Table 1.

Clinical and microbiological characteristics, exposures, and Cox proportional HRs for the emergence of resistance to any of the four study drugs

Characteristic (n = 271)ValueHR (95% CI)aP value
Demographics
 Age (yr); mean (SD)62 (15.6)1.0 (0.98–1.03)0.7
 Male gender; no. (%)162 (59)1.1 (0.5–2.5)0.7
Underlying conditions
 AIDS; no. (%)16 (6)0.9 (0.1–6.7)0.9
 Cancer; no. (%)42 (15)1.2 (0.4–3.0)0.8
 Diabetes; no. (%)145 (53)0.8 (0.4–1.8)0.7
 Solid-organ transplant; no. (%)29 (11)1.2 (0.4–3.1)0.7
 Chronic lung disease; no. (%)38 (14)0.7 (0.2–2.3)0.6
 Charlson score; mean (SD)3.4 (1.8)1.0 (0.8–1.3)1.0
Exposures during admission
 Transfer from institution; no. (%)52 (19)1.5 (0.7–3.4)0.3
 ICU stay; no. (%)76 (28)0.6 (0.3–1.4)0.22
 Surgical procedure; no. (%)127 (46)0.8 (0.4–1.8)0.6
 Nursing indexb; mean (SD)58.4 (25.7)1.0 (0.99–1.01)0.9
 Culturing score; no. (%)97 (35)2.6 (1.1–5.7)0.027
 Rx with study agentd; no. (%)
  Ceftazidime125 (46)0.6 (0.3–1.4)0.25
  Ciprofloxacin98 (36)0.9 (0.4–2.1)0.9
  Imipenem37 (14)2.9 (1.3–6.4)0.008
  Piperacillin91 (33)1.4 (0.6–3.1)0.4
 Rx with >1 study agentd; no. (%)66 (24)1.4 (0.6–3.1)0.4
 Rx with aminoglycosides; no. (%)77 (28)1.3 (0.6–2.7)0.6
Baseline isolate
 Hospital days before culture; mean (SD)4.3 (8.0)1.02 (0.99–1.05)0.07
 Nosocomial isolate; no. (%)90 (33)1.2 (0.6–2.7)0.7
 Number of resistancese; mean (SD)0.47 (0.76)1.2 (0.8–2.0)0.4
 Culture site; no. (%)
  Blood14 (5.1)0.5 (0.1–4.0)0.5
  Effusion fluid13 (4.7)2.4 (0.7–8.2)0.15
  Respiratory tract61 (22)0.8 (0.3–1.9)0.6
  Urine40 (15)1.1 (0.3–3.7)0.9
  Wound129 (47)1.1 (0.5–2.4)0.8
  Other16 (5.8)0.8 (0.2–3.7)0.8
  • a CI, confidence interval.

  • b Total nursing hours/number of days inside the hospital.

  • c Number of cultures from the baseline isolate/days of follow-up (dichotomized at mean).

  • d Time-dependent variable (see text); Rx, treatment.

  • e The baseline isolate could be already resistant to zero, one, two, or three of the four study drugs.