Mycobacterium marinum as a rare cause of soft tissue infections of the upper extremity: A multidisciplinary multicenter approach to symptoms, diagnosis and treatment

Background: Infections with Mycobacteriummarinum (M. Marinum) are rare but clinically significant and difficult to diagnose skin and soft tissue infections, typically occurring after contact with contaminated water. The hand is most frequently affected, particularly in individuals with regular exposure to aquariums, leading to the term “fish tank finger”. This study explores the pathogenesis, epidemiology, clinical manifestations, diagnosis, and treatment of M. Marinum infections of the hand and presents a case series of seven patients from Eastern Saxony, including a region-specific antibiotic susceptibility analysis. Materials and methods: This retrospective multicenter study examines all seven cases of M. Marinum infections of the extremities between 2019 and 2024. We conducted an analysis of available antibiograms to identify regional characteristics of M. Marinum infections and establish a standardized treatment approach for patients in Eastern Germany. Results: In this study, seven M. Marinum infections were documented between 2019 and 2024. The average patient age was 65.5 years, with five male and two female patients. Infections primarily affected the hand (71.4%), with the average wound size being 2.84 cm². The mean time to diagnosis was 3.64 months. Notably, 57.1% of patients reported aquarium ownership, and two cases were linked to water exposure abroad. All patients received a three-month dual antibiotic therapy, with clarithromycin and either rifampicin or ethambutol. No recurrences were observed. Antibiotic susceptibility testing showed uniform minimal inhibitory concentration (MIC) values for rifampicin, clarithromycin, and rifabutin. Surgical debridements were performed in two cases in total. Conclusion: Upper limb infections caused by M. Marinum are an important differential diagnosis in cases of persistent skin lesions following water exposure. Early diagnosis and targeted therapy are essential to prevent complications. For infections in Eastern Germany, we recommend a radical surgical debridement combined with adjunctive antibiotic therapy consisting of Clarithromycin (500 mg twice daily) along with either rifampicin (600 mg daily) or rifabutin (150 mg twice daily) for a minimum duration of three months.