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Paper Topic:

Legionnaire`s disease

Legionnaire`s disease

Introduction

Since the identification of Legionella two decades ago , a significant amount of information has accumulated concerning the microbiology epidemiology , clinical manifestations , control , and therapy of infections caused by these organisms . The number of species in the genus Legionella has increased dramatically . Legionella is considered to be responsible for 2-13 of cases of community-acquired pneumonia requiring hospitalization (Brieman and Butler , 1998 . The various Legionella species can cause two distinct diseases : a severe form of pneumonia known as Legionnaire disease or a less serious , influenza-like illness known as

Pontiac fever , which is generally recognized only during those outbreaks in which a cluster of cases of Legionella pneumonia sparks an epidemiologic investigation that uncovers these less serious infections

Microbiology

The organism is a Gram-negative bacillus . There are currently 42 described species of Legionellae representing 64 serogroups in the family (Benson and Fields , 1998 . Legionellaceae and the genus Legionella . The phenotypic characteristics of Legionellae are defined by growth requirements , and biochemical characteristics including fatty acid analysis and ubiqui analysis , protein pros , carbohydrate analysis , serology , monoclonal antibodies , and molecular techniques (DNA-DNA hybridization . L . pneumophila is a facultative intracellular pathogen that invades and replicates within free-living protozoa (i .e amoeba ) and mammalian cells (Benson and Fields , 1998 . Within natural environments , L . pneumophila can persist as a free-living microbe , but it replicates exclusively as an intracellullar parasite within amoeba L . pneumophila causes Legionnaire 's disease by replication in alveolar macrophages and monocytes . During infection the Legionnaire 's disease bacterium survives and multiplies within a specialized phagosome that is near neutral pH and does not fuse with host lysozymes . Studies show that the regulation of macrophage resistance versus susceptibility to infection is mediated by specific genetic mechanisms . The induction of cytokines by Legionella can activate immune cells , especially T helper cells . Activated macrophages restrict the growth of Legionella (Segal and Shuman , 1998

Epidemiology

Cases can occur in clusters or sporadically from the community or in the hospital setting . The disease is much more common than previously appreciated with at least 13 000 cases estimated to occur per year in the United States (Brieman and Butler , 1998 . There may also be local environmental factors that are important and still not well defined Although immunosuppressed patients and specifically transplant patients seem to have a higher risk of developing Legionnaire 's disease , there are many more non-immunosuppressed individuals in the community who may be infected with Legionella . nvestigations into community outbreaks still find cooling towers to be a source of the Legionella

Clinical manifestation

Luttichau et al (1998 ) investigated an outbreak of Pontiac fever in children and adults , caused by a contaminated whirlpool . The authors isolated L . pneumophila serogroup OLDA from one of the children and believe that this represents the first reported culture-confirmed case of Pontiac fever . The outbreak was characterized by a short incubation period , influenza-like symptoms , and rapid recoveries , all features typical of Pontiac fever . The median incubation period for the children was shorter (43 h ) than for the adults (70 h . The median duration...

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