ROLE OF QUANTITATIVE CULTURES AND MICROSCOPIC EXAMINATIONS OF ENDOTRACHEAL ASPIRATES IN THE DIAGNOSIS OF PULMONARY INFECTIONS IN VENTILATEDPATIENTS

Endotracheal aspirates (EA) from 20 intubated patients in a surgical i ntensive care unit (mean ventilation time/patient = 16.5 days) were in vestigated serially by performing quantitative cultures using growth o f 10(5) cfu/mL as a cut-off point. microscopic examinations were made using Giemsa's stain for polymorphonuclear neutrophils (PMN). The spec trum of pathogens encountered was determined and compared with clinica l data to distinguish colonization from infection of the lower respira tory tract. Out of 301 EA cultures, 156 (51.8%) were positive and 145 (48.2%) were below the cut-off point. Counts of PMN were significantly higher in samples which gave positive cultures. Seventy-five differen t bacterial strains were isolated (64% were Gram-negative bacilli). Se venteen patients (85%) were colonized with Gram-negative bacteria. Nin e patients (45%) developed nosocomial pneumonia (NP), five (25%) had n o signs of pneumonia, and six (30%) had an uncertain status. Main caus ative agents for NP were Pseudomonas aeruginosa, Enterobacteriaceae an d Staphylococcus aureus. Quantitative EA cultures had a sensitivity of 81.5%, a specificity of 64.8%, a positive predictive value of 55% and a negative predictive value of 87%. Our results suggest that EA quant itative cultures (cut-off value 10(5) cfu/mL), species identification and microscopic examination of EA may help to differentiate tracheobro nchial colonization and infection, especially when bronchoscopic techn iques are not available.