Legionella pneumophila pneumonia

Clinical History

The patient presented to the emergency room after 7 days of hyperpyrexia (maximum 39° C), productive cough, headache and right scapular pain. He had been under penicillin and cephalosporin treatment for 3 days, without any benefits.
Laboratory examinations showed high values of CRP (42.2 mg/dl) and WBC (14.000 mm3).

Imaging Findings

Chest radiograph showed a consolidation with air bronchogram in the right upper, middle and lower lobes and a right pleural effusion (Fig.1).
Sputum test results were negative for common germs and Koch's bacillus. A therapy based on rifampicin and ciprofloxacin was prescribed. After three days from the beginning of this therapy a contrast-enhanced CT was performed. CT scan revealed right unilateral involvement constituted by consolidation with air-bronchogram, mainly in the upper lobe (Fig.2), but also in the middle lobe, ground-glass opacities in the lower lobe (Fig.3), unilateral pleural effusion and some mediastinal lymphnodes (Fig.4).
Urinary test was positive for Legionella Pneumophila infection.

Discussion

Legionella microorganisms are responsible for sporadic and epidemic pneumonia, both community acquired and nosocomial. Since its first identification, in 1976, many species of Legionella have been discovered. Among them, mainly the group of Legionella Pneumophila can be related to human disease, and serogroup 1 causes more than 80% of human infections [1, 5]. This microorganism finds a natural habitat in water; human disease occurs when bacteria are inhaled. Legionella enters the cytoplasm of alveolar macrophages, inhibits its elimination and starts replication. Pneumonia is the most common clinical and often severe manifestation. However, Legionella can also cause Legionnaires’ disease, a pneumonia associated with gastro-intestinal, renal or central nervous system symptoms, or Pontiac fever, a self limiting flu-like illness [1, 2]. Diagnosis of Legionella Pneumophila infection is made with serological tests on sputum, blood and urine. Urinary antigen is cheap, easy to perform, and specific, though it identifies only serogroup 1. Legionella is successfully treated with macrolides or quinolones [1, 2]. There is not a specific radiological pattern; chest radiograph cannot distinguish Legionnaires' disease from other pneumonias [5]. Furthermore, imaging findings may vary on the basis of disease progression. At the beginning there is an opacification that gradually increases until it fills an entire lobe. If the infection persists, opacification will extend to other lobes including the contralateral lung [3]. Pleural effusion is quite common, and is seen in one third of cases [5]. Many studies have concluded that there is not a specific imaging pattern. However, imaging is crucial in establishing the presence of pneumonia and to evaluate its evolution [4].

Differential Diagnosis List

Final Diagnosis

Legionella pneumophila pneumonia

URL:	https://www.eurorad.org/case/10665
DOI:	10.1594/EURORAD/CASE.10665
ISSN:	1563-4086