Quantitative tracheal bacteriologic and cytologic studies in patients with long-term tracheostomies.

Quantitative aerobic and anaerobic cultures were performed on 28 tracheal aspirates from 16 clinically stable patients with tracheostomies. There were an average of six isolates per specimen, and the mean bacterial concentration was 106.9 organisms per milliliter. The numerically dominant bacteria were aerobic and facultative gramnegative bacilli. Anaerobic bacteria were recovered from just nine specimens (32 percent); and, when present, these organisms were found in relatively low concentrations. Repeat cultures obtained 30 to 60 days later from the same patients showed substantial changes in flora, but the numerically dominant species tended to persist. Cultures of saliva and throat swabs collected at the time of tracheal aspiration showed that there was little correlation between the bacteriologic findings from the upper and lower airways. Cytologic studies indicated a mean of 12,900 cells per cubic millimeter of tracheal aspirate, with polymorphonuclear leukocytes being the predominant forms. No correlation could be found between the concentrations of polymorphonuclear leukocytes and quantitative bacterial counts. These studies indicate that tracheal aspirates from patients with stable tracheostomies harbor a complex, predominantly aerobic flora which is subject to change and bears little relationship to the flora of the adjacent upper airways. Our results also suggest that neither quantitative bacterial cultures nor cytologic analysis of these specimens would be helpful in distinguishing colonization from overt infection requiring antibiotic treatment.