Legionella pneumophila causes both community acquired infections and hospital acquired infections in immunocompromised patients.

This genus has named after a famous outbreak of pneumonia occurred among the people who attended to the American Legion convention in Philadelphia in 1976.

It was named as Legionnaires’ disease. This occurred due to the spreading of bacteria in aerosols. These aerosols could travel 1-2 Km.

These infected aerosols generated from different water sources such as, ponds in cooling towers, hot water systems in hotels, homes and hospitals.

Warm water in oxygen line humidifiers and nebulizers, spa baths and showers.

This organism mainly causes Legionnaires’ disease. It is a type of pneumonia condition. It may progress rapidly when it is not treated with appropriate antibiotics.

If it is untreated, mortality rate is high. Other than that L. pneumophila causes Pontiac fever.

It is a type of influenza-like febrile illness. This disease does not cause death. In addition, Legionellae cause infections such as prosthetic valve endocarditis and wounds infection.

The natural habitat of Legionellae is environmental water sources such as air conditioners and water-cooling towers. Legionella pneumophila can be subdivided into three subspecies.

They are Legionella pneumophila ssp. pneumophila, Legionella pneumophila ssp. fraseri and Legionella pneumophila ssp. pascullei. Usually person to person transmission is not occurred.


Gram staining of sputum is done. They are weakly gram negative. They stain very poorly by Gram stain.

However, in Gram stained smears many neutrophils can be seen.

In smears prepared directly by clinical samples, Legionellae can be seen as short rods or coccobacilli. But smears prepared by cultures, they become large and filamentous. They can be stained by silver impregnation method.


Sputum, bronchial aspirate or washings, pleural fluid, lung biopsy or autopsy material are used for culture.

pneumophila are pleomorphic, aerobic and flagellated organisms. They are non- spore-forming organisms. They grow better in 2.5–5% carbon dioxide at 35–36°C.

pneumophila fails to grow in normal culture media. They grow on special media namely buffered charcoal yeast-extract agar (BCYE).

It is a special type of medium with iron and cysteine. Colonies occur after 48 h to 5 days of incubation.

Colonies are grey-white in color and show “cut glass” appearance under the plate microscope.

Under ultraviolet light, they can be seen as fluorescing blue–white.

Moreover, these organisms cultured on cysteine-deficient medium to demonstrate that they do not grow on cysteine-deficient media.

Cultures are identified by immunofluorescence test by specific antisera.

For the typing of these organisms, molecular methods such as gene sequencing are also used.

Indirect immunofluorescence assay is useful for the diagnosis of L. pneumophila.

It diagnosed by measuring the antibody titre in convalescent-phase serum.

If there is any significant increase in antibody titre (a four-fold or greater rise in antibody titre or a single titre of 256 or more), diagnosis can be done.

There is a rapid diagnostic test for the diagnosis of L. pneumophila antigens in urine.

It is an enzyme-linked immunosorbent assay (ELISA).

Furthermore, demonstration of Legionella antigen in infected lung tissue is done by fluorescent-antibody staining. PCR test is also available for rapid diagnosis of the disease.

Moreover, L. pneumophila is urease negative, non-fermentative, oxidase positive, catalase positive.

However, above mentioned molecular and serological tests are widely used for the identification of the organism than biochemical tests.


Mainly azithromycin or any other macrolide is given intravenously for the treatment of legionella pneumonia.

In severe disease, Fluoroquinolone (ciprofloxacin) or rifampicin is used for the treatment.

β-lactam antibiotics and Aminoglycoside are not effective against this infection.

Prevention and Control

There is no vaccine for this infection. Eradication of Legionella from water sources should be done for the control of the disease.

Aerosol production should be eliminated from the Water sources.

Eradication of Legionella from water sources can be done by heat, disinfection of water by using chlorine or other biocides.

In addition, copper-silver ionization is another method for the eradication of Legionella from water sources.

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