Abstract
Legionella pneumophila is the causative agent of severe Legionnaires’ disease (LD). Although an increasing number of LD cases have been observed, published data from Slovenia are very limited and data on molecular epidemiology are even scarcer. The present retrospective study (2006–2020) reports the results of the microbiological diagnosis of LD, as well as the epidemiology and characterization of the Legionella clinical isolates. We tested urine samples from 15,540 patients with pneumonia symptoms for L. pneumophila infection by urine antigen test, of which 717 (4.6%) tested positive. Isolation of L. pneumophila was successfully performed from 88 clinical specimens, with 82 (93.2%) being identified as L. pneumophila sg 1 and six (6.8%) as L. pneumophila sg 2–14. Sequence-based typing (SBT) identified 33 different sequence types (STs), the most frequent being ST1 and ST23. Sequence type 1 mainly comprised isolates belonging to the Philadelphia subgroup, and ST23 mostly to Allentown/France. The standard SBT scheme, as well as Dresden phenotyping for L. pneumophila, presented a high diversity among isolates.
Highlights
Legionella pneumophila is a Gram-negative rod-shaped bacteria that is ubiquitous in the natural aquatic environment
In Slovenia, the use of Polymerase Chain Reaction (PCR) testing has slightly increased in recent years; it is still low, which is probably due to the fact that Legionella patients hardly produce productive coughs
In a large retrospective Belgian (Flemish) multicenter study, the added value of PCR on a respiratory specimen was compared to Urine Antigen Test (UAT) for the diagnosis of legionellosis: 37.5% (15/40) of infections of L. pneumophila were missed when UATs were performed as the sole diagnostic test [24]
Summary
Legionella pneumophila is a Gram-negative rod-shaped bacteria that is ubiquitous in the natural aquatic environment. They are facultative intracellular parasites of free living protozoa, mostly amoeba, and they can occasionally infect humans. The important route of infection is microaspiration of drinking water contaminated with Legionella or by direct incorporation into the lung during respiratory tract manipulation [2,3]. After Legionella enters the pulmonary alveoli, it is phagocytosed by macrophages, where exponential replication occurs [4]. Such an infection leads to the development of Legionnaires’ disease (LD), a severe, life-threatening pneumonia, or to a flu-like illness called Pontiac fever. A confirmed laboratory diagnosis of LD is based on the detection of L. pneumophila antigen in the urine, the isolation of Legionella spp. from lower respiratory secretions or any normally sterile site, or the demonstration of a significant rise in specific antibody level to L. pneumophila sg 1 in paired patient sera samples [7]
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