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Chapter 3 : Diagnostics and Clinical Disease Treatment: Usefulness of Microbiological Diagnostic Methods for Detection of Legionella Infections
Diagnostics and Clinical Disease Treatment: Usefulness of Microbiological Diagnostic Methods for Detection of Legionella Infections, Page 1 of 2< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555815660/9781555813901_Chap03-1.gif /docserver/preview/fulltext/10.1128/9781555815660/9781555813901_Chap03-2.gif
Microbiological diagnostic methods play the key role in establishing the etiological diagnosis since the clinical presentation is not specific for Legionella infections. Currently available are culture, urinary antigen detection, direct fluorescent antigen testing, detection of nucleic acid, and serology. Culture is still the gold standard among the diagnostic methods for Legionella infections. The sensitivity of culture for the diagnosis of Legionnaire's disease has been estimated to be in the range of 11 to 65% in retrospective studies usually performed in reference laboratories. The most important technique for the identification of legionellae in the clinical laboratory is the serological characterization of isolated strain. The antigen excreted with urine has been characterized as heat-stable and resistant to enzymatic cleavage with a molecular weight of about 10 kDa. The advantages of urinary antigen detection are obvious: specimens are easy to obtain and can be investigated repeatedly; antigenuria is detectable very early and, therefore, often gives the first evidence for Legionella infection. Direct fluorescent antibody (DFA) testing of respiratory specimens is a rapid method for the detection of Legionella antigen. The excretion of DNA fragments in the urine is described for several bacterial pathogens, suggesting the suitability of urine PCR for the detection of Legionella DNA. The indirect fluorescent antibody (IFA) test is the only method for antibody detection that has been evaluated and standardized. None of the diagnostic tests presently available offers the desired quality with respect to sensitivity and specificity. Therefore, the standard technique is to use several diagnostic tests in parallel.