Legionnaires’ Disease - Emerging Infectious Disease

LEGIONNAIRES’ DISEASE

Legionnaires’ disease is a multisystem illness that usually includes pneumonia and is caused by the gram-negative bacteria, Legionellapneumophila. Named after an outbreak of the disease amongpeople attending a convention of the American Legion in 1976, its potential to cause outbreaks has been demonstrated numerous times in hospitals and other settings. Legionella organisms are found in many man-made and naturally occurring water sources. Although the organisms may initially be introduced in low num-bers, growth is enhanced by water storage, scaling (biofilm) on the inside of water towers, temperatures ranging from 25° to 42°C (77° to 107°F), and certain amoebae frequently present in water that can support intracellular growth of legionellae.

Pathophysiology

L. pneumophila is transmitted by an aerosolized route from anenvironmental source to an individual’s respiratory tract. It is not transmitted from person to person. In hospitals, patients may be exposed to aerosols created by cooling towers, water sources from plumbing, and respiratory therapy equipment. Because under-lying medical conditions can increase host susceptibility and sub-sequent severity of disease and because hospital plumbing systems are often very complex, outbreaks occur in hospitals more fre-quently than at other centers within the community. Mortality rates among hospitalized patients are about twofold greater than those for people with community-acquired Legionella pneumonia (CDC, 2002e).

Risk Factors

Risk factors strongly associated with Legionella infection include diseases that lead to severe immunosuppression, such as acquired immunodeficiency syndrome (AIDS), hematologic malignancy, end-stage renal disease, or use of immunosuppressive agents. Other factors associated with increased risk include advanced age, diabetes, alcohol abuse, smoking, and other pulmonary disease

Clinical Manifestations

The lungs are the principal organs of infection; however, disease without pulmonary involvement has been reported. Other organs may also be involved. The incubation period ranges from 2 to 10 days. Early symptoms may include malaise, myalgias, head-ache, and dry cough. With disease progression, the patient develops increased pulmonary symptoms, including productive cough, dyspnea, and chest pain. Patients are usually febrile, and body temperatures may reach 103°F (39.4°C) and higher. Diar-rhea and other gastrointestinal complaints commonly accompany the array of pulmonary symptoms. In severe cases, multiorgan involvement and failure may follow.

Assessment and Diagnostic Findings

Laboratory tests available for the diagnosis of Legionella include culture (ie, using special microbiologic methods and media), im-munofluorescent microscopy, antibody titer interpretation, and urinary antigen detection. Diagnosis of Legionella by antibody titer requires evidence that titers have increased at least fourfold over time. A single elevated titer is not sufficient to determine current disease. The urinary antigen test (for L. pneumophila serotype 1, the most prevalent subspecies) is helpful because urine is easy to obtain and the test remains positive after initial anti-biotic treatment. This persistent marker especially aids in the diagnosis of community-acquired pneumonia as patients are fre-quently treated empirically. Legionella cultures rapidly become negative after antibiotic treatment, even when the patient’s con-dition is deteriorating. Frequently, more than one laboratory test is used in the diagnosis of Legionella because no one test is 100% sensitive. The diagnostic approach generally involves accumu-lation of information obtained from the history, physical exam-ination, x-rays, laboratory findings, and assessment of therapeutic effectiveness. Chest x-ray abnormalities may vary in severity and in location of the diseased site.

Medical Management

Azithromycin (Zithromax) is considered the antibiotic of choice. Other options include clarithromycin (Biaxin), erythromycin (Ilotycin), and levofloxacin (Levaquin).

Nursing Management

The nursing management described for the patient with any pneumonia should form the basis of care for the patient with Legionella pneumonia. Special isolation techniques are not used for these patients because there is no evidence of transmission between humans.