Ciprofloxacin Resistance among Nosocomial Pseudomonas aeruginosa and Staphylococcus aureus in the United States

Abstract
Objective: We attempted to determine if an increase in resistance to ciprofloxacin occurred among nosocomial pathogens, especially Pseudomonas aeruginosa and Staphylococcus aureus. Methods: We examined 1989-1992 ciprofloxacin susceptibility results from 8,517 P aeruginosa and 9,021 S aureus isolates associated with nosocomial infections reported to the National Nosocomial Infections Surveillance System. Results: For S aureus, 27.1% of isolates were resistant to ciprofloxacin; of methicillin-resistant S aureus isolates, 80% also were resistant to ciprofloxacin. A logistic regression model found that ciprofloxacin resistance was more common among S aureus isolated from the urinary and respiratory tracts than from other sites of isolation, and among isolates that were methicillin resistant. After controlling for these factors, the model showed a 123% increase in the odds of ciprofloxacin resistance from 1989-1990 to 1991-1992. For P aeruginosa, 4.7% of the isolates were resistant to ciprofloxacin. Resistance varied by site of infection and rose most dramatically for respiratory tract isolates from 2.0% in 1989-1990 to 5.3% in 1991-1992. Conclusion: Resistance to ciprofloxacin is more frequent among nosocomial S aureus than among P aeruginosa and is increasing rapidly among S aureus isolates and from selected sites among P aeruginosa isolates.

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