The organism. The family Legionellaceae comprises more than 49 species with more than 64 serogroups. The species L. pneumophila causes 80
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1. Legionella Pneumonia By Dr.Sujith S
2. The organism The family Legionellaceae comprises more than 49 species with more than 64 serogroups.
The species L. pneumophila causes 80–90% of human infections and includes at least 16 serogroups; serogroups 1, 4, and 6 are most commonly implicated in human infections.
To date, 18 species other than L. pneumophila have been associated with human infections, among which L. micdadei (Pittsburgh pneumonia agent), L. bozemanii, L. dumoffii, and L. longbeachae are the most common.
3. Members of the Legionellaceae are aerobic gram-negative bacilli- do not grow on routine microbiologic media.
Buffered charcoal yeast extract (BCYE) agar is the medium used to grow Legionella.
Antibiotics added to the medium suppress the growth of competing flora from nonsterile sites, and dyes color the colonies and assist in identification
4. The direct fluorescent antibody (DFA) test can identify a number of individual species.
In the case of L. pneumophila, the serogroup-specific antigen and antibodies detected by immunofluorescence are directed primarily at the lipopolysaccharide, a prominent outer-membrane component
5. Ecology &Transmission L. pneumophila - aquatic bodies, including lakes and streams.
The organisms can live for years in refrigerated water samples.
Factors known to enhance colonization by and amplification of legionellae include warm temperatures (25°–42°C), stagnation, and scale and sediment
6. L. pneumophila form microcolonies within biofilms.
Its eradication from water-distribution systems requires disinfectants that can penetrate the biofilm.
The presence of symbiotic microorganisms, including algae, amebas, ciliated protozoa, and other water-dwelling bacteria, promotes the growth of L. pneumophila.
Legionellae can invade and multiply within free-living protozoa
7. The source of Legionella is water.
Community-acquired Legionnaires' disease has been linked to colonization of residential and industrial water supplies.
Potable-water distribution systems in hospitals, long-term-care facilities, hotels, and large buildings have been implicated.
Sporadic community-acquired cases have been linked to residential water systems
8. Multiple modes of transmission of Legionella to humans exist
Direct instillation into the lungs during respiratory tract manipulations.
Aspiration is now known to be the predominant mode of transmission
9. Pathogenesis Legionella enters the lungs through aspiration or direct inhalation.
Attachment to host cells is mediated by bacterial type IV pili, heat-shock proteins, and the major outer-membrane protein.
10. Legionella binds to complement CR1 and CR3 integrin receptors on the surface of the host cell.
The organisms possess pili that adhere to respiratory tract epithelial cells.
Conditions that impair mucociliary clearance, including cigarette smoking, lung disease, or alcoholism, predispose to Legionnaires' disease
11. Cell-mediated immunity - primary mechanism of host defense against Legionella.
12. Alveolar macrophages readily phagocytose Legionella.
The attachment of the bacteria to phagocytes is mediated via Fc receptors and complement receptors, which attach to the bacterial major outer-membrane protein.
Binding to these receptors promotes phagocytosis but fails to trigger an oxidative burst.
13. The L. pneumophila phagosome resists acidification and evades fusion with late endocytic compartments and lysosomes.
The humoral immune system is active against Legionella. Type-specific IgM and IgG antibodies are measurable within weeks of infection.
Immunized animals develop a specific antibody response, with subsequent resistance to Legionella challenge. However, antibodies neither enhance lysis by complement nor inhibit intracellular multiplication within phagocytes
14. Pontiac Fever Pontiac fever is an acute, self-limiting, flu-like illness with an incubation period of 24–48 h.
Malaise, fatigue, and myalgias are the most common symptoms, occurring in 97% of cases.
Fever (usually with chills) develops in 80–90% of cases and headache in 80%.
Other symptoms (seen in <50% of cases) include arthralgias, nausea, cough, abdominal pain, and diarrhea.
Modest leukocytosis with a neutrophilic predominance is sometimes detected.
15. Legionnaires' Disease (Pneumonia) The incubation period for Legionnaires' disease is usually 2–10 days.
Nonspecific symptoms—malaise, fatigue, anorexia, and headache—are seen early in the illness.
The mild cough of Legionnaires' disease is only slightly productive.
The sputum is rarely,streaked with blood.
Chest pain—either pleuritic or nonpleuritic—can be a prominent feature and, when coupled with hemoptysis, can lead to an incorrect diagnosis of pulmonary embolism.
16. Fever? Temperatures in excess of 40.5°C (104.9°F) were recorded in 20% of the cases
Relative bradycardia has been overemphasized as a useful diagnostic finding; it occurs primarily in older patients with severe pneumonia.
Chest examination reveals rales early in the course and evidence of consolidations as the disease progresses.
Abdominal examination may reveal generalized or local tenderness.
17. Clinical manifestations that occurred significantly more often in Legionnaires' disease :
Diarrhea, neurologic findings (including confusion), and a temperature of >39°C.
Elevated values in liver function tests
Hematuria also occurred more frequently in Legionnaires' disease.
Other laboratory abnormalities include creatine phosphokinase elevation, hypophosphatemia, serum creatinine elevation, and proteinuria
18. Gastrointestinal difficulties are often pronounced; abdominal pain, nausea, and vomiting affect 10–20% of patients.
Diarrhea (watery rather than bloody) is reported in 25–50% of cases.
The most common neurologic abnormalities are confusion or changes in mental status.
Headache, lethargy to encephalopathy.
19. Clinical Clues Suggestive of Legionnaires' Disease Diarrhea
High fever (>40°C; >104°F)
Numerous neutrophils but no organisms revealed by Gram's staining of respiratory secretions
Hyponatremia (serum sodium level <131 mg/dL)
Failure to respond to -lactam drugs (penicillins or cephalosporins) and aminoglycoside antibiotics
Occurrence of illness in an environment in which the potable water supply is known to be contaminated with Legionella
Onset of symptoms within 10 days after discharge from the hospital
20. Since the portal of entry for Legionella is the lung in virtually all cases, extrapulmonary manifestations result from bloodborne dissemination from the lung.
Isolation of the organism from sputum, Legionella was isolated from the blood by a special culture method in 38% of cases