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Legionella pneumophila Dr.T.V.Rao MD
History The bacterium got its name after a 1976 outbreak, when many people who went to a Philadelphia convention of the American Legion suffered from this disease, a type of pneumonia (lung infection). Although this type of bacterium was around before 1976, more illness from Legionnaires' disease is being detected now.
Disease Patterns Each year, between 8,000 and 18,000 people are hospitalized with Legionnaires' disease in the U.S. However, many infections are not diagnosed or reported, so this number may be higher. More illness is usually found in the summer and early fall, but it can happen any time of year.
Legionella pneumophila Legionella pneumophila is a thin, aerobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of legionellosis or Legionnaires' disease.
Legionella pneumophila Legionella pneumophila is a thin, aerobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of legionellosis or Legionnaires' disease
Morphology Thin, Non capsulated Gram negative bacilli 2 – 3 microns Coccobacillary Long forms in culture Motile with polar Bipolar flagella Staining with Silver impregnation methods
Culturing Grown on Buffered charcoal yeast extract agar with L cysteine with antibiotics When observed under microscope appear as cut glass L.pneumphila catalase +
Bacterial spread Legionella are present in stagnant water mud and hot springs Live also in free living ameba Human infection is typically by inhalation of aerosols provided by cooling towers and air conditioners Shower heads Out come of infection depends on size of infective dose
Spread of Infection
Transmission Legionella come from natural fresh water reservoirs, such as lakes, ponds, and puddles, where they parasitize on a broad range of protozoan species as hosts. The availability of the hosts plays a major role in the reproduction and mass release of highly infectious Legionella forms into environments where they can be spread by airborne water caplets and inhaled by people
Pathogenesis In humans, L. pneumophila invades and replicates in macrophages. The internalization of the bacteria can be enhanced by the presence of antibody and complement, but is not absolutely required. Internalization of the bacteria appears to occur through phagocytosis however L. pneumophila is also capable of infecting non-phagocytic cells through an unknown mechanism. Once internalized, the bacteria surround themselves in a membrane-bound vacuole that does not fuse with lysosomes that would otherwise degrade the bacteria. In this protected compartment, the bacteria multiply.
Who are at Risk Most healthy individuals do not become infected with Legionella bacteria after exposure. People at higher risk of getting sick are: Older people (usually 50 years of age or older) Current or former smokers Those with a chronic lung disease (like COPD or emphysema) Those with a weak immune system from diseases like cancer, diabetes, or kidney failure People who take drugs that suppress (weaken) the immune system (like after a transplant operation or chemotherapy)
Facts on Legionnaires Disease Legionella bacteria are not transmitted from person to person. People get Legionnaires' disease or Pontiac fever when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with Legionella bacteria. Keeping Legionella bacteria out of water is the key to preventing infection. Most people with Legionnaires' disease will have pneumonia (lung infection) since the Legionella bacteria grow and thrive in the lungs.
Pathogenesis Bacteria enter through alveoli Legionella multiply inside the Monocytes and Macrophages CMI effective
Predisposing factors Smoking Alcohol Age, Hospitalization Immunodeficiency status Can be Community acquired or Hospital acquired
Reservoirs of Infection L. pneumophila is a facultative intracellular bacterium that can invade and replicate inside amoebae in the environment, which can thus serve as a reservoir for L. pneumophila, as well as provide protection from environmental stresses, such as chlorination.
Clinically Manifest with Legionnaires Disease Epidemic Sporadic Incubation 2- 10 days Fever, non productive cough Dyspnea Pneumonia Diarrhea Encephalopathy Fatal if not treated in 15 – 20 % Respiratory failure
Pontiac fever Pontiac fever is a non-pneumonic form of L. pneumophila infection Symptoms are flu-like, including fever, tiredness, myalgia, headache, sore throat, nausea, and cough may or may not be present. Pontiac fever is self limited and requires no hospitalization or antibiotic therapies. There are no reported deaths associated with Pontiac fever.
Clinically Pontiac Fever manifests with A milder infection, also caused by Legionella bacteria, is called Pontiac fever. The symptoms of Pontiac fever are similar to those of Legionnaires’ disease and usually last for 2 to 5 days. Pontiac fever is different from Legionnaires' disease because the patient does not have pneumonia. Symptoms go away on their own without treatment.
Laboratory Diagnosis Specimens Sputum Bronchial aspirate Lung biopsy Florescent methods Serology ELISA
Diagnosis Most people with Legionnaires' disease will have pneumonia (lung infection) since the Legionella bacteria grow and thrive in the lungs. Pneumonia is confirmed either by chest x-ray or on physical exam.
Urine Antigen Test The most commonly used laboratory test for diagnosis is the urinary antigen test, which detects a part of the Legionella bacteria in urine (pee). If the patient has pneumonia and the test is positive, then the patient is considered to have Legionnaires' disease.
Culture If the Legionella bacteria are cultured (isolated and grown on special media) from sputum (phlegm), a lung biopsy specimen, or various other sites, the diagnosis of Legionnaires’ disease is also considered confirmed.
Blood SpecimensTesting the Serum Paired sera (blood specimens) that show a four-fold increase in antibody levels when drawn shortly after illness and several weeks following recovery, can also be used to confirm the diagnosis.
Pontiac Fever Pontiac fever can be confirmed by urine antigen or paired sera (blood specimens), but a negative test doesn’t rule out the diagnosis. It is often diagnosed clinically in the setting of other laboratory-confirmed legionellosis cases. Culture (isolating and growing the bacteria on special media) cannot be used to diagnose Pontiac fever.
Detection Sera have been used both for slide agglutination studies as well as for direct detection of bacteria in tissues using fluorescent-labelled antibody. Specific antibody in patients can be determined by the indirect fluorescent antibody test. ELISA and micro agglutination tests have also been successfully applied Legionella stains poorly with gram stain, stains positive with silver, and is cultured on charcoal yeast extract with iron and cysteine.
Treatment & ComplicationsTreatment Legionnaires' disease requires treatment with antibiotics (drugs that kill bacteria in the body), and most cases of Legionnaires’ disease can be treated successfully with antibiotics. Healthy people usually get better after being sick with Legionnaires’ disease, but hospitalization is often required. Pontiac fever goes away without specific treatment. Antibiotics provide no benefit for a patient with Pontiac fever.
Treatment Respiratory fluoroquinolones and the newer macrolides are used to treat L. pneumophila pneumonia. Treatment typically lasts 7-10 days or in the case of immunosuppressed patients, 21 days. Pontiac fever usually does not require antimicrobial therapy.
Treatment Macrolides Ciprofloxacin Tetracycline's Rifampicin
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