IS Case 194: Legionella pneumonia

Lisa Siripun, MD


Imaging Sciences URMC 2008
Publication Date: 2009-05-22

History

A 43-year-old male presented with cough and night sweats for 2 weeks.

Findings

Patchy opacity of the right lower lobe.

Diagnosis

Legionella pneumonia

Discussion

Legionellosis causes 2-15% of all cases of community-acquired pneumonia (CAP) requiring hospitalization and is the second most frequent cause of severe pneumonia requiring ICU admission. Predisposing underlying conditions are chronic lung disease, immunodeficiency, malignancies, endstage renal disease, and diabetes mellitus. Middle-aged and older adults have higher risk of developing Legionnaires' disease (LD) than do young adults and children. Transmission occurs by means of aerosolization or aspiration of water contaminated with Legionella organisms. After an incubation period of 2-10 days, patients typically develop the following nonspecific symptoms such as fever, weakness and fatigue. Respiratory symptoms may not be present initially but develop as the disease progresses. Almost all patients develop a cough, which is initially dry and nonproductive, but may become productive, and chest pain.

Pneumonia is the predominant clinical syndrome of LD. Chest radiographic findings of LD are variable, nonspecific, and indistinguishable from those observed with other pneumonias. Although initial chest radiographs may be normal, especially in patients with nosocomial disease, the usual progression of findings on serial studies is from patchy areas or nodular appearance to multilobar, almost homogeneous, infiltrates. Unilateral involvement is more common than bilateral involvement. Purely interstitial infiltrates are rare. Pleural effusion, present in at least one-third of patients, may be the only abnormality. In adults, cavitation is more common in patients who are immunocompromised, but it has been described in children who were immunocompetent. Radiographic findings usually progress despite appropriate antibiotic therapy; infiltrates may take as long as 4 months to resolve completely.

References

  1. Rathore MH, Alvarez A. Legionella infection. eMedicine. August 8, 2007. http://emedicine.medscape.com/article/965492-overview
  2. Amanullah S, Posner DH, Farhad M, Lessnau K-D. Pneumonia, atypical bacterial. eMedicine. March 7, 2008. http://emedicine.medscape.com/article/363083-overview

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