• Valeria Giunta, Miquel Ferrer, Mariano Esperatti, Otavio T Ranzani, Lina Maria Saucedo, Gianluigi Li Bassi, Francesco Blasi, and Antoni Torres.
• Servei de Pneumologia, Institut del Torax, Hospital Clinic, IDIBAPS, Universitat de Barcelona, Barcelona, Spain.
• Crit. Care Med.. 2013 Sep 1;41(9):2133-43.

ObjectivesThe 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.DesignProspective observational study.SettingICUs of a university teaching hospital.PatientsWe prospectively collected 270 consecutive patients with ICU-acquired pneumonia. Patients were clustered according to positive or negative microbiologic results.InterventionsNone.Measurements And Main ResultsWe 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.ConclusionsAlthough 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.

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