ICU-acquired pneumonia with or without etiologic diagnosis: a comparison of outcomes

Crit Care Med. 2013 Sep;41(9):2133-43. doi: 10.1097/CCM.0b013e31828a453b.


Objectives: The impact of ICU-acquired pneumonia without etiologic diagnosis on patients' outcomes is largely unknown. We compared the clinical characteristics, inflammatory response, and outcomes between patients with and without microbiologically confirmed ICU-acquired pneumonia.

Design: Prospective observational study.

Setting: ICUs of a university teaching hospital.

Patients: We prospectively collected 270 consecutive patients with ICU-acquired pneumonia. Patients were clustered according to positive or negative microbiologic results.

Interventions: None.

Measurements and main results: We compared the characteristics and outcomes between both groups. Negative microbiology was found in 82 patients (30%). Both groups had similar baseline severity scores. Patients with negative microbiology presented more frequently chronic renal failure (15 [18%] vs 11 [6%]; p=0.003), chronic heart disorders (35 [43%] vs 55 [29%]; p=0.044), less frequently previous intubation (44 [54%] vs 135 [72%]; p=0.006), more severe hypoxemia (PaO2/FIO2: 165±73 mm Hg vs 199±79 mm Hg; p=0.001), and shorter ICU stay before the onset of pneumonia (5±5 days vs 7±9 days; p=0.001) compared with patients with positive microbiology. The systemic inflammatory response was similar between both groups. Negative microbiology resulted in less changes of empiric treatment (33 [40%] vs 112 [60%]; p=0.005) and shorter total duration of antimicrobials (13±6 days vs 17±12 days; p=0.006) than positive microbiology. Following adjustment for potential confounders, patients with positive microbiology had higher hospital mortality (adjusted odds ratio 2.96, 95% confidence interval 1.24-7.04, p=0.014) and lower 90-day survival (adjusted hazard ratio 0.50, 95% confidence interval 0.27-0.94, p=0.031), with a nonsignificant lower 28-day survival.

Conclusions: Although the possible influence of previous intubation in mortality of both groups is not completely discarded, negative microbiologic findings in clinically suspected ICU-acquired pneumonia are associated with less frequent previous intubation, shorter duration of antimicrobial treatment, and better survival. Future studies should corroborate the presence of pneumonia in patients with suspected ICU-acquired pneumonia and negative microbiology.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Biomarkers / blood
  • Cross Infection / etiology*
  • Cross Infection / microbiology
  • Female
  • Humans
  • Intensive Care Units*
  • Male
  • Medical Audit
  • Middle Aged
  • Outcome Assessment, Health Care*
  • Pneumonia, Bacterial / etiology*
  • Pneumonia, Bacterial / microbiology
  • Prospective Studies
  • Survival Analysis


  • Biomarkers