Underlying illness severity and outcome of nosocomial pneumonia: prospective cohort study in intensive care unit

Previous studies have suggested that the final outcome of a patient with nosocomial pneumonia (NP) may depend on the patient's illness severity upon admission to the intensive care unit (ICU).

To investigate the relationship between developing NP during hospitalization in an adult ICU and the risk of death with special focus on illness severity at admission in the unit.

A prospective cohort study was performed among all patients admitted for at least 24h to the ICU of a university reference hospital in Spain from 2006 to 2009. A stratified univariate study was performed according to the patients' illness severity at admission, estimated using the Acute Physiology And Chronic Health Evaluation (APACHE) II index. To determine whether the NP was independently associated with increased mortality in ICU, a multivariate logistic regression analysis was carried out, adjusting for potential confounders.

In all, 4427 patients were studied, of whom 233 acquired NP while admitted. Patients who developed NP had a 2.6 higher risk (95% confidence interval: 2.1-3.0) of dying compared with those who did not develop NP. When stratified by the APACHE II index, the significant association remained at each stratum, although the strength of the association decreased as the value of the index increased. In the multivariate analysis, NP was independently associated with death in the ICU. The interaction between NP and the APACHE II index, with a negative coefficient, was also significant.

Developing NP while admitted to the ICU was independently associated with increased mortality. However, the strength of the association decreased as the severity of patient illness upon admission to the ICU increased, not influencing death of patients with severe APACHE II values.