Pulmonary Infection Due to Mycobacterium marinum in an Immunocompetent Patient

SIR—Mycobacterium marinum is a slow-growing and free-living mycobacterium that causes opportunistic infection in humans. This organism is widely distributed in aquatic environments [1], especially in relatively still or stagnant water. Infection is acquired by direct inoculation with the bacterium in an aquatic environment. It is a well-described cause of “swimming pool granuloma” or “fish tank granuloma” [2], which is manifested by cutaneous ulcer, nodules, or nodular lymphangitis, usually after the exposure of lacerations or abrasions to fresh water or salt water or after injuries associated with fish spines. To our knowledge, M. marinum has never been reported as a cause of pulmonary infection in humans in the English-language literature. The patient was a 51-year-old, previously healthy female homemaker who had 1 episode of cough with a small amount of hemosputum 5 days before hospital admission. The patient had no history of medical illness and had no risk factors for HIV infection. She did not recall receiving any insect bites, injuries, or wounds over the trunk or extremities. The patient denied a history of swimming, handling of fishes, or any exposure to a marine environment or animals in the 3 months before the onset of symptoms. The patient had no history of fever, chills, body weight loss, night sweats, dyspnea, chest pain, or use of an anticoagulant. Physical examination revealed that the breathing sound was clear, and no neck lymphadenopathy was found. The skin of 4 limbs was intact. The WBC count was 8200 cells/mm3 (52.8% neutrophils and 36.7% lymphocytes), and the carcinoembryonic antigen level was 0.65 ng/mL (normal value, <3 ng/mL). The results of cytologic testing, tuberculosis culture, and acid-fast staining of sputum samples were all negative. Bronchoscopy did not detect any bleeder or endobronchial lesion. Chest radiography revealed a nodular lesion with increased infiltration over the right lower lung field. Chest CT disclosed 1 indistinct nodular lesion in the right lower lobe, with pleural retraction and segmental atelectasis over the right lower lobe. No cavitation or calcification was seen. No thoracic adenopathies or abdominal abnormalities were found. Because of concern about possible malignancy, video-assisted thoracoscopic surgery was used to perform open lung biopsy. During the operation, right B6 segment atelectasis with an indurated lesion (size, ∼4 × ∼1.5 cm) was noted, and wedge resection of the right B6 segment was done. Pathologic examination revealed granulomatous inflammation with occasional Langhans' giant cell formation, but no organisms were identified by mycobacterial and fungal stain. Under the presumption of a diagnosis of tuberculosis, the patient was treated with isoniazid, rifampin, pyrazinamide, and ethambutol. The tissue biopsy specimen was ground and inoculated onto Lowenstein-Jensen media slants and cultured at 35°C in a CO2 incubator (5% CO2). After 20 days of incubation, the culture yielded a yellow-pigmented photochromogen, which was later identified as M. marinum by conventional biochemical methods.