Legionella pneumophila

Legionella pneumophilaDr.T.V.Rao MD

HistoryThe 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 PatternsEach 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

MorphologyThin, 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 antibioticsWhen observed under microscope appear as cut glassL.pneumphila catalase +

Bacterial spreadLegionella are present in stagnant water mud and hot springsLive also in free living ameba Human infection is typically by inhalation of aerosols provided by cooling towers and air conditionersShower headsOut come of infection depends on size of infective dose

Spread of Infection

TransmissionLegionella 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

PathogenesisIn 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 RiskMost 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.

PathogenesisBacteria enter through alveoliLegionella multiply inside the Monocytes and MacrophagesCMI effective

Predisposing factors

SmokingAlcoholAge,HospitalizationImmunodeficiency statusCan 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

DiagnosisMost 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 TestThe 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.

CultureIf 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 FeverPontiac 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.

DetectionSera 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 appliedLegionella 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.

TreatmentRespiratory 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

MacrolidesCiprofloxacinTetracycline'sRifampicin

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