Pleural empyema with gas formation caused by mixed infection of Edwardsiella tarda with Streptococcus constellatus.

Edwardsiella tarda is an anaerobic, gram-negative rod bacterium associated with freshwater and marine life. Human E. tarda infections are rare, and most infections in humans cause gastroenteritis. Extraintestinal infections of E. tarda such as pleural empyema are particularly rare. A 72-year-old man was admitted with cough and purulent sputum. His medical history included periodontal disease and gastric cancer for which he had undergone total gastrectomy. Chest computed tomography showed left pleural effusion with foci of gas, and both E. tarda and Streptococcus constellatus were cultured from the pleural effusion. Thus, he was diagnosed with gas-forming empyema. He was successfully treated with therapeutic thoracentesis and antibiotics. Our case suggests that a dietary habit of raw fish, undernutrition, gastrectomy and oral infection may be predisposing factors for empyema caused by E. tarda.