Legionellosis overview

Jump to navigation Jump to search

Legionellosis Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Legionellosis from other Diseases

Epidemiology and Demographics

Risk Factors

Natural History, Complications and Prognosis

Diagnosis

History and Symptoms

Physical Examination

Laboratory Findings

Chest X Ray

CT

Other Diagnostic Studies

Treatment

Medical Therapy

Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Legionellosis overview On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

American Roentgen Ray Society Images of Legionellosis overview

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Legionellosis overview

CDC on Legionellosis overview

Legionellosis overview in the news

Blogs on Legionellosis overview

Directions to Hospitals Treating Legionellosis

Risk calculators and risk factors for Legionellosis overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Legionellosis is an infectious disease caused by Legionella species, a pleomorphic, aerobic, catalase-positive, oxidase-positive, non-spore-forming, non-capsulated, motile, Gram-negative bacteria. The majority of cases of legionellosis are reported between the Summer and early Fall (between June and October). Approximately 8,000-18,000 individuals are hospitalized annually in the USA for Legionnaires' disease with a case fatality rate ranging between 10% to 35%. Legionellosis may be classified into three types based upon the affected organ systems and the clinical presentation: pulmonary infection (Legionnaires' disease), extrapulmonary infection, and Pontiac fever. Legionella is usually transmitted by aerosol droplets when individuals breathe in contaminated mist or vapor (e.g. whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems). L. pneumophila is an intracellular parasite that can invade and replicate intracellularly. In Legionnaires' disease, the majority of exposed patients do not develop any symptoms. Patients who develop clinical manifestations usually report pneumonia-like symptoms that worsen at 4 to 6 days following onset of symptoms and eventually resolve by day 5 to 10 of symptom-onset. Approximately 1% to 35% of individuals progress to develop Legionnaires'-related complications and death. Complications of Legionnaires' disease include empyema, lung failure, acute kidney injury, endocarditis, neurological disease, septic shock, and multisystem organ failure. The prognosis is generally good for healthy patients, but patients with co-morbidities at higher risk of developing complications and death. In contrast, Pontiac fever has a high attack rate but is associated with mild flu-like symptoms that resolve within 1 to 2 days and is almost always self-limited without any complications. The most important risk factor in the development of legionellosis is recent exposure to either aerosolized water or contaminated water. Other risk factors include old age, concomitant lung disease, active smoking status, and immunosuppression. Urine antigen testing in the first-line diagnostic method. Culture of the lower respiratory secretion is the gold standard for detecting Legionnaires' disease. Imaging may also be indicated among patients with Legionnaires' disease. Pharmacologic medical therapy is indicated in Legionnaires' disease, but not in Pontiac fever. The preferred regimens for both mild and moderate-to-severe Legionnaires' disease include either azithromycin or a fluoroquinolone. Patients with who develop legionellosis-related complications may require other or additional pharmacologic agents. There is no vaccine against legionellosis, and antibiotic prophylaxis is not effective.

Historical Perspective

Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia. On January 18, 1977 the causative agent was identified as a previously unknown bacterium, subsequently named Legionella. Outbreaks of Legionnelosis are listed below in chronological order.

Classification

Legionellosis may be classified into three types based upon the affected organ systems and the clinical presentation: pulmonary infection (Legionnaires' disease), extrapulmonary infection, and Pontiac fever. Legionellosis may also be classified based on the infectious species responsible for the disease.

Pathophysiology

Legionella is usually transmitted by aerosol droplets when individuals breathe in contaminated mist or vapor (e.g. whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems). L. pneumophila is an intracellular parasite that can invade and replicate intracellularly. Legionella is internalized using pseudopods and protects itself in a membrane-bound vacuole that does not fuse with lysosomes.

