Clinical isolation and resistance patterns of and superinfection with 10 nosocomial pathogens after treatment with ceftriaxone versus ampicillin-sulbactam

Isolation of pathogens from clinical cultures and their resistance patterns may be altered by antecedent antibiotic treatment. The objective of this s tudy was to assess the influence of treatment with ceftriaxone versus that with ampicillin-sulbactam on recovery and superinfections with 10 nosocomia l pathogens. The study mas designed as a historical cohort study, using a p ropensity score to adjust for confounding by indication and multivariate su rvival analyses to adjust for other confounding. Two thousand four hundred forty-five patients were treated with ampicillin-sulbactam, and 1,308 were treated with ceftriaxone. The study analyzed two outcomes: (i) recovery of pathogens from clinical cultures and (ii) microbiologically documented infe ctions. Data were obtained from administrative, pharmacy, clinical, and lab oratory databases and by chart extraction. Following treatment, new isolati on of at least 1 of the 10 target pathogens occurred for 244 patients. Afte r adjustment, more infections occurred in the ampicillin-sulbactam group (h azard ratio [HR], 1.55; P = 0.009). This was observed,vith all gram-negativ e rods combined (HR, 3.6; P < 0.001) and with each genus of the family Ente robacteriaceae. No differences in isolation of gram-positive bacteria mere evident (P = 0.33). Microbiologically documented superinfections occurred i n 172 patients and were less frequent in the ceftriaxone group (3.8% versus 5%; HR, 1.6; P = 0.015). All the Escherichia coli and Klebsiella spp. isol ates were susceptible to ceftriaxone, but half were resistant to ampicillin -sulbactam. The prevalence of oxacillin resistance among Staphylococcus aur eus isolates was higher in the ceftriaxone group (63% versus 31%; odds rati o, 3.8; P = 0.08). Differences in the rates of superinfections and the like ly causative organisms following treatment with ceftriaxone or ampicillin-s ulbactam were evident. This may guide clinicians in empirical choices of an tibiotics to treat superinfection.