Pseudomonas aeruginosa outbreak in a burn unit: role of antimicrobials in the emergence of multiply resistant strains.

An environmental survey and a cohort study were done to analyze an outbreak of infections in a burn unit caused by a serotype O:11 and a multidrug-resistant serotype O:12 Pseudomonas aeruginosa. The P. aeruginosa O:11 outbreak was controlled by eradicating an environmental source, contaminated hydrotherapy equipment. To assess risk factors for infections caused by P. aeruginosa O:12, 15 infected burn patients were compared with 32 noninfected burn patients hospitalized during the outbreak. Patients had similar extent, severity, location, and care of burn injuries, exposure to invasive procedures, and past history of P. aeruginosa infection. Prior treatment with ceftazidime (3 g/day) was the only independent risk factor for P. aeruginosa O:12 infection. The outbreak was controlled by increasing the daily administration of ceftazidime from 3 to 6 g and by a reinforcement of isolation precautions.