Origin and spread of Pseudomonas aeruginosa, Proteus and Klebsiella during twenty years in an infectious hospital.

Bacteriological examinations carried out in an infectious hospital revealed that the occurrence of Pseudomonas and Proteus grew 4-fold, and the rate of Klebsiella positive cultures 3.5-fold between 1958 and 1977. On the other hand, the occurrence of Staphylococcus aureus decreased to the half since 1961. The occurrence of Gram-negative facultative pathogens started to increase in the surgical wards in the fifties and the rise lasted until the mid-sixties. Pseudomonas aeruginosa was the most frequent among them. In contrast, Escherichia coli dominated and P. aeruginosa was the least frequent in the non-surgical wards. Here the Gram-negative facultative pathogens showed a more rapid increase and the incidence of P. aeruginosa and Proteus kept rising throughout the whole examination period. When Gram-negative facultative pathogens of hospital origin were colonizing, the proportion of sick persons versus symptomless carriers was significantly higher than in the case of extrahospital colonization on the basis of the records of 300 P. aeruginosa, 300 Proteus and 300 Klebsiella positive patients. This proportion changed parallel with the rate of the strains of hospital origin. The number of patients who acquired P. aeruginosa, Proteus or Klebsiella extrahospitally, kept continuously rising between 1958 and 1971. Thus, the advance of Gram-negative facultative pathogens is due not ony to nosocomial causes.