Previous antibiotic exposure and evolution of antibiotic resistance in mechanically ventilated patients with nosocomial infections.

Purpose: This study aimed to evaluate the impact of previous antibiotic exposure and the influence of time interval since exposure on the evolution of antibiotic-resistant infections.

Methods: We retrospectively analyzed 167 mechanically ventilated patients with nosocomial infections over a 3-year period, with focus on infections in the bloodstream, urinary tract, lower respiratory tract, and surgical sites.

Results: Of 167 patients, 62% were confirmed as antibiotic resistant. The most common isolated pathogen was extended-spectrum β-lactamase Enterobacteriaceae (43.9%), followed by methicillin-resistant Staphylococcus aureus (22.8%), and carbapenem-resistant Acinetobacter baumannii (17.5%). Multivariate analysis revealed that the association between resistance and the time interval increased within 10 days (odds ratio [OR], 2.45; P=.133) and peaked at 11 to 20 days (OR, 7.17; P=.012). The data were categorized into 2 groups: when the time interval was more than 20 days, there was a 23.9% reduction in resistance rate compared with when the time interval was 20 days or less (OR, 0.36; P=.002).

Conclusions: Although antibiotic exposure increased resistance rate in nosocomial infections, this association decreased as time interval increased. Antibiotic stewardship should consider the significance of time interval while investigating the evolution of subsequent antibiotic-resistant infections.