Legionnaires' Disease & Pontiac Fever

Legionnaires' disease and Pontiac fever are diseases of the respiratory system. (Read about "Respiratory System") They are the result of an infection of legionella bacteria. (Read about "Microorganisms")

Legionellosis, which is the term used to describe diseases caused by the legionella bacteria, has two distinct forms:

• Legionnaires' disease - This is the more severe form of infection which includes pneumonia. (Read about "Pneumonia")
• Pontiac fever - This is a milder illness, causing flu-like symptoms without pneumonia.

The National Institute of Environmental Health Sciences (NIEHS) says the first known outbreak of Legionnaires' disease in the U.S. occurred in 1976. It was first thought that the bacteria had been growing in the air-conditioning unit of a hotel in Philadelphia where the Pennsylvania state American Legion held a convention. New evidence suggests that the bacteria was in the hotel water supply also, not just the air conditioners, according to the Centers for Disease Control and Prevention (CDC). About 180 people were infected and 29 deaths occurred. This event is where the disease, and the bacteria that cause it, got their names.

CDC says an estimated 8,000 to 18,000 people get Legionnaires' disease in the United States each year. Some people can be infected with the legionella bacterium and have mild symptoms or no illness at all. Legionnaires' disease can attack anyone, but people middle aged or older have a greater risk of getting it.

Outbreaks of Legionnaires' disease often receive significant media attention. However, this disease usually occurs as single isolated cases not associated with any recognized outbreak. When outbreaks do occur, they are usually in the summer and early fall, but cases may occur year-round. Between 5 - 30 percent of people who get Legionnaires' disease die.

Legionella organisms can be found in many types of water systems. However, the bacteria reproduce the most in warm, stagnant water (90-105 degrees F), such as that found in certain plumbing systems and hot water tanks, cooling towers and evaporative condensers of large air-conditioning systems and whirlpool spas, according to NIEHS.

The original theory, according to the Environmental Protection Agency, was that the legionella bacteria are spread when a person inhales a mist of some type that contains the bacteria. What often happens is water pipes can develop a plaque from deposits in the water. In this plaque, the bacteria find a home that is warm and moist. This is the ideal condition for the bacteria. The bacteria then can sometimes get knocked loose into the water. When a person is taking a hot shower, the bacteria are now floating in the water vapor all around them. The bacteria are inhaled into the lungs where they begin an infection. Another theory, which is gaining some currency, is that it is contracted through aspiration. This is when a person chokes on something in a way that saliva is unable to enter the esophagus but instead enters the trachea and flows into the lungs. So if someone drinks water contaminated with legionella bacteria and then chokes, they can spread it to their lungs in that manner.

CDC emphasizes that legionella is not spread person to person. It is not spread from animals to humans. (Read about "Animal & Insect Borne Diseases") The elderly, cigarette smokers, people with chronic lung or immunocompromising disease, such as AIDS, and people receiving immunosuppressive drugs are all more susceptible to the infection. (Read about "Quit Smoking" "Chronic Obstructive Pulmonary Disease" "HIV / AIDS") Pontiac fever most commonly occurs in people who are otherwise healthy.

Symptoms

Common symptoms of Legionnaires' disease are fever, chills and a cough, which can be dry or produce mucus. Some other symptoms are muscle aches, headache, tiredness, loss of appetite and sometimes diarrhea. (Read about "Diarrhea") Chest x-rays (Read about "X-rays") often show pneumonia. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone; other tests are required for diagnosis. When looking at a chest x-ray, Legionnaires' disease looks no different from any other types of pneumonia, and is hard to tell from just the symptoms alone. Special tests are most often needed, according to CDC.

Persons with Pontiac fever experience fever and muscle aches and do not have pneumonia. They generally recover in 2 to 5 days without treatment.

The time between the patient's exposure to the bacterium and the onset of illness for Legionnaires' disease is 2 to 10 days; for Pontiac fever, it is shorter, generally a few hours to 2 days.

Antibiotics (Read about "Antibiotics") are the most useful method of dealing with Legionnaires' disease. CDC says erythromycin is the most common. In some cases, rifampin may be used along with erythromycin. Pontiac fever is usually just allowed to run its course.

Related Information:

    Glossary of Respiratory Terms