Legionellosis, or Legionnaire's disease, is a severe and sometimes fatal disease caused by species within the Legionella genus of bacteria. It can be inhaled from contaminated water supplies and has become a major cause of nosocomial pneumonia. About 8000 to 12,000 people in the United States are affected every year by either Legionnaire's or the less potent Pontiac fever.
The bacteria thrives in stagnant water and can often be found in air-conditioning cooling towers or other places where still, warm water is common. Most individuals who develop the disease are exposed to contaminated water droplets in the air rather than the disease being passed from person to person.
Legionnaire's disease has the same symptoms as other pneumonias, which include fever, cough, fatigue, anorexia, headache, myalgia and even diarrhea. The average incubation time is between two and ten days. Pontiac fever, which is caused by L. pneumophila, requires no treatment.
Legionellosis is diagnosed by the growing of culture on special media and then silver staining. The bacteria can also be found in the sputum or its antigen in urine.
The drug of choice for treatment is erythromycin, an antibiotic with a range close to or wider than penicillin that is used for people with penicillin allergies. Other drugs used for treatment include rifampin, macrolides such as azithromycin and fluoroquinolones.
Respiratory status and vital signs should be monitored very carefully. In severe cases, the levels of consciousness must be evaluated at intervals for signs of neurological deterioration and seizure precautions should be instituted as needed. There may be the use of respiratory care including oxygen therapy, and the respiratory therapist may need to assist in intubation and ventilation of the patient. Fluid and electrolyte balance should be monitored and replacement therapy used as needed.
Like many other respiratory diseases, older patients are far more likely to suffer severe symptoms and to die from the disease. Legionellosis often strikes most heavily in facilities where the elderly are common and rarely leave the building, such as nursing homes.