LEGIONELLOSIS (Leigonnaires'disease, pontiac Fever)

This newly-recognized entity is caused by a Gram negative organism, Legionella pneumophilia, which is recovered from central air-conditioning systems, stream water, mud, etc. It infects through inhalation.
Predisposing factor include:

• Cancer or other disorder of immunosuppression
• Steroid therapy
• Renal homograft
• Diabetes mellitus therapy using diuretics

Legionnaires' disease is a multisystem disorder with a relatively longer incubation period ( 2 to 10 days). Manifestations include high fever, chills, cough, chest pain (pneumonia is the hallmark of the condition), myalgia, headache, confusion and diarrhea. In addition, liver and kidney dysfunction, convulsions, erythema nodosum, acute cerebellar ataxia, meningitis, etc. may occur.
Pontiac fever has a short incubation period (24 to 48 hours) and ,manifests with influenza-like illness minus pneumonia.
Diagnosis of legionellosis is by isolating the causative bacillus, or by serologic tests showing elevated antibody titer.
Whereas pontiac fever needs only symptomatic/supportive therapy, specific treatment is strongly indicated in case of legionnaires' disease. This consists in administering intravenous erythromycin, 40mg/kg/day, every 6 hourly. In the event of a poor response, a combination of erythromycin and rifampicin is the choice. Tetracyclines, contrimoxazole, and ciprofloxacin are also effective.
Supportive therapy includes supplemental oxygen, assisted ventilation, correction of dyselectrolytemia, and management of renal failure and shock with vasoactive drugs.
Prevention is directed at removal of the impliciated source, say in a cooling tower or an evaporative condensor, as also respiratory isolation of the patient.