Legionella Pneumophila Infections among Egyptian Patients: Updated Diagnostic Tests and Evaluation

Abstract

Background and study aims: Legionella pneumophila is a gram-negative bacterium, which is implicated in causing Legionnaires’ disease and Pontiac fever. This study aims at evaluating the different updated diagnostic tests of L. pneumophila infections among pneumonic patients through the detection of L. pneumophila urinary antigen testing (UAT), and quantitative Real Time PCR (RT PCR) in comparison to the gold standard test and to detect the prevalence of pneumonia caused by L. pneumophila. Patients and Method: One hundred patients with features suggestive of pneumonia and confirmed by imaging were enrolled in this study. Serum, urine and lower respiratory specimens were obtained from patients admitted to Chest and Tropical Medicine Departments, Zagazig University Hospitals. Patients were subjected to urinary antigen test, lower respiratory specimens’ cultures and q Real Time (RT) PCR for detection of L. pneumophila mip gene. Results: Prevalence of L. pneumophila in Zagazig university hospitals was 17% detected by L. pneumophila urinary antigen testing (LPUAT), 15% of samples were positive by q RT PCR based mip gene and 12 % positive by respiratory sample cultures. In comparison to respiratory sample culture, the gold standard, q RT PCR evaluation showed sensitivity 83.3%, specificity 94.3%, positive predictive value 66.7%, Negative predictive value 97.6% and accuracy of 93.0%. Conclusion: Molecular assays and UAT are promising methods that can be used in the rapid and early diagnosis of Legionella infections but they seem not to be sufficient to replace microbial cultures which must associate these techniques.