Legionnaires’ Disease Questions

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What causes Legionnaire’s disease?

Legionnaire’s disease is caused by the bacteria Legionella pneumophila. The bacteria was first identified in 1977 by the CDC as the cause of an outbreak of pneumonia in Philadelphia. The disease caused by the bacteria is called legionellosis.

Who is at risk?

Legionnaire’s disease is an “opportunistic disease” in that it attacks the people who are the most vulnerable. These include persons who are elderly, smokers, diabetics and have had their immune systems suppressed.

How frequently does the disease occur?

Many cases of the disease go unreported because medical practitioners are not on the lookout for the disease. Only 1,000 cases per year are reported to the CDC, even though over 25,000 cases, causing more than 4,000 deaths, occur each year. Legionella is one of the top three causes of sporadic, community-acquired pneumonia (OSHA Technical Manual, Section III, Chapter 7, Legionnaire’s disease, page 2).

What are the symptoms of Legionnaire’s disease?

The disease has an incubation period of two to ten days with the harshest symptoms including coma and death, to the lesser symptoms of a mild cough and low fever. Malaise, muscle aches and slight headache typify the early symptoms, with high fever (up to 105 degrees), a dry cough, and shortness of breath seen in later symptoms. Vomiting, diarrhea, nausea and abdominal pain are also present frequently.

How is the disease diagnosed?

(A) Culture of the organism in the laboratory from viable cells of Legionella from sputum, bronchial washing or autopsy is the most reliable method of diagnosing the disease.

(B) Urine antigen test is a less reliable but strong indicator of the presence of Legionella pneumophila.

(C) Direct fluorescent antibody (DFA) staining of lung aspirates is less reliable because few organisms are present during the initial stages of the disease.

(D) An increase in the antibody level in the blood of an infected person occurs four to eight weeks after the onset of the disease. A fourfold increase in the antibody titer four to eight weeks after the initial blood test was performed, along with a positive diagnosis of pneumonia, is a very good indicator of Legionnaire’s disease.