Table 1.

Comparison of various sampling methods used for NHSN microbiologic thresholds

Specimen	Collectors	Site(s) sampled	Sample amt	Diluent vol	Dilution factor	Quantitative thresholda	Semiquantitative equivalentb	Comment(s)
Lung tissue	Trained physicians	Lung parenchyma	∼1.0 g	∼1.0 ml	1	≥104 g	Few-moderate or 2-3+	Often obtained postmortem, is not representative of all patients
Bronchoscopicc protected specimen brushing	Trained physicians	Bronchioles	0.001–0.01 ml	1.0 ml	1/100–1/1,000	≥103 ml	Rare-few or 1-2+	Low-volume sampling restricts utility
Bronchoscopic bronchoalveolar lavage fluid	Trained physicians	Bronchioles and alveoli	∼1 ml	10–100 ml	1/10–1/100	≥104 ml	Few-moderate or 2-3+	Adequate volume for multiple analyses, including microscopy
Nonbronchoscopic protected specimen brushing	Respiratory therapists or trained personnel	Bronchioles	0.001–0.01 ml	1.0 ml	1/100–1/1,000	≥103 ml	Rare-few or 1-2+	Low-volume sampling restricts utility
Nonbronchoscopic bronchoalveolar lavage fluid	Respiratory therapists or trained personnel	Bronchioles and alveoli	∼1 ml	10–100 ml	1/10–1/100	≥104 ml	Few-moderate or 2-3+	Comparable to bronchoscopic alveolar lavage but often lower in lavaged volume
Endotracheal aspirate	Respiratory therapists or nurses	Tracheal secretions	1–10 ml	1–10 ml	1–1/10	≥105 ml	Moderate-numerous or 3-4+	Easily obtained; primarily reported semiquantitatively with microscopy

^aNumber of colonies meeting threshold value varies with calibrated loop volume.

^bAssuming an ∼0.01-ml inoculum and a quadrant streak method with the following observations: rare or 1+ is growth in first quadrant, few or 2+ is growth in second quadrant, moderate or 3+ is growth in third quadrant, and numerous or 4+ is growth in fourth quadrant.

^cBronchoscopic sampling is performed via fiber optic bronchoscopy and incurs greater costs but allows targeted sampling.