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Methodology for Sputum Induction and Laboratory Processing
Published on: December 17, 2017
Utility of Induced Sputum in Assessing Bacterial Etiology for Community-Acquired Pneumonia in Hospitalized Children
Amanda Green1,2, Jody L Cockroft3, Robert A Kaufman4
1Department of Pediatrics, University of Tennessee Health Science Center, Memphis, Tennessee, USA.
Insights
Induced sputum (IS) testing for pediatric community-acquired pneumonia (CAP) frequently identifies bacteria, but these often reflect oral bacteria, not the lung infection. This method is insufficient for determining the bacterial cause of CAP.
Area of Science:
- Pediatric infectious diseases
- Respiratory medicine
- Diagnostic microbiology
Background:
- Bacterial testing for community-acquired pneumonia (CAP) in children has low sensitivity.
- Induced sputum (IS) is a potential method for evaluating lower respiratory tract infections.
Purpose of the Study:
- To assess the utility of induced sputum (IS) for identifying bacterial pathogens in pediatric community-acquired pneumonia (CAP).
- To compare pathogen detection rates in high-quality (HQ) versus low-quality (LQ) IS specimens.
- To evaluate the concordance of IS findings with sterile site cultures and their impact on antibiotic treatment.
Main Methods:
- Children aged 0-18 with CAP were enrolled in the Etiology of Pneumonia in the Community (EPIC) study.
- Induced sputum (IS) was collected after hypertonic saline nebulization.
- IS quality was determined by Gram stain; pathogen prevalence was compared between HQ and LQ samples.
- Concordance with other diagnostic methods and length of stay (LOS) based on antibiotic treatment were analyzed.
Main Results:
- Of 977 children, 916 produced IS; 174 (19%) yielded high-quality (HQ) specimens.
- HQ IS identified pathogens more often than LQ IS (64% vs. 44%, P < .01).
- IS pathogens matched sterile site cultures in only 21% of cases; LOS was similar regardless of antibiotic concordance.
Conclusions:
- Bacterial pathogens are frequently isolated from pediatric IS, irrespective of radiographic CAP or specimen quality.
- IS pathogen detection often reflects oropharyngeal carriage rather than true infection.
- Induced sputum is insufficient for definitively determining the bacterial etiology of pediatric CAP.
Background:
Diagnostic testing for bacterial etiology of community-acquired pneumonia (CAP) is insensitive. Induced sputum (IS) is an attractive option for the evaluation of the lower respiratory tract.
Methods:
Children aged 0-18 years with CAP were enrolled in the Etiology of Pneumonia in the Community (EPIC) study between 2010 and 2012. Blood and respiratory specimens were assessed by culture and polymerase chain reaction (PCR). The radiographic CAP was determined by a study radiologist. Sputum was induced with hypertonic saline. IS specimen was high quality (HQ) if Gram stain showed >25 white blood and <10 epithelial cells per low-powered field; all others were low quality (LQ). We compared IS pathogen prevalence between HQ and LQ IS, and by radiographic pneumonia. Pathogen concordance with EPIC etiology was assessed. Length of stay (LOS) was compared by receipt of IS pathogen-concordant antibiotics.
Results:
Out of 977 children, 916 (94%) children enrolled in Memphis, Tennessee, produced IS; 794 (87%) had radiographic CAP and 174 (19%) were HQ. HQ IS yielded pathogenic bacteria more often than LQ (64% vs 44%; P < .01); however, pathogens were isolated at similar rates in HQ IS in patients with and without radiographic CAP (64% vs. 63%; P = .6). Pathogens from study specimens matched an IS pathogen in only 9/42 (21%) patients with radiographic CAP. Median LOS was similar among patients with radiographic CAP regardless of receipt of IS pathogen-concordant antibiotics (3.1 days), non-pathogen-concordant antibiotics (2.7 days), or no antibiotics (3.2 days; P = .5).
Conclusions:
Bacterial pathogens were isolated from most IS cultures regardless of radiographic CAP and quality of IS. IS cultures infrequently corresponded with sterile site cultures. Isolation of pathogens from pediatric IS reflects oropharyngeal carriage and is insufficient to determine bacterial etiology of CAP.
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