This presentation will demonstrate how on-site qPCR has both a strong positive and negative predictive value and is an advantageous tool to minimize Legionella risk. 

1. It will demonstrate using a recently published study that Legionnaires' disease is common and underdiagnosed and how the disease prevalence may be attributed to the current methods used to detect Legionella in water systems.

2.  For the first two case study, it will highlight the inaccuracies when using culture to determine Legionella quantification. It will demonstrate that performing on-site qPCR can minimize risk and prove the effectiveness of decontamination procedures.

3. For the third case study, completed at a healthcare facility, it was show that on-site qPCR when compared to traditional qPCR had superior positive predictive value relative to laboratory culture. 

Shaimaa Ahmed, PhD. 

HVAC cooling towers are a significant source of Legionella bacteria, the causative agent of Legionnaires’ disease (LD). In a recent study, the frequency of Legionnaires’ disease (LD) was assessed among pneumonia cases treated at a large community hospital over a summer season. Of the 33 patients tested, 9 (28%) were positive for Legionella. Three sets of the 9 Legionella cases exhibited spatiotemporal clustering indicative of LD outbreaks. It has been suggested that the prevalence of the disease may be linked to the methods used to quantify Legionella in water systems. The current standard for testing is laboratory culture which is prone to inaccuracies due to sample processing, and the requirement for shipping. On-site qPCR is not susceptible to these effects and offers a rapid sample-to-result turnaround time. We describe three case studies tested by both on-site qPCR and laboratory culture that highlight the advantages of on-site qPCR in determining the presence of Legionella in water systems. In all three cases, laboratory culture produced inconsistent or inaccurate results. Two case studies illustrate the value of a rapid on-site qPCR detection system for the monitoring and quantification of Legionella in HVAC cooling towers, as well as confirmation of decontamination procedures. Both of these case studies highlight the negative predictive value for qPCR. In the third case study, completed at a healthcare facility, it was shown that on-site qPCR when compared to traditional qPCR had superior positive predictive value relative to laboratory culture. Overall, these case studies indicate that on-site qPCR is a powerful tool to minimize risk to individuals as it has a strong positive and negative predictive value.

Shaimaa Ahmed is the R&D Leader for Spartan’s environmental testing division. She holds a PhD in Pharmacology and Toxicology from the University of Toronto, Canada.