Ciprofloxacin resistance among nosocomial Pseudomonas aeruginosa and Staphylococcus aureus in the United States.

We attempted to determine if an increase in resistance to ciprofloxacin occurred among nosocomial pathogens, especially Pseudomonas aeruginosa and Staphylococcus aureus. 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. 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. 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.