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Swimming Pool Granuloma

Last updated Sept. 27, 2020

Approved by: Maulik P. Purohit MD, MPH

Swimming Pool Granuloma is a rare, chronic skin infection caused by the bacterium Mycobacterium marinum.

What are the other Names for this Condition? (Also known as/Synonyms)

  • Aquarium Granuloma
  • Fish Bowl Granuloma
  • Fish Tank Granuloma

What is Swimming Pool Granuloma? (Definition/Background i\Information)

  • Swimming Pool Granuloma is a rare and chronic skin infection caused by the bacterium Mycobacterium marinum. The condition was initially described (during early 1950s) to develop following an exposure to swimming pool waters
  • With the development of appropriate water treatment systems (such as chlorination), the incidence of Mycobacterium marinum infection from a swimming pool source has almost been eliminated
  • Nevertheless, a chronic exposure to untreated swimming pools, salt water aquariums, and contact with marine animals (lake, river, or ocean) tend to increase the risk of occurrence of this infection
  • A Swimming Pool Granuloma develops when water containing this bacterium enters the body through a cut or injury in the skin. It is initially characterized by the appearance of small reddish raised areas on skin, which goes on to involve deeper tissues if left undetected
  • The elbows, fingers, and back of the hands are the most commonly affected areas. The symptoms start appearing after 2-3 weeks of exposure to the bacteria. Immunocompromised individuals may present severe symptoms and complications
  • Swimming Pool Granuloma can be cured through the administration of antimycobacterial therapy. The prognosis is excellent with early and appropriate treatment

Who gets Swimming Pool Granuloma? (Age and Sex Distribution)

  • Any individual (child or adult) who is exposed to Mycobacterium marinum bacterium is at risk for Swimming Pool Granuloma
  • It affects both genders (men and women) equally
  • No racial, ethnic, or geographical predominance is observed
  • Swimming Pool Granuloma is a very rare infection; the estimated incidence stands at 0.27 cases per 100,000 individuals

What are the Risk Factors for Swimming Pool Granuloma? (Predisposing Factors)

Risk factors that tend to increase the incidence of Swimming Pool Granuloma due to Mycobacterium marinum include:

  • Regular swimmers and instructors are at risk from exposure to swimming pools that are inadequately chlorinated. It is important to note that cases of infections are not reported from swimming pools that are adequately sanitized and treated 
  • Exposure to natural waterbodies such as lakes and ponds
  • Working or being exposed to saltwater or freshwater aquariums
  • Exposure to marine animals (both ocean and river), such as fish, shellfish, turtle
  • Handling, cleaning, processing, or packaging fish
  • Fishing as a hobby may also cause an infection risk
  • Deep-sea and shallow-sea diving
  • Any exposure to contaminated water
  • Individuals with poor immune system

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Swimming Pool Granuloma? (Etiology)

Swimming Pool Granuloma is an uncommon bacterial infection affecting the skin caused by Mycobacterium marinum.

  • This opportunistic pathogen infects the body through (open) skin cut wounds resulting in the condition. Infection spread from one individual to another is very rare, except in case of immunocompromised individuals (who are highly vulnerable to the infection)
  • Mycobacterium marinum is found in both salt water and fresh water (any aquatic) environment

What are the Signs and Symptoms of Swimming Pool Granuloma?

On exposure to the bacteria, it takes about 3 weeks for the signs and symptoms to develop. Swimming Pool Granuloma signs and symptoms due to Mycobacterium marinum include:

  • Appearance of reddish bumps on the skin
  • The lesions develop into painful nodules and turn purple in color
  • The lesions or nodules break and present themselves as open sores on the skin

How is Swimming Pool Granuloma Diagnosed?

A diagnosis of Swimming Pool Granuloma may involve:

  • Complete evaluation of medical (including occupational and recreational) history along with a thorough physical exam
  • Skin test to rule-out tuberculous infection
  • Tissue biopsy of the affected region: A small sample of tissue is taken and sent to the laboratory for examination under the microscope by a pathologist, and also to check for the presence of bacteria
  • Tissue culture of the affected region for culture studies: It is important to inform the testing lab, the possibility of a tuberculous marinum infection, since special culture methods are needed to detect growth of M. marinum bacterium
  • Polymerase chain reaction (PCR) test: A molecular test for individuals with active infection that is performed on blood samples, to detect M. marinum
  • TB screening QuantiFERON test may show a false positive result for M. marinum
  • Enzyme linked immunospot (ELISpot) assay may also show a false positive result for M. marinum
  • X-ray and imaging tests, such as MRI scans, when infection has spread to the joints and bones

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Swimming Pool Granuloma?

Swimming Pool Granuloma due to Mycobacterium marinum may lead to the following complications:

  • Draining sinuses on the skin with presence of fluid and pus
  • Tenosynovitis: It is an inflammation of the sheath that covers the tendons, resulting in pain and swelling in the affected areas. A tendon is a cord that joins muscles to the bones
  • Septic arthritis: Pain and swelling of the joints caused by the bacteria
  • Osteomyelitis: Bone infection caused by bacteria

How is Swimming Pool Granuloma Treated?

  • Antimycobacterial therapy is the standard treatment for Swimming Pool Granuloma due to Mycobacterium marinum
  • In rare cases, surgery may be required

The type of antibiotics used is usually dependent upon the culture study results. Some of the commonly used antibiotics include:

  • Doxycycline
  • Minocycline
  • Clarithromycin
  • Rifampin
  • Trimethoprim-sulfamethoxazole

How can Swimming Pool Granuloma be Prevented?

Preventive measures that may be adopted for decreasing the incidence of Swimming Pool Granuloma include:

  • Individuals working or dealing with aquatic or marine animals should thoroughly wash and clean (their entire body) themselves after their work
  • Adequate treatment of swimming pools (such as proper chlorination), aquariums, and water rides in theme parks
  • Wearing rubber gloves while cleaning is also helpful

What is the Prognosis of Swimming Pool Granuloma? (Outcomes/Resolutions)

  • The prognosis for Swimming Pool Granuloma is generally excellent with proper treatment
  • The affected individuals can be cured easily with the help of antibiotic therapy
  • However, individuals with suppressed immune systems are at increased risk for severe forms of the infection

Additional and Relevant Useful Information for Swimming Pool Granuloma:

Please visit our Infectious Diseases Health Center for more physician-approved health information:


What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

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Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: May 26, 2015
Last updated: Sept. 27, 2020