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Diagnosis of legionellosis
Last reviewed: 03.07.2025
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Legionellosis diagnostics is based on the isolation of L. pneumophilla culture from blood, sputum, bronchial washings, and pleural fluid. Serological diagnostics of legionellosis is performed using RIF and ELISA methods. The study of paired sera in the dynamics of the disease is of diagnostic value. The diagnostic titer in a single serum study is 1:128. Gene diagnostics is used by the PCR method.
[ Indications for consultation with other specialists
Indications for consultation with a neurologist are the development of meningoencephalitis in the acute period of the disease and signs of asthenovegetative syndrome during the recovery period; for consultation with an ENT specialist, nosebleeds; for consultation with a gynecologist, uterine bleeding.
Indications for hospitalization
The presence of intoxication in combination with symptoms of damage to the respiratory tract and central nervous system.
Differential diagnosis of legionellosis
The diagnosis of legionellosis based on clinical data can currently only be established taking into account epidemiological data. Pneumonia of legionellosis etiology should be differentiated from pneumonia of other etiologies, primarily from atypical pneumonia (ornithosis, Q fever, respiratory mycoplasmosis), as well as from pneumococcal, Haemophilus influenzae, staphylococcal, and Klebsiella pneumonia. Due to the clinical similarity of pneumonia of various etiologies, the results of microbiological and immunological studies are of decisive importance.
The clinical course of Legionnaires' disease has its own characteristics, which may be important in differential diagnosis. A dry, prolonged cough, characteristic of mycoplasma pneumonia, differs from a moderate, rare cough at the onset of Legionnaires' disease. The absence of a significant cough with extensive damage to the lung tissue distinguishes legionellosis from pneumonia of pneumococcal and Klebsiella etiology. CNS damage in legionellosis occurs much more often than in pneumonia of other etiologies.
Legionellosis may be suspected if treatment of pneumonia with cephalosporins is ineffective.