A nosocomial outbreak of infections due to multiply resistant Proteus mirabilis: role of intestinal colonization as a major reservoir.

An outbreak of nosocomial infections involving an unusual strain of multiply resistant Proteus mirabilis (phage type 8888) occurred in 15 patients, 14 of whom were in the surgical intensive care unit at that time. No common source of infection was identified, and person-to-person transmission was the most likely mode of spread. Case-control analysis indicated a significantly increased risk infection related to length of hospital stay (P less than 0.005), number of operations (P less than 0.005), proximity to another case (P less than 0.01), number of antibiotics received (P less than 0.02), and use of a respirator (P less than 0.01). Only the number of operations (P less than 0.01) and proximity to another case (P less than 0.05) remained significant risk factors when related parameters were controlled by multivariate analysis. Thirteen of 14 patients prospectively cultured were colonized by the epidemic organism in the intestinal tract, while rectal carriage preceded infection by the same strain in at least four patients. These data suggest that intestinal colonization may have been an important reservoir for this outbreak, and the findings may explain the unduly prolonged course of intrahospital spread as well as the difficulty encountered in the eradication and control of the outbreak.