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Is protected specimen brush a reproducible method to diagnose ICU-acquired pneumonia?
J F Timsit1, B Misset, S Francoual
1Intensive Care Unit, Hôpital Saint Joseph, Paris, France.
Unlabelled:
Protected specimen brush (PSB) is considered to be one of the standard methods for the diagnosis of ventilator-associated pneumonia, but to our knowledge, intraindividual variability in results has not been reported previously.
Purpose:
To compare the results of two PSB performed in the same subsegment on patients with suspected ICU-acquired pneumonia (IAP).
Study Design:
Between October 1991 and April 1992, each mechanically ventilated patient with suspected IAP underwent bronchoscopy with two successive PSB in the lung segment identified as abnormal on radiographs. Results of the two PSB cultures were compared using 10(3) cfu/ml cutoff for a positive result. Four definite diagnoses were established during the follow up: definite pneumonia, probable pneumonia, excluded pneumonia, and uncertain pneumonia.
Population:
Forty-two episodes in 26 patients were studied; 60 percent of patients received prior antibiotic therapy. Thirty-two microorganisms were isolated from 24 pairs of PSB. Definite diagnosis was definite pneumonia in 7, probable pneumonia in 8, excluded pneumonia in 17, and uncertain pneumonia in 10 cases.
Results:
The PSB recovered the same microorganisms and argued for a good qualitative reproducibility. The distinction of positive and negative results on the basis of the 10(3) cfu/ml classic threshold was less reproducible. For 24 percent of the microorganisms recovered and in 16.7 percent of episodes of suspected IAP, the two consecutive samples gave results spread out on each side of the 10(3) cfu/ml cutoff. Discordance was higher when definite diagnosis was certain or probable than when diagnosis was excluded (p = 0.015). There was no statistical effect of the order of samples between the two specimens for bacterial index and microorganism concentrations.
Conclusion:
These findings argue for the poor repeatability of PSB in suspected IAP and question the yield of the 10(3) cfu/ml threshold. In attempting to diagnose IAP, the results of PSB must be interpreted with caution considering the intraindividual variability.
Insights
Protected specimen brush (PSB) testing for ventilator-associated pneumonia shows poor repeatability. Results vary significantly between two samples from the same patient, questioning the reliability of the standard 10(3) cfu/ml cutoff for diagnosis.
Area of Science:
- Critical Care Medicine
- Infectious Diseases
- Pulmonary Medicine
Background:
- Protected specimen brush (PSB) is a standard diagnostic method for ventilator-associated pneumonia (VAP).
- Intraindividual variability in PSB results has not been previously reported.
- Accurate diagnosis of VAP is crucial for appropriate patient management and antibiotic stewardship.
Purpose of the Study:
- To compare the results of two successive PSB samples taken from the same lung subsegment.
- To evaluate the intraindividual variability of PSB in patients with suspected ICU-acquired pneumonia (IAP).
Main Methods:
- Bronchoscopy with two sequential PSB was performed on mechanically ventilated patients with suspected IAP.
- PSB cultures were analyzed using a 10(3) colony-forming units/ml cutoff for positive results.
- Diagnoses were categorized as definite pneumonia, probable pneumonia, excluded pneumonia, or uncertain pneumonia.
Main Results:
- While microorganisms were qualitatively reproducible, quantitative results around the 10(3) cfu/ml cutoff showed poor reproducibility.
- 24% of recovered microorganisms and 16.7% of suspected IAP episodes had results straddling the cutoff.
- Discordance was significantly higher in cases of definite or probable pneumonia compared to excluded pneumonia (p=0.015).
Conclusions:
- The study demonstrates poor repeatability of PSB for diagnosing IAP, highlighting significant intraindividual variability.
- The standard 10(3) cfu/ml threshold for PSB results may be unreliable.
- Results of PSB for IAP diagnosis should be interpreted with caution due to observed variability.