Legionnaire's Disease

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University of Oklahoma Study Abroad Microbiology in Arezzo, Italy[1]

Scanning electron microscope image of Legionella pneumophila. From: MicrobLog [2]

Etiology/Bacteriology

Taxonomy

| Domain = Bacteria
| Phylum = Proteobacteria
| Class = Gammaproteobacteria
| Order = Legionellales
| Family = Legionellaceae
| Genus = Legionella
| Species = Legionella pneumophila
| NCBI: Taxonomy Genome: Genome |

Description

Legionnaires disease is a type of pneumonia caused by the pathogenic proteobacterium Legionella pneumophila. L. pneumophila are motile, aerobic, non-spore forming, Gram-negative rods that reside in freshwater complexes with high algae and amoeba count. [12]

Clinical Features

Symptoms

Chest x-ray of Legionnaires disease patient
From: newyorkmedicaljournal.org [3]

Many of the symptoms of Legionnaires Disease are characteristic of pneumonia. Symptoms typically begin with a shortness of breath followed by a cough. A high fever, headaches, muscle aches, and malaise are other symptoms that occur with pneumonia caused by Legionella pneumophila. [2] Signs of symptoms can appear 2-14 days after being exposed to the pathogen. Many people that come into contact with Legionella pneumophila do not show symptoms. Legionnaires disease can be found in anyone; however, it is usually found in patients over 50, heavy smokers, and immunocompromised patients. [1]

Morbidity/Mortality

Due to the very low infection rate, the morbidity rate of Legionnaires disease is low as well. Although many cases do require hospitalization, patients are usually treated and cured through antibiotic treatment. Many factors such as the severity of the disease, the age of the patient, and how quickly the patient begins antibiotic treatment all contribute to the survival rate of the patient. [13] The mortality rate of Legionnaires disease is approximately 5-30% [13]. An increase in knowledge and awareness about how Legionellosis is spread has allowed the mortality rate to drop drastically worldwide in recent years. [13]

Diagnosis

On the surface, Legionnaires disease is difficult to differentiate from other types of pneumonia, there are multiple simple tests that can be run in order to determine if the symptoms are caused by Legionella pneumophila. One of the most affective and efficient tests is a urine antigen test. [12] Urine antigen tests take approximately one hour to detect the antigen produced by L. pneumophila and is 98-100% specific [13]. There are, however, a number of serotypes that cannot be detected in a urine sample. Other options in diagnosing Legionnaires disease include culturing blood or patient's sputum or detection of the pathogen in respiratory secretion through a fluorescent antibody test [12].

References

Rathore, M. and A. Alvarez. 2014. eMedicine: Legionella infection. http://www.emedicine.com/ped/topic1288.htm (Description)

Sheff, Barbara. Microbe of the month: Legionella pneumophila. Nursing2004. 34:74. http://web.a.ebscohost.com.ezproxy.lib.ou.edu/ehost/pdfviewer/pdfviewer?sid=4b6f670a-bf77-4c0a-a19a-768789fa1a0f%40sessionmgr4002&vid=2&hid=4207 (Symptoms)

Centers for Disease Control and Prevention (CDC). Legionella (Legionnaires' Disease and Pontiac Fever). Available at http://www.cdc.gov/legionella/about/index.html (Symptoms)

Centers for Disease Control and Prevention (CDC). Top 10 Things Every Clinician Needs to Know About Legionellosis. Available at http://www.cdc.gov/legionella/clinicians.html#footnotes (Morbidity)

Created by MaKenzi Burke, student of Tyrrell Conway at the University of Oklahoma.