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Nasty Infectious Diseases You Want To Avoid - Legionnaires' Disease

Updated on December 31, 2008

This is a bacterial infection that can take one of two distinct forms: Legionnaires' disease or Pontiac fever. Legionnaires' disease is the more severe form of infection, which includes pneumonia; Pontiac fever is a milder illness.

An estimated 10,000 to 15,000 people are diagnosed with Legionnaire's disease each year; an additional unknown number are infected with the Legionella bacterium but rarely have any symptoms. Cases have been identified throughout the United States and in several foreign countries and is believed to occur worldwide.

Outbreaks usually occur in the summer and early fall, but cases may occur yearround. Between 5 and 15 percent of known cases of Legionnaires' disease have been fatal.

People of any age may contract the disease, but it usually affects middle-aged or older people (especially those with chronic lung disease and smokers). Anyone with an impaired immune system or who takes drugs that impair the immune system are at higher risk. Pontiac fever, on the other hand, commonly occurs in healthy individuals and resembles a flu like illness rather than pneumonia.

The disease was named for its first identied outbreak, which occurred in 1976 during a Legionnaire convention at the Bellevue-Stratford Hotel in Philadelphia; 182 Legionnaires became ill and 29 died. Most of them had pneumonia, and because doctors didn't know what the men had, they called it "legionnaire's disease." In January 1977, scientists identified the bacterium that causes the disease and realized it had also caused outbreaks before 1976; nevertheless, the name remained.

Cause - Legionnaires' disease (and a separate variety called Pontiac fever) is caused by the bacterium Legionella pneumophila transmitted by breathing in bacteria carried in water droplets through the air. The bacteria live in water and get into air-conditioning cooling towers and circulate throughout a building. Outbreaks have occurred after persons have inhaled spray from a contaminated bacteria. water source (such as air-conditioning cooling towers, whirlpool spas, or showers) in workplaces, hospitals, or other public places. Infection isn't spread from one person to another, and there is no evidence of people becoming infected from auto air conditioners or household window air conditioners. Legionella can be found in many different water systems, but the bacteria reproduce best in warm, stagnant water such as is found in some plumbing systems and hot water tanks, cooling towers and condensers of large air conditioning systems, and whirlpool spas.

Symptoms - Between 2 and 10 days after exposure, symptoms of fever, chills, and cough appear. The cough may be dry or produce sputum; some patients may also experience muscle aches, headache, fatigue, loss of appetite, and diarrhea. Symptoms in Pontiac fever usually appear within a few hours to two days.

Diagnosis - It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone. Other tests are needed for diagnosis. Lab tests may show decreased kidney function; chest X-rays reveal pneumonia. A diagnosis requires special tests not normally performed on suspected cases of pneumonia: looking for bacteria in sputum, finding antigens in urine, and comparing antibody levels in two blood samples three to six weeks apart. Experienced doctors are the most important diagnostic tool, since lab tests take several days to months.

Treatment - Erythromycin is the recommended antibiotic for Legionnaires' disease; sometimes, rifampin may be used in severe cases. Pontiac fever does not require medication.

Prevention - Outbreaks must be reported to the health department. The disease can be prevented by better design and maintenance of cooling towers and plumbing systems in order to limit the growth and spread of bacteria.


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