Microbial content of aerosols produced from suspensions exposed to megahertz frequency ultrasound.

A piezo-electric bowl transducer was used to generate aerosols by focusing ultrasound in the frequency range 1-7 MHz at a liquid/air interface. Atomization at the liquid surface and the production of a fountain contributed to aerosol formation. When the liquid consisted of suspensions of representatives from the viral, bacterial, and yeast groups of micro-organisms (covering a 0.2-11.5 microns size range) living organisms were isolated from the aerosols at all frequencies. The fountains were implicated as a major source of air-borne micro-organisms because significant numbers of isolates were obtained in the presence of fountains but in the absence of obvious atomization, and theoretical predictions make the sizes of droplets arising from atomization at the higher frequencies too small to have carried some of the larger organisms.