Independent risk factors associated with hospital-acquired pneumonia in an adult ICU: 4-year prospective cohort study in a university reference hospital

Hospital-acquired pneumonia (HP) is the most common infection in adult intensive care units (ICUs). To develop effective strategies to prevent it, we identified factors that independently increased the risk of contracting HP while admitted at an ICU. We performed a prospective cohort study during 4 years in which we included all patients who had been admitted for at least 24 h to the ICU at a university reference hospital in Spain. We conducted a multivariable Cox regression analysis to obtain adjusted hazard ratios (HR). The dependent variable for patients with HP was duration of ICU stay prior to the onset of HP. For those without HP, the dependent variable was duration of stay between admission and discharge from the ICU. The independent variables were intrinsic characteristics of the patients already present at admission to the ICU and diagnostic or therapeutic procedures performed during admission. We studied 4427 patients, of which 233 (5.3%) developed HP while admitted to the ICU. The strongest independent risk factors associated with the occurrence of HP were mechanical ventilation (HR = 8.2; 95% CI = 3.6-18.9) and the use of a nasogastric tube (HR = 2.3; 95% CI = 1.6-3.3). The intrinsic risk factors that were part of the model were the presence of decreased level of consciousness upon admission (HR = 2.0; 95% CI = 1.5-2.7) and the APACHE II index (HR = 1.018; 95% CI = 1.002-1.035). Although severity of illness upon admission (APACHE II index) and decreased level of consciousness were relevant predisposing factors to contract HP in the ICU, the strongest association corresponded to extrinsic factors such as mechanical ventilation and use of a nasogastric tube. The fact that these are therapeutic interventions facilitates developing prevention and control measures that can contribute to reduce the risk for HP.