Methodologies for quantifying culturable, viable, and total Legionella pneumophila in indoor air.

Legionella pneumophila, aerosolized from numerous indoor facilities (e.g., shower heads, hot tubs, spas), may cause Pontiac fever (PF) and lethal pneumonia named Legionnaires' disease (LD) in humans. Reliable methods on quantitative exposure assessment of this bioaerosol are essential for the prevention of PF and LD. Coupled with culture, ethidium monoazide with qPCR, and qPCR assays, the collection efficiency for culturable, viable, and total L. pneumophila was assessed by means of filtration sampling (IOM with gelatin filter and cassette with polycarbonate filter) and liquid-based sampling methods (BioSampler, AGI-30, MAS-100 sampler with Tween mixture and deionized water (DW)). Results show IOM/gelatin filter was comparable to cassette/polycarbonate filter (P = 0.33) and performed greater than all of tested liquid-based methods for total cell collection. On the other hand, IOM/gelatin filter obtained greater efficiencies than cassette/polycarbonate filter by a factor of 3.8-8.6 for viable cells (P = 0.0006) and two orders of magnitude for culturable cells (P = 0.00002). Further comparison between liquid impingement and filtration methods indicates the sampling by IOM/gelatin filter, AGI-30, and BioSampler with DW were the most appropriate for viable cells, while culturable cells were collected most efficiently by BioSampler/DW with periodical replenishment during the sampling. This study recommends the most suitable methodologies for quantifying culturable, viable, and total Legionella pneumophila in indoor air. By using appropriate sampling and analytical methods, the residents and building owners are able to obtain the reliable data and further characterize the exposure risk and/or intervention efficacy against L. pneumophila. Moreover, the adoption of suitable monitoring methods also assists the investigators to explore the sources linked to PF and LD during the outbreaks. Considering reliable microbial monitoring is fundamental for epidemiological survey and risk assessment, the present information should be taken into account in assessing L. pneumophila indoors.