Aquarium granuloma
Aquarium granuloma (also known as fish tank granuloma and swimming pool granuloma) is a rare skin condition caused by a non-tubercular mycobacterium known as "Mycobacterium marinum". Skin infections with "M. marinum" in humans are relatively uncommon, and are usually acquired from contact with contaminated swimming pools, aquariums or infected fish. Signs and symptoms. Aquarium granuloma presents as a slow-growing, inflamed red bump (nodule or plaque) at the site of infection. It is characterized by a painful, itchy skin lesion,  and may become ulcerated or crusted. Skin changes usually appear roughly three weeks after the aquatic exposure . If this condition is acquired from an aquarium, then often the dominant hand is affected. If this condition is acquired from a swimming pool, then symptoms can also develop on trauma-prone body zones, such as the elbows, knees, feet and tip of the nose. Cause. For the infection to develop in humans, the two main factors required are exposure to contaminated water, and abrasion or injury to the skin. Hence, this infection is commonly seen in individuals who clean fish tanks, handle ornamental fish and work in wet fields. Aquatic systems with a high density of fish and warm  waters appear to be conditions particularly favorable to this infectious agent, and increase the changes to contract fish tank granuloma. Poor water quality and various nutritional deficiencies are also possible contributing factors. Swimming pool granuloma can occur when there is inadequate chlorination of swimming pools. Diagnosis. Aquarium granuloma is relatively nonspecific in clinical presentation. Therefore, more common skin conditions, like cellulitis, foreign body reaction, skin cancer, and fungal or parasitic infections, are often explored first. Overall, diagnosis and treatment of this rare skin infection is often delayed because of a lack of suspicion. Lab tests for finding "M. marinum" include  cultures where a swab or sample is taken and grown in the laboratory. Cultures of "M. marinum" are fairly difficult to grow, and results may take several weeks. The culture may be negative, even if there is an active infection. Treatment may still be considered even if the test results are negative, especially if the patient's history supports past fish or fish-tank exposure.  In the absence of positive culture results, a skin or tissue biopsy may be a helpful test to render a microscopic diagnosis. Another technique that can be used to detect the bacteria is Polymerase Chain  Reaction (PCR). A biopsy sample itself is sufficient to detect the exact type of bacteria by means of PCR. Treatment. Treatment involves the use of antibiotics. Since M. marinum has a high tendency for multi-drug resistance, treatment by one particular drug will not be effective. Often, up to six different antimicrobial regimes may be needed before the infection responds to a particular drug combination. This combination of antibiotics is based on the results of the culture and skin biopsy. The treatment can take up to several months. Surgery may also be needed to remove dead tissue if the lesions  do not clear with antibiotics. This helps the wound to heal. Epidemiology. "Mycobacterium" "marinum" infection is not contagious; it is not spreading from person to person. It is also not transmitted in hospitals like other common bacteria.