Methods for Detection and Quantification of Airborne Legionellae Around Cooling Towers

Inhalation of legionellae may cause severe pneumonia and Pontiac fever in humans; however, comprehensive field evaluations using various bioaerosol monitoring techniques are lacking. The performance of samplers for legionellae collection has been investigated in a chamber setting. This study further assessed the capabilities of two filter-based (cassette/polycarbonate filter and IOM/gelatin filter), two agar-based (Andersen one-stage sampler and MAS-100/A), and four liquid-based sampling methods (BioSampler, AGI-30, MAS-100/L, and SASS 2300) for monitoring culturable, viable, and total legionellae around cooling towers. The highest detection rate of culturable legionellae was obtained by the SASS 2300 (25%-31%), followed by the BioSampler (0%-23%), MAS-100/L (5%-9%), and IOM (5%), while no culturable legionellae were recovered by the other four sampling methods under the experimental conditions tested. As for the recovery of total and viable L. pneumophila and Legionella spp., the IOM consistently showed the highest efficiencies relative to the other samplers that were simultaneously tested regardless of sampling time (30-270 min), and these values were statistically comparable to those of the cassette but significantly greater than those of the other liquid- and filter-based sampling methods by 1-3 orders of magnitude (p < .05). In most cases, the biological efficiencies (calculated as a percentage of the viable cell counts to total cell counts, 19.6%-80.2%) were not significantly different between the samplers (p > .05). This study shows that viable and total legionellae can be efficiently sampled by the IOM equipped with a gelatin filter, and culturable cells may be detected more frequently by the SASS 2300.