Sohn KM, et al. Ciprofloxacin-resistant P. mirabilis bacteremia 91 Table 2. Factors associated with ciprofloxacin resistance in Proteus mirabilis isolates causing bacteremia Ciprofloxacin-resistant (n = 10) Ciprofloxacin-susceptible (n = 27) 6 (60.0) 9 (33.3) 5 (50.0) 5 (18.5) 1 (10.0) 7 (70.0) 0 (0) 2 (20.0) 5 (50.0) 3 (30.0) 2/8 (25.0) 2 (20.0) 3/8 (37.5) 3/8 (37.5) 2/8 (25.0) 3/8 (37.5) 6 (60.0) 10 (37.0) 7 (25.9) 3 (11.1) 4 (14.8) 0 (0) 3 (11.1) 1/18 (5.6) 1 (3.7) 0/18 (0) 0/18 (0) 0/18 (0) 1/18 (5.6) 3 (11.1) Male gender Nosocomial infection Underlying diseases Solid tumor Neurologic disease Renal disease Diabetes mellitus Comorbid conditions Recent operation Corticosteroid use Central venous catheterization Indwelling urinary catheter L-tube Percutaneous tube Prior invasive procedure Prior use of antibiotics ESBL production Values are presented as number (%). ESBL, extended-spectrum β-lactamase. determined to have community-onset infections, five (19%) had ciprofloxacin-resistant bacteremia. Among the ten patients identified as having a nosocomial-acquired infection, five (50%) had ciprofloxacin-resistant bac- teremia (p = 0.094). Risk factors associated with ciprofloxacin-resistant P. mirabilis are listed in Table 2. Univariate analysis revealed a significant relationship between ciprofloxacin- resistant P. mirabilis bacteremia and neurologic disease, recent operation, L-tube insertion, percutaneous tube use, and ESBL production (all p < 0.05). ESBL was detected in six (60%) of ten ciprofloxacin-resistant P. mirabilis iso- lates. In comparison, only three (11%) of 27 ciprofloxacin- susceptible P. mirabilis isolates were ESBL producers. ESBL production was significantly associated with ciprofloxacin resistance among P. mirabilis isolates caus- ing bacteremia (OR, 12.00; 95% CI, 2.10 to 68.6; p = 0.005). In a logistic regression analysis, ESBL production remained a significant factor associated with ciprofloxacin resistance, after adjusting for nosocomial infection, neuro- logic disease, or recent operation (OR, 13.93; 95% CI, 1.04 to 186.07; p = 0.046). Four (40%) of ten patients with ciprofloxacin-resistant bacteremia received inappropriate initial antimicrobial therapy, while three (11%) of 27 patients with ciprofloxacin-susceptible bacteremia received inappropri- ate initial antimicrobial therapy (p = 0.069). Of 32 p value 0.258 0.094 0.224 0.023 0.548 0.653 0.001 0.166 0.215 0.172 0.022 0.022 0.086 0.072 0.005 patients whose outcomes could be evaluated, eight (25%) died within 30 days; no significant difference was found between ciprofloxacin-resistant (1/9, 11%) and -suscepti- ble (7/23, 30%) patients (p = 0.386). When factors associ- ated with mortality were evaluated, solid tumor was found to be the only significant factor associated with mortality (p = 0.005). DISCUSSION This study revealed that neurologic disease, recent oper- ation, L-tube insertion, and percutaneous tube were sig- nificant risk factors associated with the development of bacteremia caused by ciprofloxacin-resistant P. mirabilis. Ciprofloxacin resistance in K. pneumoniae has been reported to be closely associated with ESBL production [9]. Several studies have examined the relationship between quinolone resistance and ESBL production in E. coli and K. pneumoniae [10,11]. Ciprofloxacin-resistant Enterobacter bacteremia is closely associated with broad- spectrum cephalosporin resistance [12]. Consistent with the latter study, we also observed a close association of ciprofloxacin-resistant P. mirabilis bacteremia with broad-spectrum cephalosporin resistance conferred by ESBL. This association is of great concern because ESBL-pro-