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The Lack of Specificity of Tracheal Aspirates in the Diagnosis of Pulmonary Infection in Intubated Children

Willson, Douglas F. MD1; Conaway, Mark PhD2; Kelly, Robin RN1; Hendley, J. Owen MD3

Pediatric Critical Care Medicine:
doi: 10.1097/PCC.0000000000000106
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Abstract

Objectives: Ventilator-associated pneumonia is the first or second most commonly diagnosed nosocomial infection in the PICU. Centers for Disease Control diagnostic criteria include clinical signs or symptoms in conjunction with a “positive” tracheal aspirate, defined as more than 104 colony-forming units/mL of bacteria on quantitative culture and/or more than 25 polymorphonuclear neutrophils per low-power field on Gram stain. We hypothesized that tracheal aspirate cultures and Gram stains would not correlate with clinical signs and symptoms and would therefore not distinguish between colonization and infection.

Design: Prospective observational study.

Setting: PICU in an academic tertiary care center.

Patients: Children intubated more than 48 hours.

Interventions: Sequential tracheal aspirate quantitative cultures and Gram stains in conjunction with daily collection of concordant clinical signs and symptoms.

Measurements and Main Results: Time since intubation correlated strongly (p < 0.001) with the proportion of positive (> 104 colony-forming units/mL) tracheal aspirate quantitative cultures, but Centers for Disease Control–defined clinical signs or symptoms of ventilator-associated pneumonia, either singly or in combination, did not. Use of in-line suction catheters versus new, sterile catheters to obtain tracheal aspirates was associated with significantly greater proportion of positive tracheal aspirate bacterial cultures (p < 0.001). Most subjects had more than 25 polymorphonuclear neutrophils per low-power field on Gram stain; polymorphonuclear neutrophils on Gram stain correlated with positive bacterial culture (p = 0.04). Seventy-seven percent of the bacterial isolates detected in positive quantitative cultures were “pathogens.” Antibiotic use at the time tracheal aspirates were obtained was associated with a lower frequency of positive quantitative cultures only with antibiotic regimens that included cefepime.

Conclusions: Positive bacterial cultures of tracheal aspirates increase rapidly after intubation and usually include bacteria considered to be pathogens. Tracheal aspirate cultures and Gram stains do not appear to distinguish between infection and colonization. Antibiotic regimens that include cefepime decrease the frequency of positive cultures, but the significance of this is unclear.

Author Information

1Division of Pediatric Critical Care, Department of Pediatrics, University of Virginia Health Sciences System, Charlottesville, VA.

2Department of Public Health Sciences, University of Virginia Health Sciences System, Charlottesville, VA.

3Division of Pediatric Infectious Disease, Department of Pediatrics, University of Virginia Health Sciences System, Charlottesville, VA.

Supported, in part, by The Pendleton Pediatric Infectious Disease Fund, University of Virginia.

Dr. Willson’s institution received grant support from The Pendleton Pediatric Infectious Disease Fund, University of Virginia (This is a grant to support the laboratory of Dr. Hendley). Dr. Hendley received support from a Pendleton Infectious Disease Laboratory endowment, is employed by the University of Virginia School of Medicine, and received support for article research from the Pendleton Pediatric Infectious Disease endowment. The remaining authors have disclosed that they do not have any potential conflicts of interest.

Address requests for reprints to: Douglas F. Willson, MD, Division of Pediatric Critical Care, Children’s Hospital of Richmond at VCU, Old City Hall, 1001 E. Broad Street, Suite 205A, Richmond, VA 23219; Email: dwillson@mcvh-vcu.edu

©2014The Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies