LEGIONELLA PNEUMONIA

Presented by: Yoseli Ventura

INTRODUCTION Legionnaires disease (LD) was recognized in 1976 after an outbreak of pneumonia at an

American Legion Convention in Philadelphia. It is caused by a type of bacteria called Legionella, which can be found usually in the

water. L pneumophila is the most frequent cause of human legionellosis and relatively common

cause of community-acquired and nosocomial pneumonia in adults. Legionellosis refers to 2 distinct clinical syndromes: Legionnaires disease & Pontiac

Fever. Most cases can be treated successfully with antibiotics, and healthy people usually recover

from infection. Immunocompromised people (individuals with cancer or AIDS) in nursing homes or hospitalized patients receiving chemotherapy for organ transplantation or cancer are more likely to become infected. Fortunately, most normal individuals are resistant to moderate doses of L. pneumophila.

MICROBIOLOGY The family Legionellaceae consists

of 50 species and includes more than 70 serogroups.

L. pneumophila is the most common species, which causes at least 80% of human infections; within this species, the serogroups 1, 4, 6 are the ones most frequently implicated.

Legionella species are aerobic, motile, catalase-positive, gram-negative bacilli that do not grow on routine bacteriologic media. Specialized media, usually buffered charcoal yeast extract media, are required for growth, which typically takes three to five days.

EPIDEMIOLOGY An estimared 8,000-18, 000 cases of Legionnaires disease are reported in

the United States each year. More than 80% of cases are sporadic throughout the year, and the rest

occur in outbreaks during summer and early fall. It is consistently reported among the top three or four most

commonly identified pathogens in community-acquired pneumonia in immunocompetent patients.

In adults, legionellosis causes 2-5% of all cases of community-acquired pneumonia (CAP) requiring hospitalizations and it is the second most frequent cause of severe pneumonia requiring ICU admissions.

Legionnaire’s disease follows a socioeconomic gradient, with highest incidence occurring in the highest poverty areas.

MORTALITY/MORBILITY The mortality of community-acquired Legionnaire’s

disease ranges from 16 to 30% if untreated or treated with inactive antibiotic; the mortality for nosocomial LD can approach 50% given the underlying illness of the patient.

Progressive respiratory failure is the most common cause of death in patients with Legionella pneumonia.

The factors associated with high mortality rates include the following:

Age (older than 50 years old)Sex ( men > women)Predisposing underlying conditions, such as chronic lung disease, immunodeficiency, malignancies, end-stage renal disease, and diabetes mellitusNosocomial acquisitionDelayed initiation of specific antimicrobial therapy

ENVIRONMENTAL ECOLOGY &

TRANSMISSION Legionella has been isolated in natural aquatic

habitats (freshwater streams and lakes, water reservoirs) and artificial sources (cooling towers, potable water distribution systems).

Its optimal growth temperature is 28-40; organisms are dormant below 20 and are killed at temperaturas above 60

Transmission occurs by means of aerosolination or aspiration of water contaminated with Legionella organisms. The bacteria grow best in warm water, like the kind found in: hot tubes, cooling towers in air conditioning systems, potable water distribution systems (eg, showers, faucets), respiratory therapy equipment.

Most nosocomial infections and hospital outbreaks have been linked to contaminated hot water supply.

PATHOGENESIS OF INFECTION

CLINICAL MANIFESTATIONS Pneumonia is the predominant clinical manifestation of LD. After

an incubation period of 2-10 days, patients typically develop the following nonspecific symptoms:

Cough (Dry & Non-productive Productive)Shortness of breathHigh feverWeaknessMuscle achesHeadaches

PHYSICAL Fever is typically present. Temperatures

exceeding 40 occur in 20-60% of patients. Bradycardia may occur in patients with

advanced pneumonia. Hypotension has been reported in 17% of

patients with CAP. Lung examination reveals rales and

signs of consolidation late in the disease course.

GI symptoms: nausea, vomiting, diarrhea (watery) and abdominal pain.

Neurologic symptoms: altered mental status and encephalopathy.

The most common site of extrapulmonary infection in adults is the heart.

IMAGING STUDIES• The most common pattern is

patchy unilobar infiltrate that progresses to consolidation. Pleural effusions are also commonplace.

• In adults, cavitation is more common in patients who are immunocompromised.

LABS• Hematologic studies may reveal

leukocytosis and thrombopenia. • Erythrocyte sedimentation rate

(ESR) and C-reactive protein (CRP) levels are elevated.

• Chemistry studies may reveal elevated aminotransferase levels, hyponatremia, hypophospatema and creatine cinase levels.

• Urinalysis commonly reveals proteinuria and hematuria.

SPECIFIC LABORATORY FINDINGS Culture on selective media: SINGLE

MOST IMPORTANT TEST FOR LD.The standard media for Legionella isolation from contaminated clinical is buffered charcoal yeast extract agar (BCYE) supplemented with polymyxin, anisomycin, vancomycin, and dyes. Result: L pneumophila will appear apple-green. Urinary antigen testing: PREFERRED

INITIAL TEST FOR LD. It is rapid, relatively inexpensive, and practical for detection of L pneumophila. It has 70% sensitivity and approaches 100% specificity.

DIFFERENTIAL DIAGNOSIS

Aspiration/Bacterial/Viral pneumonia CAPs Respiratory distress

syndrome

Septic shock Meningitis

TREATMENT & PROGNOSIS Suspected or proven Legionella pneumonia should be treated in most patients with:Levofloxacin (quinolone) 750 mg once daily for 7-10 days.Azithromycin (macrolide) 1 gram on day one followed by 500 mg once daily for 7-10 days. Patients from long-term care facilities, those with nosocomial infections, and those who

have received transplant should be treated with a fluoroquinolone to provide better coverage of other gram negative bacilli, and, in case of transplant recipients, to avoid interaction between macrolides and immunosuppressive drugs.

It is recommended parenteral treatment initially for all patients with suspected Legionella pneumonia, given GI dysfunction in some patients.

The total duration of therapy for Legionella pneumonia is 7-10 days for azithromycin and quinolones. A longer course of quinolones of 21 days might be considered for immunosurpressed patients who are severely ill upon presentation.

With early initiation of appropriate therapy, most patients experience defervescence and symptomatic improvement with 3-5 days.

CLINICAL CLUES FOR LEGIONELLA DISEASE

DIAGNOSIS Presence of GI symptoms, especially diarrhea Neurologic findings, especially confusion Fever > 39 The gram stain of respiratory secretions shows

many neutrophils, but few, if any, microorganisms Hiponatremia (<130 meq/L) Hepatic disfunction Hematuria Failure to respond to beta-lactam and/or

aminoglycoside antibiotics.

PREVENTION Legionnaires’s disease is NOT

transmitted from person to person. Routine culturing of the hospital

drinking water should be performed regardless of whether or not cases of LD have been diagnosed.

Only sterile water should used to fill and rinse respiratory therapy devices.

If the water system is implicated, decontaminate the system by superheating water to 71-77 for 30 minutes.

REFERENCES1. Emedicine.medscape.com. Legionella Infection: Background, Pathophysiology,

Epidemiology [Internet]. 2015 [cited 27 July 2015]. Available from: http://emedicine.medscape.com/article/965492-overview

2. Uptodate.com. Treatment and prevention of Legionella infection [Internet]. 2015 [cited 27 July 2015]. Available from: http://www.uptodate.com/contents/treatment-and-prevention-of-legionella-infection

3. Prevention C. Legionella | Home | Pontiac Fever | Legionnaires Disease | CDC [Internet]. Cdc.gov. 2015 [cited 27 July 2015]. Available from: http://www.cdc.gov/legionella/index.html

4. Emedicine.medscape.com. Legionella Infection: Background, Pathophysiology, Epidemiology [Internet]. 2015 [cited 27 July 2015]. Available from: http://emedicine.medscape.com/article/965492-overview

5. Ppdictionary.com. Legionella pneumophila » Gram-Negative Bacteria » Pathogen Profile Dictionary [Internet]. 2015 [cited 27 July 2015]. Available from: http://www.ppdictionary.com/bacteria/gnbac/pneumophila.htm