Sero Diagnosis of Legionella Infection in Community Acquired Pneumonia (Report)
Legionnaire’s disease is acute pneumonia caused by Legionella spp., which are responsible for 2-5 per cent of community acquired pneumonia (CAP) (1). Patients are infected by inhalation of aerosols containing Legionella species or by aspiration of water contaminated with Legionella species. Over 90 per cent of Legionnaire’s disease cases are caused by Legionella pneumophila, of which 70-80 per cent belongs to serogroup type I (2,3). Diagnosis of Legionnaire’s disease is mainly based on culture, antigen detection in urine and antibody detection in serum. Of the various antibody detection methods available to detect Legionella infection, indirect immunoflourescence (IIF) assay and enzyme-linked immunosorbent assay (ELISA) are the most commonly used (3,4). Previous studies showed that serology yields good sensitivity and specificity data (5,6), four-fold or greater increase in the titre of IgG antibody is considered diagnostic. Immunoglobulin M (IgM) detection is widely used in infectious serology as it appears earlier in the course of a disease. However, despite its reported validity for the diagnosis of legionellosis (2,7,8), some investigators consider it of limited value (3,9). ELISA, which generally shows higher sensitivity and better characteristics in terms of both automation and objective measurement than immunofluorescence does, has not been thoroughly studied for the detection of IgM antibodies in legionellosis.