The aim of this study was to elucidate the impact of ICU-acquired infection on ICU and hospital mortality. The main determinants of hospital infection onset were investigated and the role of the most used antibiotics in the ICU was considered a risk factor for selection of peculiar bacterial species responsible for ICU pneumonia.

Patients with a longer than 48 hour stay in a teaching hospital ICU were retrospectively enrolled between January 2005 and December 2006. Risk factors for ICU and hospital mortality were analyzed with a logistic regression model adjusted for age, SAPS II, medical or surgical status of the patients. Univariate analysis permitted one to verify the relation between previous exposition to an antibiotic therapy and development of ICU pneumonia.

Of 343 patients enrolled, 39 had a diagnosis for ICU infection: 18 had an infection on admission developing a second infection during ICU stay, and 21 had a primary infection after ICU admission. Among the patients with ICU-acquired infection, ICU mortality and hospital mortality were more than doubled (OR = 2.51 (95% CI = 1.05–5.98) and OR = 2.32 (95% CI = 1.10–4.86), respectively). Having more than one infection demonstrated an ICU mortality risk addiction more than tripled (OR = 3.36 (95% CI = 1.06–10.61)). Admission severity and an infection before ICU admission emerged as important risk factors for ICU-acquired infections (OR = 5.71 (95% CI = 1.19–27.29) and OR = 3.14 (95% CI = 1.42–6.97), respectively). Previous fluoroquinolone use demonstrated a clear role in favouring Pseudomonas aeruginosa pneumonia and linezolid in Acinetobacter baumannii pneumonia (Table 1).

ICU-acquired infections are an independent risk factor for ICU and hospital mortality. Finally some antibiotic categories might show up as pneumonia inductors but further studies are needed to confirm our hypothesis.