Purpose. To measure the aerosolization of Mycobacterium avium subspecies hominissuis and Mycobacterium abscessussubspecies abscessus from ultrasonic humidifiers.

Methodology. An ultrasonic humidifier was filled with sterile tap water and inoculated with water-acclimated cells of either the M. avium or M. abscessus strains to achieve a range of densities similar to those of mycobacteria found in drinking waters. During operation of the humidifier, aerosols were collected using an Andersen 6-Stage Cascade Sampler.

Results. Cells of the M. avium and M. abscessus strains were readily aerosolized and recovered in particles (1–5 µm diameter); small enough to enter the furthest reaches of the human lung. Aerosolization of M. abscessus was significantly reduced in the presence of a normal drinking water bacterial flora. Significantly greater numbers of M. avium cells were aerosolized from high-density suspensions (1200 c.f.u. ml), than from low-density (120 c.f.u. ml) and very low-density (12 c.f.u. ml) suspensions.

Conclusions. This report documents the potential for M. avium subspecies hominissuis and M. abscessus subspecies abscessus cells in drinking water to be aerosolized from one type of portable humidifier; an ultrasonic humidifier. Care should be taken in using an ultrasonic humidifier where an individual at risk for mycobacterial pulmonary disease could be exposed.