Definition of Legionnaires Disease

Legionnaires’ disease is a serious and potentially fatal form of pneumonia first identified in 1976 when several hundred people attending a Legionnaires’ convention became ill, a number of whom died as a result of the infection.

Scientists subsequently isolated the causative bacterium Legionella pneumophila. The bacteria infect about 18,000 people in the United States each year, about 4,000 of whom die from the disease or its complications. A less severe form of the infection with the same bacteria is Pontiac fever, which presents milder forms of similar symptoms (though without subsequent complications).

Health experts refer to these infections collectively as legionellosis. Heating and cooling systems in buildings can harbor L. pneumophila, which then spread the bacteria through ventilation networks. Frequent and diligent cleaning of these systems is the most effective means for limiting outbreaks of infection.

Symptoms and Diagnostic Path

Legionnaires’ disease begins as a typical viral upper-respiratory infection with symptoms that begin 3 to 10 days after exposure and include fever, generalized aches and discomfort, loss of appetite, headache, fatigue, and cough. Some people also have gastrointestinal symptoms such as diarrhea.

Within a week the symptoms worsen to include coughing up sputum, chest tightness or pain, and dyspnea (shortness of breath). Some people also experience multiple neurologic symptoms, including confusion and cognitive dysfunction.

A chest X-RAY shows signs of pneumonia, and diagnostic blood tests often show indications of infection in the body. The doctor may order specialized tests to detect the presence of L. pneumophila in the sputum or of L. pneumophila antigens in the urine.

A key factor in suspecting Legionnaires’ disease is knowing the possibility of exposure, either because others have become ill or because the person was at an event at a setting conducive to transmitting Legionnaires’ disease, such as a large convention. Other water sources as well as respiratory equipment in hospitals harbor L. pneumophila, which has become a common cause of communityacquired pneumonia as well as of nosocomial infections (hospital-acquired infections).

Treatment Options and Outlook

The primary treatment for Legionnaires’ disease is hospitalization for intravenous therapy with the antibiotic medications of the macloide or fluoroquinoline class (such as azithromycin or levofloxacin). Illness in some people is mild enough to allow outpatient treatment with oral antibiotics, though others may require hospitalization. As with any severe infection, multiple system failure is a significant risk in people who already have other major health conditions such as cardiovascular disease (cvd), diabetes, or pulmonary disorders.

Early diagnosis and treatment are critical; the likelihood of death resulting from the infection increases dramatically when people delay seeking medical care or doctors are unaware of the possibility of the diagnosis. Among people who are otherwise healthy, have normal immune function, and receive prompt treatment, more than 95 percent recover. However, many people continue to have some symptoms, such as fatigue, for several months.

Risk Factors and Preventive Measures

Infection with L. penumophila can occur in several venues. People who already have some form of pulmonary compromise, such as asthma or chronic obstructive pulmonary disease (copd), seem more likely to contract Legionnaires’ disease than people who have healthy lung function with equal exposure to a contaminated source. People who smoke have the highest risk, whether or not they have underlying pulmonary disease. People between the ages of 50 and 70 seem most likely to develop infection after exposure.

The most effective preventive measure is strict maintenance and cleaning of building air-conditioning and heating systems, spas, whirlpools, and other potential sources of culture for the bacteria. Heightened awareness about Legionnaires’ disease has resulted in improved diligence.

The US Occupational Safety and Health Agency (OSHA) has implemented guidelines for building maintenance. Because the bacteria enter the upper respiratory tract during breathing, there are few personal measures to reduce the risk for infection as often it is not possible or practical to avoid locations that are potential sources of infection.


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