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Chapter 33 : Clinical Validation of Diagnosis of Legionella Infections
Legionella pneumophila is the etiologic agent of Legionnaires' disease, which is a very serious illness with pneumonia and a mortality of 15 to 20%. In addition to L. pneumophila, more than 40 other Legionella spp. are known (designated in this chapter as non-L. pneumophila species), of which several species have been shown to be pathogenic for humans. To improve diagnosis of Legionella infections, the authors designed a novel PCR to specifically amplify all Legionella DNA. Specific probes LPN and LSPP were used for discrimination of, respectively, L. pneumophila and non-L. pneumophila species. The sensitivity of PCR was determined by spiking bacteria in negative clinical material. The lower detection limit was found to be at least 0.1 CFU. A total of 208 samples from 208 patients clinically suspected of legionellosis were subjected to the Legionella PCR/probe procedure. Comparison of results of PCR, serology, culture, and urine antigen detection revealed that PCR-based detection of L. pneumophila, and serology in reconvalescent serum, yielded 2.8-fold more positives than Legionella culture. PCR may provide an important contribution to an early diagnosis of legionellosis. PCR is the only method suitable to diagnose non-L. pneumophila infections. Future studies could include sequencing of non-L. pneumophila PCR products to get an impression of the distribution of Legionella species in patient samples.