The Legionella species of bacteria are pathogens responsible for 1-5% of community-acquired and nosocomial pneumonia. Legionella pneumonia is not clinically distinguishable from other types of pneumonia; therefore, microbiological diagnosis is required. The purpose of this study was to determine the benefit of routinely using the polymerase chain reaction (PCR) for diagnosing Legionnaires’ disease in a clinical setting.
The urinary antigen test and PCR, a nucleic acid amplification test (NAAT), are both useful for quickly diagnosing an individual in the early stages. The former can yield test results within a half-hour, but is limited to a small number of serogroups of Legionella pneumophila and therefore has the potential of missing up to 40% of Legionnaires’ disease (LD) cases. NAATs, including PCR, are effective alternative tools for finding legionellae due to their ability to rapidly detect all species of Legionella. PCR also has the sensitivity greater than or equal to culture. False-positive results can occur, however, which has prevented the widespread use of PCR.
However, the amount of additional laboratory and microbiological tests should depend on the severity of the case. Urinary antigen testing is a frequently used method since Legionella pneumophila serogroup 1 is the most common Legionella species. However, if a negative antigen test is seen in a patient presenting with pneumonia of unknown etiology, Legionella-specific PCR should be performed as well since it could identify legionellae missed by urinary antigen.
To read more about this study, please go to the full article at the Journal of Legionella and the Law at http://www.legionlawjournal.com/2013/10/08/utility-of-real-time-pcr-for-diagnosis-of-legionnaires-disease-in-routine-clinical-practice-a-brief-overview/