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Swimming pool granuloma

Aquarium granuloma; Fish tank granuloma


A swimming pool granuloma is a long-term (chronic) skin infection. It is caused by the bacteria Mycobacterium marinum .



A swimming pool granuloma occurs when water containing Mycobacterium marinum bacteria enters a break in the skin. Signs of a skin infection appear about 2 to 3 weeks later.

Risks include exposure to swimming pools, salt water aquariums, or ocean fish.




The main symptom is a reddish bump ( papule ) that slowly grows into a purplish and painful nodule .

The elbows, fingers, and back of the hands are the most common body parts affected. The knees and legs are less commonly affected.

The nodules may break down and leave an open sore. Sometimes, they spread up the limb. Most often they stay a simple skin sore.


Exams and Tests


The health care provider will perform a physical examination and ask about your symptoms.

Tests to diagnose swimming pool granuloma include:

  • Skin test to check for tuberculosis infection, which may look similar
  • Skin biopsy and culture
  • X-ray or other imaging tests for infection that has spread to the joint or bone




Antibiotics are used to treat this infection. They are chosen based on the results of the culture and skin biopsy.

You may need several months of treatment with more than one antibiotic. Surgery may also be needed to remove dead tissue. This helps the wound heal.


Outlook (Prognosis)


Swimming pool granulomas can usually be cured with antibiotics. But, you may have scarring.


Possible Complications


Tendon, joint, or bone infections sometimes occur. The disease may be harder to treat in patients whose immune system is not working well.


When to Contact a Medical Professional


Call your health care provider if you develop reddish bumps on your skin that do not clear with home treatment.




Wash hands and arms thoroughly after cleaning aquariums. Or, wear rubber gloves when cleaning.




Vega-Lopez F. Mycobacterium marinum infection. In: Magill AJ, Hill DR, Solomon T, Ryan ET. Hunter's Tropical Medicine and Emerging Infectious Disease . 9th ed. Philadelphia, PA: Elsevier; 2013:chap 59.


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            Review Date: 2/3/2015

            Reviewed By: Amit M. Shelat, DO, FACP, Attending Neurologist and Assistant Professor of Clinical Neurology, SUNY Stony Brook, School of Medicine, Stony Brook, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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