Outbreak of a cutaneous Mycobacterium marinum infection in Jiangsu Haian, China

Mycobacterium marinum is a slow-growing mycobacterium. In November 2008, we diagnosed a patient with M. marinum infection who worked at a fish farm in Jiangsu Haian, China. We conducted an investigation and found 18 patients with the same infection. In suspected cases, complete data were collected including medical history, clinical manifestations, laboratory features, and responses to treatment. Therapeutic regimens, including clarithromycin monotherapy or combined treatment with clarithromycin, rifampicin, and ethambutol, were prescribed. A total of 18 patients with M. marinum infection were found. All patients showed only skin lesions. Biopsies were performed and 16 patients showed infective granulomas. Acid-fast bacilli stain (Ziehl-Neelson stain) for cutaneous samples were positive in 7 patients. Ten patients were positive in purified protein derivative tests (tubercles were ≥10 mm in diameter). In 16 patients, colonies grew after tissue samples were incubated on Löwenstein-Jensen medium at 32 °C. All the isolates were identified as M. marinum by polymerase chain reaction-restriction fragment length polymorphism analysis, by direct gene sequencing, and by genotyping using mycobacterial interspersed repetitive units. Fifteen of the 18 patients were cured using clarithromycin-containing antibiotic regimens. The history of contact with fish and aquaria plays an important role in diagnosis. Clarithromycin-containing regimens were successful in most patients with M. marinum infections limited to the skin.