Contaminated medication nebulizers in mechanical ventilator circuits. Source of bacterial aerosols.

The contamination rates of medication nebulizers inserted into mechanical ventilator circuits were studied. Semiquantitative techniques were used to sample the reservoir fluid from in-line nebulizers during the first 24 hours after a circuit change. In the initial survey, high levels of contamination (organism concentrations above 10(3)/ml) were present in 13 (68 percent) of the 19 nebulizer reservoirs, and bacterial aerosols were produced by 10 (71 percent) of 14 nebulizers. Gram-negative bacilli were the predominant organisms isolated. Nebulizer contamination originated primarily from reflux of contaminated condensate in the ventilator circuit. When nebulizers were cleaned after each treatment, a reduced rate of contamination was found. Small bacterial aerosols (less than 3 microns in size) were produced in vitro after inoculation of nebulizers with gram-negative bacilli in concentrations isolated from in-use nebulizers. Contaminated in-line medication nebulizers generate small-particle bacterial aerosols that may increase the risk of ventilator-associated pneumonia and therefore should be cleaned or disinfected after each treatment rather than every 24 hours.