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December 2004, Volume 34 Number 12 , p 24 - 24





  • Assessing signs and symptoms

  • How to treat and prevent disease



    IN THE SUMMER OF 1976, an outbreak of pneumonia at an American Legion convention in Philadelphia, Pa., was traced to contaminated water in the convention hotel's air conditioning system. About 180 people became ill and 29 died. The responsible pathogen, a Gram-negative bacterium, was isolated and named Legionella pneumophila . The most severe form of the infection it causes, Legionnaires' disease, is characterized by pneumonia. Legionella also causes Pontiac fever, a less severe illness characterized by fever and muscle aches, but not pneumonia. Most people recover without treatment.

    Currently, 18 groups of L. pneumophila and 35 related Legionella species have been recognized, but L. pneumophila serogroup 1 is the type most often associated with disease. It can reproduce in high numbers only in a narrow temperature zone—from 90° F to 105° F (32° C to 41° C)—so it thrives in warm, stagnant water found in certain plumbing systems, hot water tanks, and spas.

    Legionella is transmitted when someone inhales aerosolized water vapor from the air around contaminated water. Disease ( legionellosis ) develops when a susceptible person inhales enough bacteria from a contaminated source, such as a shower, a bedside humidifier, or aerosolizing respiratory therapy equipment.

    The percentage of people who become ill after exposure is low: 0.1% to 5%. Those most susceptible to disease include the elderly, cigarette smokers, people with chronic lung or other disease, and those who are immunocompromised.

    According to the Centers for Disease Control and Prevention, 23% of Legionnaires' disease cases are nosocomial. The infection doesn't spread person to person, so isolation isn't necessary.

    Assessing ...

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