legionnaires disease

A severe lung infection by Legionella pneumophila which may occur sporadically or in an epidemic with a mortality of up to 15%; depending on the population, Legionella spp cause 1­­–27% of community-acquired pneumonias; male:female ratio, 3:1
Epidemiology Most L pneumophila infections are associated with water supplies and ventilation systems; most epidemics occur during the summer with 0.5–5% attack rates; the only documented mode of spead is aerosol
Sources Plumbing, shower heads, water-storage tanks, evaporative condensors, cooling towers
Risk factors Cigarettes, alcohol, renal transplant, elderly
DiffDx Sporadic LD mimics myoplasma pneumonia, Q fever, tularemia, plague, psittacosis, influenza and other viral pneumonias
Lab Decreased Na+, decreased PO4-, increased liver enzymes, proteinuria, microscopic hematuria, relative leukocytosis, increased ESR, hyponatremia, increased ALT, increased AST, increased BR, azotemia
Complications Empyema, shock, DIC, renal failure, neurologic sequelae, peripheral neuropathy
Management Erythromycin, T-S, penicillin
Prognosis 15–20% mortality w/o therapy; up to 50% of immunocompromised patients die
Poor prognostic features Tachycardia, tachypnea, WBCs 14,000/mm3, increased BUN, increased creatinine, hyponatremia, hypoxia, leukopenia, bilateral infiltrates on chest films
Prevention Chlorination of water supply for showers and ventilation systems; UV irradiation of water supplies

legionnaires’ disease

a rare human pneumonial condition, caused by the bacterium Legionella pneumophila, that can lead to death. The disease was named after an outbreak occurring at an American Legion convention in a Philadelphia hotel in 1976, the bacteria eventually being traced to the air-conditioning plant of the hotel. Since then a number of cases have been reported in connection with recirculated hot water systems such as cooling towers. There is no evidence of person-to-person transmission.