Diagnostic accuracy of protected specimen brush and bronchoalveolar lavage in nosocomial pneumonia: impact of previous antimicrobial treatments

Abstract

Objective: To determine whether the diagnostic accuracy of bronchoscopy samples in patients with suspected ventilator-associated pneumonia is affected by prior antibiotic treatment given for a previous infection, and/or by antibiotic treatment recently started to treat suspected ventilator-associated pneumonia.

Design: Study of critically ill patients.

Setting: Intensive care unit in a university hospital.

Patients: Sixty-three episodes of suspected ventilator-associated pneumonia were prospectively evaluated. Based on prior antibiotic treatment, three groups were defined: no antibiotic group (no previous antibiotic treatments), n = 12; current antibiotic group (antibiotic treatment initiated >72 hrs earlier), n = 31; and recent antibiotic group (new antibiotic treatment class started within the last 24 hrs), n = 20.

Interventions: Fiberoptic bronchoscopy with quantitative protected specimen brush cultures, bronchoalveolar lavage cultures, and intracellular organism counts of bronchoalveolar lavage cells.

Measurements and main results: The diagnosis of ventilator-associated pneumonia was made in 35 cases, based on histology (n = 2), cavitation (n = 2), blood cultures (n = 4), or outcome under appropriate antibiotic treatment (n = 27). The discriminative value of the tests, based on the area under the receiver operating characteristic curve, was high (> or =0.85) in both current antibiotic treatment and recent antibiotic treatment patients. Sensitivities for a 5% intracellular organism count of bronchoalveolar lavage cells, a protected specimen brush culture threshold of 10(3) colony-forming units (cfu)/mL, and a bronchoalveolar lavage culture threshold of 10(5) cfu/mL were as follows, respectively, in the three groups: 0.71, 0.88, and 0.71 (no antibiotic treatment group); 0.5, 0.77, and 0.83 (current antibiotic group); and 0.67, 0.40, and 0.38 (recent antibiotic group). Specificity was consistently > or =0.9. In the recent antibiotic group, protected specimen brush and bronchoalveolar lavage cultures had lower sensitivities (p < .05), and the best threshold values for these two tests were 10(2) cfu/mL and 10(3) cfu/mL, respectively.

Conclusions: After recent introduction of an antibiotic treatment for suspected ventilator-associated pneumonia, protected specimen brush and bronchoalveolar lavage culture thresholds must be decreased to maintain good accuracy. In contrast, current antibiotic treatment prescribed for a prior infectious disease does not modify the diagnostic accuracy of protected specimen brush or bronchoalveolar lavage.