Legionnaires' Disease and Pontiac Fever (Legionellosis)

  • Medical Author:
    George Schiffman, MD, FCCP

    Dr. Schiffman received his B.S. degree with High Honors in biology from Hobart College in 1976. He then moved to Chicago where he studied biochemistry at the University of Illinois, Chicago Circle. He attended Rush Medical College where he received his M.D. degree in 1982 and was elected to the Alpha Omega Alpha Medical Honor Society. He completed his Internal Medicine internship and residency at the University of California, Irvine.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What is the treatment for Legionnaires' disease?

There are three major classes of antibiotics that are effective in treating legionellosis. These include the fluoroquinolones such as levofloxacin (Levaquin), and moxifloxacin (Avelox), the macrolides such as erythromycin, azithromyocin (Zithromax), and clarithromycin (Biaxin), and the tetracyclines including doxycycline (Vibramycin). A new class of antibiotics (glycylcyclines) are also effective. The choice of antibiotic is often dependent on the patient's clinical state, tolerance to the medication, and degree of certainty as to the diagnosis. Zithromax and Levaquin are particularly effective because of decreased gastrointestinal irritation, higher potency, better penetration into tissue, and once-daily dosing.

In severe cases of Legionnaires' disease that seem more resistant to a single antibiotic, a second drug called rifampin (Rifadin) may be added.

Pontiac fever requires no specific treatment.

How is Legionnaires' disease spread?

Outbreaks of legionellosis have occurred after people have inhaled aerosols that come from a water source (for example, air-conditioning cooling towers, whirlpool spas, or showers) contaminated with Legionella bacteria. People may be exposed to these aerosols in homes, workplaces, hospitals, or public places. Infection cannot be acquired from another person with legionellosis, and there is no evidence of people becoming infected from vehicle air conditioners or household window air-conditioning units.

Cases of Legionnaires' disease have increased throughout the United States, but this most likely represents increased detection by better diagnostic tests. Some would suggest that this increase may be due to global warming, though this seems unlikely.

Hospital-acquired infections have occurred and are usually due to contamination of the water supply. Two well-reported cases occurred in the 1980s in Los Angeles, one at the Wadsworth VA hospital and the other at the City of Hope. Guidelines have now been established for routine environmental testing for Legionnaires' in several states in the United States and by the Veterans Affairs health-care system.

With regard to travel-associated infection, this usually occurs in hotels from contaminated water, most notably at the Legionnaires' convention in Philadelphia. This disease has also been associated with travel on cruise ships.

Some data suggest an increase incidence of Legionnaires' in the elderly in nursing homes linked to eating puréed food, probably also due to increased aspiration in this population.

Medically Reviewed by a Doctor on 3/23/2016
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