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What are the symptoms of Mycobacterium marinum infection?

Typically, patients may initially notice a small red bump or non-healing red sore on their skin a few weeks after a history of exposure to non-chlorinated water. Ninety percent of the cases involve the arms (upper extremities). They may remember getting a scratch, scrape, or puncture wound several weeks before while in the water. Many people may easily overlook the early signs and try over-the-counter antibiotic creams and disinfectants on their own in an attempt to make the bump or sore go away. Often, patients may not decide to go to their physician until they can't get rid of the bump for weeks or months, when they see more bumps, or when they see spreading bumps in a "line" pattern up their arm or leg.

Some patients may feel no pain or itch while others commonly have some localized pain and firmness at the site of the infection. Most otherwise healthy people overall feel well during the infection and do not have fever or chills.

Patients in poor health or those with other health issues like an impaired immune system or other serious illnesses may experience fever, enlarged localized lymph nodes, and systemic infection.

When M. marinum infects the skin, it causes localized microscopic nodules to form. These nodules are called granulomas. They occur at sites of skin trauma where there are scratches, cuts, and the like.

The granulomas slowly increase in size usually become visible within two to three weeks of exposure. Some reported cases have developed two to four months or more after exposure to M. marinum because of the very slow-growing nature of this bacterium.

The most frequent sign is a slowly developing nodule (raised bump) at the site the bacteria entered the body. Frequently, the nodule is on the hand or upper arm. Later the nodule can become an enlarging sore (an ulcer). Swelling of nearby lymph nodes occurs. Multiple granulomas may form in a line along the lymphatic vessel that drains the site. These lesions will usually spontaneously heal in several months. This infection can also involve the joints (septic arthritis) and bones (osteomyelitis).

A health-care provider should be consulted if a skin nodule or reddened sore (ulcer) develops following direct skin contact with fresh or saltwater or after handling or processing fish.

For people with compromise of the immune system, M. marinum infection can be especially serious and involve disseminated (widespread) disease. If an infection is suspected under such circumstances, a health-care provider should be promptly consulted.

Return to Mycobacterium Marinum

See what others are saying

Comment from: Bill, 65-74 Male (Patient) Published: February 17

I was cleaning shrimp for the Christmas holidays last year. After the New Year, my finger swelled. Then my whole hand swelled up. I went to the doctor and he diagnosed it as gout and proceeded to give me steroid shots and a gout pack of medication to be taken for a week. Nothing got better. The pain was excruciating and I couldn't work with my hands at all, not even to feed myself. Finally, after coercing my physician, he took x-rays and blood work and told me to go to a hand surgeon. I did. My hand surgeon immediately put me in the surgical center and did a scraping. He diagnosed Mycobacterium marinum. I had to find an infectious disease doctor the next day. My infectious disease doctor gave me three weeks of IV therapy, and I am on clarithromycin, rifampin and ethambutol for 9 months now. My hand is better, but the medicines gave me bad side effects to my eyes.

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Comment from: Kathy, 55-64 Female (Patient) Published: November 11

I live on the gulf coast in northern Florida and have done a lot of fishing and kayaking where wading in the muck is unavoidable. I developed a small red painless bump on the inside of my ankle earlier this year, did not think much about it until it did not go away for a couple of months. I had it checked out by a dermatologist (in April) who said it looked ok, and should go away by itself. It was still there in the summer, and I had it checked out by my family doctor who also said it was nothing to worry about. By October, this small red bump had grown into a large red area and felt like there was fluid in it (looked like a boil). The ironic part of this is that I had the same thing happen about 15 years ago when I got the same type of infection in my finger after injuring it. At the time I had a fish tank and a water garden with Koi in it. I went back to the dermatologist and insisted that he check for Mycobacterium marinum infection. The biopsy came back positive. The first time I got it, I was antibiotics for almost a year. It looks like the same this time around.

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Comment from: Lucinda, 65-74 Female (Patient) Published: January 08

The tip of my first finger was swollen and a bit warm and red for over two months. When the swelling moved down my finger towards my hand, I consulted a doctor. It took 5 months to culture the a-typical mycobacterium to diagnose it as marinum. At its worst, half my hand and the finger were swollen, hot, itchy, and painful. I have been on a course of antibiotics for a month which has reduced the pain and swelling. With the specific diagnosis I expect that more targeted antibiotics, I will take for another 4 months, will cure the infection and I will have normal use of my hand. I swam every day in the summer in the Delaware Bay and frequently have scratches and cut on my hands. That is the most likely source of my infection.

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