted to the Burns Unit from December, 1969 through October, 1970 were studies to determine the sources of infection caused by Pseudomonas aeruginosa. The pyocine typing method was employed for finger printing of 383 isolates recovered from wounds and 67 isolates from environmental cultures of nurses' hands, sinks, floors, bed rails, walls and baths. In addition, cultures of moist rectal swabs were carried out daily for the first six days of hospitalization to assess the importance of endogenous infection. In six patients, the rectum was identified as the source of infection. However, in these patients, pyocine types of Ps. aeruginosa which were not obtained from rectal cultures, were also recovered. Pyocine types 1b, 10 and 31 were isolated more frequently than others. Clustering of common pyocine types suggests cross-contamination. Sinks were found to be consistently contaminated with Ps. aeruginosa. Amongst the environmental sources, positive cultures were occasionally obtained from floors, bed rails and nurses' hands. It is suggested that sinks are probably the most important reservoir of Pseudomonas infection in burns.