Validation of a rapid diagnostic strategy for determination of significant bacterial counts in bronchoalveolar lavage samples.
BACKGROUND
Bacterial cultures of bronchoscopic samples require 1 to 2 days for results to be available for use in clinical decisions. We developed a rapid diagnostic testing strategy that is highly sensitive for screening bacteria in bronchoalveolar lavage (BAL) samples, with results available within hours of collection.


OBJECTIVE
To validate the ability of a bacterial adenosine triphosphate (ATP) assay and routine Gram stain microscopy to detect significant bacterial counts in BAL samples.


METHODS
Four hundred seventy-seven BAL samples from 319 patients suspected of having pneumonia were tested using a rapid diagnostic strategy, consisting of Gram stain and a bacterial ATP assay. Rapid results were compared with quantitative cultures with a positive cutoff of 10(4) CFU/mL or higher.


RESULTS
Significant bacterial counts were identified in 107 samples (22%). The most common etiologic agents were Staphylococcus aureus (25%), Haemophilus influenzae (17%), and Streptococcus pneumoniae (12%). The rapid test results were false negative in 5 cases (S aureus in 2, both Klebsiella pneumoniae and S aureus in 1, and Stenotrophomonas maltophilia and S pneumoniae in 1 case each). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the rapid diagnostic strategy were 95.3%, 54.9%, 37.9%, 97.6%, and 63.9%, respectively.


CONCLUSIONS
A negative result with this rapid diagnostic testing strategy rules out significant bacterial counts in BAL samples with a high degree of certainty and may allow use of narrow-spectrum antimicrobial agents or withholding of empiric antimicrobial therapy in patients suspected of having ventilator-associated pneumonia.
Laupland
Kevin B
KB
Department of Critical Care Medicine, Centre for Antimicrobial Resistance, University of Calgary, Alberta, Canada.
Church
Deirdre L
DL
Gregson
Daniel B
DB
D001431:Bacteriological Techniques / Q000379:methods; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology*; D015169:Colony Count, Microbial / Q000379:methods*; D003937:Diagnosis, Differential; D003948:Diagnostic Techniques, Respiratory System / Q000592:standards; D005260:Female; D005840:Gentian Violet; D016905:Gram-Negative Bacterial Infections / Q000175:diagnosis; D006192:Haemophilus Infections / Q000175:diagnosis; D006193:Haemophilus influenzae / Q000302:isolation & purification; D006801:Humans; D007710:Klebsiella Infections / Q000175:diagnosis; D007711:Klebsiella pneumoniae / Q000302:isolation & purification; D008297:Male; D008875:Middle Aged; D010619:Phenazines; D011008:Pneumococcal Infections / Q000175:diagnosis; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000175:diagnosis; D013211:Staphylococcus aureus / Q000302:isolation & purification; D020615:Stenotrophomonas maltophilia / Q000302:isolation & purification; D013296:Streptococcus pneumoniae / Q000302:isolation & purification
C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet