Bacterial colonization of ultrasonic nebulizers: implications for frequency of circuit changing.

We conducted a prospective study of 50 consecutive postoperative patients over a 5-month period to characterize the bacterial contamination of ultrasonic nebulizers (USNs) after 24, 48, and 72 hours (h) of use.Samples of the USN effluent mist and reservoir fluid were cultured and the results were correlated with clinical data from patient records, especially indications of pneumonia or related infections.Two thirds of the USNs were bacteria-free at the three times they were tested. After 24 h, cultures of the mist revealed bacterial growth in only 1 of the 50 patients. After 48 and 72 h, cultures of the mist showed bacterial growth in 6 instances (12%). Colonization of the reservoir fluid was also limited to 1 patient after 24 h. Reservoir-fluid cultures were positive in 10% of the USNs at 48 h and in 18% at 72 h. No clinically significant signs of pneumonia developed in any patient.These results suggest that colonization of USNs is minimal during the first 72 h of use by postoperative patients with uncomplicated clinical courses and that clinical consequences are unlikely in such patients even when the USN is found to have been colonized. Although the Centers for Disease Control has recommended daily changing of USN circuits, this practice may not be warranted in all clinical settings. Further studies are needed to determine the colonization of USNs used by patients with more complicated clinical courses.