Abstract: 【Abstract】 Objective To investigate clinicopathological features of swimming pool granuloma. Methods From January 2018 to January 2021, 56 patients with swimming pool granuloma were collected from Tianjin Academy of Traditional Chinese Medicine Affiliated Hospital, and their clinical and pathological characteristics were retrospectively analyzed. Results Among the 56 patients, 16 were males and 40 were females, with an average age of 60.84 years. The most common exposure type among these patients was handling of infected fishes or seafood by aquaculture workers and residents in daily cooking （31/56）, with the average incubation period being 4.58 weeks and average time to diagnosis being 3.19 months. All skin lesions were located at the upper extremities, mainly manifesting as erythema and papular nodules, and sometimes as pustules, ulcers, granulomas or verrucous plaques. Eleven patients presented with solitary skin lesions, 36 with sporotrichoid skin lesions, and 6 with bilateral sporotrichoid lesions. Histopathologically, infectious granulomas were observed in all patients except 4 without specific changes, and 37 presented with characteristic exudative necrosis, with varying amounts of fibrinoid exudative or necrotic elements in the center, and a large number of neutrophils, histiocytes and multinucleated giant cells infiltrating or surrounding it. Sequences of Mycobacterium marinum were identified in all 56 cases by metagenomic DNA sequencing of pathogenic microorganisms. Conclusion In Tianjin area, swimming pool granulomas mostly affects elderly females, handling of infected fishes or seafood is the main type of exposure, and skin lesions are histopathologically characterized by exudative necrotic granulomas.

Key words: Granuloma, Marine mycobacterium, Skin manifestations, Pathologic processes, Metagenome, Swimming pool granuloma