Decision-Making Around Positive Tracheal Aspirate Cultures: The Role of Neutrophil Semiquantification in Antibiotic Prescribing

Abstract

Ventilator-associated infections are a major contributor to antibiotic use in the PICU. Quantitative or semiquantitative assessment of neutrophils (microscopic purulence) is routinely reported in positive cultures from tracheal aspirates. The role of microscopic purulence in guiding antibiotic therapy or its association with symptoms of ventilator-associated infections is less described in children. We examine microscopic purulence as an independent predictor of antibiotic use for positive tracheal aspirate cultures in the PICU. Retrospective cohort study. Tertiary care pediatric hospital. Children admitted to the PICU, neuro-PICU, or cardiac PICU with a positive tracheal aspirate culture from January 1, 2016, to December 31, 2016. None. Positive tracheal aspirate cultures were reviewed. The outcome variable was antibiotic treatment that targeted the positive tracheal aspirate culture. The predictor variable was microscopic purulence, defined as moderate or many neutrophils on Gram stain report. Competing predictors included demographics, comorbidities, vital signs changes, respiratory support, and laboratory values. Of 361 positive cultures in the cohort, 81 (22%) were treated with antibiotics. Positive cultures with microscopic purulence were targeted for therapy more frequently (30% vs 11%). Microscopic purulence was the strongest predictor for antibiotic therapy (odds ratio, 3.3; 95% CI, 1.6-6.8) compared with fever (odds ratio, 2.0; 95% CI, 1.0-4.1) or increased respiratory support (odds ratio, 2.3; 95% CI, 1.2-4.3). There was no significant variation in symptomatology between microscopic purulence reported as moderate or many versus other (e.g., fever -24% vs 22%, increased respiratory support -36% vs 28%). Microscopic purulence was less prevalent with longer ventilator durations at the time of sampling. Microscopic purulence was an independent predictor of antibiotic therapy for positive tracheal aspirate cultures in our PICUs. However, microscopic purulence was not associated with clinical symptomatology.