Legionnaires’ disease refers to pneumonia cause by the Legionella species. It was first recognized in 1976 when an outbreak of pneumonia took place at a hotel in Philadelphia during the American Legion Convention. Legionella pneumophila is a bacterium that was isolated from lung specimens from the victims at autopsy. The source of these bacteria is water. It has been isolated in lakes, streams, cooling towers and potable water supply sources. It can survive in refrigerated water samples for years. However once the organism enters the human constructed reservoirs, tanks etc. it grows and multiplies by leaps and bounds. It grows favourably at warm temperatures and in stagnated waters.
Transmission of the organism: There are many ways the organism can be transmitted to humans for example by aerosolization, aspiration and direct instillation into the lungs. However it is unclear whether Legionella enters the lungs via oropharyngeal colonization or directly via the drinking of contaminated water.
Incidence: The incidence of Legionnaires’ disease depends on the degree of contamination of the aquatic reservoir, the immune status of the persons exposed to the infection and the intensity of exposure. Risk factors for suffering from this disease are cigarette smoking, immunocompromised status, chronic lung disease, old age. Hospital acquired pneumonia or community acquired disease may occur and may not bear the typical risk factors mentioned.
Clinical features: Incubation period is 2 to 10 days. Patients present with mild cough which is usually slightly productive, in some cases the sputum may be streaked with blood. Other symptoms are mild fever, headache, malaise, lethargy, anorexia, myalgia and arthralgia. Some patients present with shortness of breath. Gastrointestinal manifestations like diarroea, nausea, vomiting and abdominal pain may be seen. Various neurological abnormalities too may be seen like headache, lethargy or even encephalopathy. On examination the patient is febrile, relative bradycardia may be seen, abdominal tenderness may be generalized or localized. Chest examination reveals rales in the early course of disease and progresses to consolidation.
Diagnosis of Legionnaires’ disease: chest radiographs show pulmonary infiltrates, pleural effusion, consolidation. Nodular opacities seen may show cavitations and quick spread in immunosuppressed cases. In such cases, pulmonary abscesses too may be seen.
Sputum samples obtained by bronchoalveolar lavage or otherwise must be sent for gram staining and culture. In cases of pleural effusion, pleural tapping may be done and DFA staining, culture must be done.
The assay for Legionella soluble antigen in the urine is a rapid and relatively inexpensive test to be performed and is highly specific.
Antibody testing of both acute and convalescent phase sera is necessary. A fourfold rise in the titer is diagnostic of infection.
Treatment: Antibiotics are used for the treatment of Legionella infection. Macrolides like Azithromycin, Clarithromycin, Quinolones like Levofloxacin, Ciprofloxacin, Ofloxacin, Tetracyclines like Doxycycline, Tetracyclines, Minocycline etc.
Prevention: Routine environmental culture of the hospital water supply is recommended as an approach to the prevention of hospital acquired Legionnaires’ disease. Disinfection of the water supply also is effective. Legionella bacteria can be inactivated by UV light.
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