A nosocomial outbreak of fluoroquinolone-resistant salmonella infection.

Background: Infection with fluoroquinolone-resistant strains of salmonella is rare, as is nosocomial salmonella infection. We describe the first recognized outbreak of fluoroquinolone-resistant salmonella infection in the United States, which occurred in two nursing homes and one hospital in Oregon. Methods: We interviewed medical staff and reviewed patients' charts and death certificates. In Nursing Home A we conducted a case-control study. Patients were defined as residents of the nursing home from whom fluoroquinolone-resistant Salmonella enterica serotype Schwarzengrund was isolated between February 1996 and December 1998. Controls were residents with similar medical conditions whose cultures did not yield salmonella. Results: Eleven patients with fluoroquinolone-resistant salmonellosis were identified at two nursing homes. In nine patients a urine culture was positive, in one a stool culture, and in one a wound culture. The index patient had been hospitalized in the Philippines and had probably acquired the infection there. Transmission was probably direct (from patient to patient) or through contact with contaminated surfaces. Treatment with fluoroquinolones during the six months before a culture was obtained was associated with a significant risk of salmonella infection. More fluoroquinolones were used at Nursing Home A than at similar nursing homes in Oregon. The isolates from the outbreak had similar patterns on pulsed-field gel electrophoresis and the same gyrA mutations. The isolates from the outbreak were also similar to the only previous isolate of fluoroquinolone-resistant salmonella in the United States, which came from a patient in New York who had been transferred from a hospital in the Philippines. Conclusions: We describe a prolonged nosocomial outbreak of infection with fluoroquinolone-resistant S. enterica serotype Schwarzengrund. More such outbreaks are likely in institutional settings, particularly those in which there is heavy use of antimicrobial agents. (N Engl J Med 2001;344:1572-9.) Copyright (C) 2001 Massachusetts Medical Society.