Causes

L.pneumophila is a ubiquitous aquatic organism that thrives in warm environments (32°- 45°C). L. pneumophila is pleomorphic, aerobic, catalase-positive, oxidase-positive, non-spore-forming, non-capsulated, motile, Gram-negative bacteria. Although Legionella is categorized as a Gram-negative bacterium, it stains poorly to Gram stain due to its unique lipopolysaccharide-content in the outer psuedospamodulating leaflet of the outer cell membrane.

Differential Diagnosis

Legionellosis must be differentiated from other causes of fever, dyspnea, cough, and sputum production, such as bacterial pnuemonia, viral pneumonia, and other causes of atypical pnuemonia.

Epidemiology and Demographics

The majority of cases of legionellosis are reported between the Summer and early Fall (between June and October). Approximately 8,000-18,000 individuals are hospitalized annually in the USA for Legionnaires' disease with a case fatality rate ranging between 10% to 35%. The median case-patient age is 61 years, and the male to female ratio is 1.8 to 1.

Risk Factors

The most important risk factor in the development of legionellosis is recent exposure to either aerosolized water or contaminated water. Other risk factors include old age, concomitant lung disease, active smoking status, and immunosuppression.

Natural History, Complications and Prognosis

In Legionnaires' disease, the majority of exposed patients do not develop any symptoms. Patients who develop clinical manifestations usually report pneumonia-like symptoms that worsen at 4 to 6 days following onset of symptoms and eventually resolve by day 5 to 10 of symptom-onset. Approximately 1% to 35% of individuals progress to develop Legionnaires'-related complications and death. Complications of Legionnaires' disease include empyema, lung failure, acute kidney injury, endocarditis, neurological disease, septic shock, and multisystem organ failure. The prognosis is generally good for healthy patients, but patients with co-morbidities at higher risk of developing complications and death. In contrast, Pontiac fever has a high attack rate but is associated with mild flu-like symptoms that resolve within 1 to 2 days and is almost always self-limited without any complications.

Diagnosis

History and Symptoms

Legionellosis may manifest with either Legionnaires' disease or Pontiac Fever. Legionnaires' disease is more severe and typically manifests with fatigue, malaise, symptoms of pneumonia (fever, dyspnea, chest pain, and cough) and occasionally diarrhea and nausea. In contrast, Pontiac fever is a milder form of respiratory flu-like disease (fever and cough) but does not result in pneumonia. Patients with legionellosis often report a recent history of travel, hospitalization, exposure to contaminated water, or exposure to healthcare settings.

Physical Examination

Physical examination may be remarkable for fever, as well as consolidation and crackles on pulmonary auscultation. Patients with advanced disease may develop neurological signs, including altered mental status, weakness, and ataxia.

Laboratory Findings

Laboratory abnormalities in Legionnaries' disease include leukocytosis with relative lymphopenia, hyponatremia, hypophosphatemia, and elevated levels of AST/ALT, CPK, ESR, CRP, LDH, and ferritin. Urine antigen testing in the first-line diagnostic method. Culture of the lower respiratory secretion is the gold standard for detecting Legionnaires' disease.

Chest X ray

Common chest x-ray findings in Legionnaires' disease include consolidation and pleural effusion. There are usually no chest x-ray findings in Pontiac fever.

CT

In Legionnaires' disease, chest CT findings may include bilateral, multiple affected segments and peripheral lung consolidation with ground glass opacity. There are usually no chest CT findings in Pontiac fever.

Other Diagnostic Studies

Additional studies are not required for the diagnosis of legionellosis.

Treatment

Medical Therapy

Pharmacologic medical therapy is indicated in Legionnaires' disease. The preferred regimens for both mild and moderate-to-severe pneumonia include either azithromycin or a fluoroquinolone. Patients with who develop legionellosis-related complications may require other or additional pharmacologic agents. Pontiac fever is self-limited and may be treated with symptomatic therapy only.

Prevention

There is no vaccine against legionellosis, and antibiotic prophylaxis is not effective. Travelers at increased risk for infection, such as the elderly or those with immunocompromising conditions such as cancer or diabetes, may choose to avoid high-risk areas, such as whirlpool spas.


References