Microbial contamination of in-use ultrasonic room humidifiers

Abstract

Hypersensitivity pneumonitis or infection have been associated with the use of microbially contaminated ultrasonic humidifiers. In this study, we measured the contamination density of ultrasonic humidifiers used in such places as schools, homes, stores and beauty parlors. The water in the transducer chambers of the machines was tested. Of 20 types of machine, 13 contained 104∼105 viable bacterial cells/ml and the remainder 102∼103 cells/ml. Ultrasonic humidifiers contaminated at a concentration of 104∼105 cells/ml have been reported to induce hypersensitivity pneumonitis, indicating that over half of the in-use machines tested could be a source of this disorder. The primary contaminants were glucose nonfermentative gram-negative bacilli such as Pseudomonas spp. The heavy contamination of ultrasonic humidifiers was mainly attributed to the difficulty in keeping these machines clean. © 1990, Japanese Society of Chemotherapy. All rights reserved.