[Effect of previous antibiotic therapy on the epidemiology of ventilator-associated pneumonia]

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in intensive care patients. The aim of the study was to evaluate the effect of previous antibiotic therapy on the incidence of VAP, mortality and spectrum of bacterial pathogens.

The retrospective, observational study comprised patients over 18 years of age meeting the clinical criteria of VAP. Controls were patients requiring mechanical ventilation for more than 48 hours with no signs of VAP. Each group was divided into two arms according to previous antibiotic therapy. Tracheal aspirates and oropharyngeal swabs were taken from all patients. Cultured isolates were identified using standard microbiological techniques. Antimicrobial susceptibility testing was performed according to the European Committee on Antimicrobial Susceptibility Testing guidelines. In both groups, 28-day mortality, 90-day mortality and multidrug-resistant (MDR) bacterial pathogen frequency were evaluated.

The study included 49 patients (32 patients with previous antibiotic therapy, 17 antimicrobial-naive patients). The proportion of individuals with previous antibiotic therapy was significantly lower in VAP patients (34%) than among controls group (66%; p = 0.02). The VAP criteria were met by 23 patients (11 with previous antibiotic therapy, 12 without the therapy). The Enterobacteriaceae including extended-spectrum beta-lactamase-producing strains and Pseudomonas aeruginosa were the most common pathogens isolated. MDR pathogens were statistically significantly more frequent in patients with previous antibiotic therapy (77% vs. 33%; p = 0.047). In patients with previous antibiotic therapy, 28-day mortality was lower (18%; n = 2) than in antimicrobial-naïve patients (33%, n = 4; p = 0.640). The difference was more pronounced in 90-day mortality, albeit with low statistical significance (18%, n = 2 vs. 58%, n = 7; p = 0.089).

Previous antibiotic therapy was associated with a lower incidence of VAP and a higher frequency of MDR bacterial pathogens. VAP antibiotic therapy modified according to knowledge of previous antibiotic therapy and cultured isolates was correlated with lower 28-day and 90-day mortality rates.