Kahn and Jones evaluated 75 patients for the presence of bacterial lower respiratory tract infection. Thirteen patients with bacterial pneumonia were included; unfortunately, five patients had a hematologic malignancy and two had a lung abscess. Of the remaining six patients, three were receiving antibiotics when subjected to bronchoscopy. The authors suggest a cutoff point of 105 cfu/ml, but the inhomogeneity of the population studied prevents interpretation of these data with accuracy.
With regard to the definition of the best cutoff point for TPC and BAL, several considerations may be raised. First, the optimal cutoff point for these techniques must be determined separately in different populations with pneumonia such as CAP, nosocomial pneumonia, mechanical ventilation-associated pneumonia, or immunosuppressed patients with pneumonia since the bacterial agents involved are different in each case, and the significance of the colony counts differs in each class of pneumonia. Secondly, it must be kept in mind that with the brush 0.001 to 0.01 ml of secretion can be obtained. As the brush sample is diluted in 1 ml of fluid, a 100- to 1,000-fold dilution before plating occurs. On the other hand, BAL samples a larger area of the lung, and only 1 ml of the recovered fluid is plated. This small volume of fluid reflects at least a 100-fold dilution of lung secretions, depending on the amount of saline solution instilled.