Abstract
AimTo evaluate real-time PCR as a diagnostic method for Legionnaires’ disease (LD). Detection of Legionella DNA is among the laboratory criteria of a probable LD case, according to the European Centre for Disease Prevention and Control, although the utility and advantages, as compared to culture, are widely recognised.MethodsTwo independent laboratories, one using an in-house and the other a commercial real-time PCR assay, analysed 354 respiratory samples from 311 patients hospitalised with pneumonia between 2010–15. The real-time PCR reliability was compared with that of culture and urinary antigen tests (UAT). Concordance, specificity, sensitivity and positive and negative predictive values (PPV and NPV, respectively) were calculated.ResultsOverall PCR detected eight additional LD cases, six of which were due to Legionella pneumophila (Lp) non-serogroup 1. The two real-time PCR assays were concordant in 99.4% of the samples. Considering in-house real-time PCR as the reference method, specificity of culture and UAT was 100% and 97.9% (95% CI: 96.2–99.6), while the sensitivity was 63.6% (95%CI: 58.6–68.6) and 77.8% (95% CI: 72.9–82.7). PPV and NPV for culture were 100% and 93.7% (95% CI: 91.2-96.3). PPV and NPV for UAT were 87.5% (95% CI: 83.6-91.4) and 95.8% (95% CI: 93.5-98.2).ConclusionRegardless of the real-time PCR assay used, it was possible to diagnose LD cases with higher sensitivity than using culture or UAT. These data encourage the adoption of PCR as routine laboratory testing to diagnose LD and such methods should be eligible to define a confirmed LD case.
Highlights
Legionnaires’ disease (LD) is a severe form of pneumonia and is caused by bacteria belonging to the Legionella genus
According to LD case definition [4,5], culture, a fourfold raise in Legionella pneumophila (Lp) sg1 antibodies and urinary antigen test (UAT) are the only laboratory methods considered reliable for LD case confirmation
Samples analysed by real-time PCR, culture and urinary antigen test
Summary
Legionnaires’ disease (LD) is a severe form of pneumonia and is caused by bacteria belonging to the Legionella genus. These microorganisms are ubiquitous in natural freshwater environments and can thrive in man-made water systems. A similar trend was observed in Italy, where in 2016 UAT and culture were used to diagnose 95.5% and 2.7% of cases, respectively [6]. Both culture and UAT have some limitations; culture is time consuming and has a sensitivity ranging from < 10–80% [1], UAT can be performed rapidly and with very high specificity for Lp sg, but sensitivity for non-sg antigens is very low.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
