In adults, Legionnaires' disease (LD) causes 2-15% of all cases of community-acquired pneumonia requiring hospitalization [1]. LD complicated by lung abscess was recently reported [2]. Extra-pulmonary legionella infection is rare and may involve the lymph nodes, brain, cranial nerves, kidney, liver, spleen, bone marrow, and heart [3] [4] ); with heart being the most common site. Few reports of pericarditis, myocarditis and endocarditis have been published [5], among these; myocarditis is the commonest [6].

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Figure 1. Electrocardiogram showing global ST segment elevation suggestive of acute pericarditis.

A 73-year-old man with a past history of diabetes mellitus presented to our hospital complaining of headache, fatigue and pleuritic type chest pain for 1 day. He denied any other symptoms. Vital signs were significant for temperature 37.4 °C, pulse 82/min, respiratory rate 20/min, blood pressure 140/58 mmHg and oxygen saturation 94% on room air. Electrocardiogram (ECG) showed global ST segment elevation suggestive of acute pericarditis. Laboratory investigations were significant for mild hyponatremia 134 meq/l with an elevated creatinine 1.4mg/dl. TTE showed pericardial effusion measuring 1.2 cm. Non-steroidal anti-inflammatory drugs were not given, because of concomitant renal failure, and the patient was started on colchicine. After 3 days he was discharged on colchicine following pain resolution.

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Figure 2. Chest X-ray showing enlarged heart's silhouette suggestive of pericardial effusion. Also, there is left pleural effusion with no evidence of lung infiltrates.

9 days later, he was readmitted to the hospital with low grade fever 37.8 °C, dry cough, diarrhea and similar chest pain. ECG showed persistent diffuse ST segment elevation (Figure 1). Laboratory investigations showed erythrocyte sedimentation rate (ESR) 140 mm/hr, C- reactive protein (CRP) 268 mg/dl, leukocyte count 11.9 × 10/mm³ and sodium 131 meq/l. Antinuclear antibodies, lupus anticoagulant and rheumatoid factor were negative. Chest X-ray showed enlarged heart's silhouette and pleural effusion without lung infiltrates (Figure 2). Detailed history revealed recent travel with an extended stay in a hotel room which involved direct contact to air condition. Repeat TTE denoted increased pericardial effusion to 3.2 cm without signs of tamponade and a newly found pleural effusion (Figure 3).

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Figure 3. Transthoracic echocardiography, parasternal long axis view, showing both pericardial effusion (3.25 cm) and pleural effusion (5.51 cm).

Legionella pneumophila (L. pneumophila) serogroup 1 antigen was detected by a strongly positive BinaxNOW urine legionella test. Levofloxacin was immediately initiated with rapid clinical improvement. Repeat BinaxNOW urinary legionella test after 20 hours of treatment with antibiotic was negative. After 3 days, repeated TTE showed decreased pleural effusion with decrease of pericardial effusion to 1.87 cm (Figure 4). Thoracentesis was done and pleural fluid culture failed to show any bacteria. Analysis of the fluid was negative for malignancy. Third and fourth BinaxNOW legionella tests after 6 and 20 days were also negative.

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Figure 4. Transthoracic echocardiography, parasternal long axis view, showing decreased pericardial effusion size to 1.87 cm.

Pneumonia is the predominant clinical manifestation of legionella infection. After an incubation period of 2-10 days; the disease starts as flu-like symptoms that progress to headache, lethargy, confusion and diarrhea [7]. Patients with heart involvement may present with chest pain, dyspnea and cough.

Recently; urinary legionella antigen tests have been increasingly used with significantly variable sensitivity and specificity. The BinaxNOW test has the highest sensitivity and specificity for L. pneumophila serogroup 1 antigen. Burke and Diederen et al. [8] [9] reported a specificity of 100% for the BinaxNOW test detecting L. pneumophila serogroup 1 antigen. The Centers for Disease Control (CDC) and Prevention recommend the urinary antigen for clinical laboratory use and confirmation of pulmonary or extra-pulmonary legionellosis with a specificity of 100% and a sensitivity of 70-100% [10]. Although the culture of the pleural fluid did not grow legionella, this may have been a false negative result for one of two reasons. First; the CDC reported a low sensitivity, 20-80%, of the fluid culture showing legionella bacterium [10]. This means that the culture can miss the diagnosis the time the fluid has the bacteria. Second; the pleural fluid culture was done after 3 days of antibiotic therapy, the time by which the BinaxNOW urine antigen was already negative, which may be secondary to eradication of the bacteria. The pericardial fluid culture would have strengthened the diagnosis; if positive. The risks of complications without a change in management or diagnosis already supported by CDC guidelines were deterrents to performing pericardial fluid culture. Also; there was a high chance that the pericardial fluid culture would be negative for the same reasons mentioned before. The rapid clinical, laboratory and radiological improvement after antibiotic therapy supported our diagnosis.

There is no clear data, identified in the medical literatures or by the manufacturer, regarding the time frame for which the BinaxNOW urine legionella test converts from positive to negative after initiation of antibiotic therapy.

A high level of suspicion and prompt early initiation of adequate antimicrobial therapy are critical to improve clinical outcomes in legionella infection. The recommended antimicrobial agents for L. pneumophila are quinolones, ketolides, and macrolides [11]. Certain fluoroquinolones (eg, levofloxacin, moxifloxacin) are effective and are recommended in severe disease as in heart involvement [12].

In conclusion, legionella pericarditis should be considered in the differential diagnosis of acute pericarditis. Early recognition and treatment are important to avoid more serious complications such as recurrent pericardial effusion, constrictive pericarditis [13] and cardiac tamponade [14]. Urinary antigen testing is now an established and valuable tool for the diagnosis of LD, particularly in regions where L. pneumophila serogroup 1 is the most common cause of the disease. To our knowledge; this is the first reported case to show rapid conversion of the BinaxNOW urine legionella test from positive to negative within 24 hours of antibiotic therapy.

- All authors declare no conflict of interest.

- All authors had access to the data and participated in preparing this manuscript.

- All of the named authors have agreed to the submitted draft of the paper.