Mycobacterial Infections, Atypical

Atypical mycobacterial (my-ko-bak-TEER-e-ul) infections are infections caused by mycobacteria ^* other than those that cause tuberculosis ^*

What Are Atypical Mycobacterial Infections?

Atypical mycobacteria are commonly found in the environment, like in soil and water, and in food. Most of the time they do not cause infection or illness in healthy people. When a person's immune system is weakened, however, as in people who have HIV or AIDS, several strains of mycobacteria can cause opportunistic infections ^* . Atypical mycobacteria are related to the bacterium that causes tuberculosis (TB), but they often are resistant to the drugs used to treat TB. These strains are called mycobacteria other than tuberculosis, or MOTT.

Although some mycobacteria can live on human skin or in the nose, atypical mycobacterial infections are not known to spread from person to person. Rather, infection comes from direct contact with the bacteria in the environment.

Are Atypical Mycobacterial Infections Common?

Mycobacterial infections other than tuberculosis are uncommon, and they most frequently affect people with HIV or AIDS. As cases of HIV and AIDS have increased, so have cases of mycobacterium infections. In the United States, these infections are more common than tuberculosis. People with seriously weakened immune systems or chronic lung disease are at greatest risk.

How Do People Know They Have an Atypical Mycobacterial Infection?

Signs and symptoms of atypical mycobacterial infections include fever, swollen lymph nodes, extreme tiredness, night sweats, weight loss, diarrhea (dye-uh-REE-uh), joint and bone pain, cough, shortness of breath, skin lesions ^* , general discomfort, and paleness. Many of these symptoms can be signs of less serious conditions, but in a person with a weakened immune system a combination of such symptoms suggests a MOT T infection. In children, lymphadenitis ^* is the most common type of MOT T infection, whereas lung infections, which occur less often in children, are the most common in adults.

Exposure to Mycobacterium marinum can lead to a rare infection known as swimming pool granuloma" or "aquarium granuloma." About 3 weeks after the bacteria enters through a break in the skin, usually on the hands, reddish bumps appear. This infection can be prevented by avoiding contact with contaminated water and wearing gloves or washing thoroughly when cleaning aquariums.

Custom Medical Stock Photo, Inc.

What Are Some Specific Infections?

Mycobacterium avium complex (MAC)

MAC includes the species Mycobacterium avium (A-vee-um) and Mycobacterium intracellulare (in-truh-sel-yoo-LAR-e) and most commonly causes lymphadenitis and lung disease in otherwise healthy people. Patients who have AIDS are particularly susceptible to MAC, and it often spreads to the blood, lungs, spleen, liver, bone marrow ^* , and intestines in people with HIV. MAC infection in an HIV-positive person can signal the start of full-blown AIDS. Disseminated disease ^* rarely occurs in people with healthy immune systems.

Mycobacterium marinum

This infection causes skin lesions, sometimes known as swimming pool granuloma ^* or fish tank granuloma. Infection with M. marinum (MAR-ih-num) is very rare, occurring in less than 1 in 100,000 people. Those who are most at risk include people with weakened immune systems and people who handle fish, are exposed to contaminated water in aquariums, or swim in fresh or salt water that contains the mycobacterium. Several weeks after a person has contact with contaminated water, a bump appears on a hand, arm, or foot where there was a break in the skin. The lesion grows and drains over several weeks, leaving an ulcer ^* . Occasionally, a deep infection will cause tenderness and swelling in the nearby bone or joints.

Mycobacterium ulcerans

Mycobacterium ulcerans (UL-sir-ans) is found in tropical and subtropical regions in Asia, the Western Pacific, and Latin America, although it is most common in West Africa. The infection causes skin lesions known as Buruli (boo-REH-lee) ulcers, named for a region in Uganda in Africa. The ulcers develop mainly on the limbs, grow slowly, and release a toxin (or poison) that damages the skin and underlying tissue. The infection is relatively painless, but if left untreated it can destroy massive amounts of skin and bone, leading to permanent deformities.

Mycobacterium kansasii

Infection with Mycobacterium kansasii (kan-ZAS-e-eye) causes a lung disease similar to tuberculosis, although not as severe. Patients may experience fever and cough, and a doctor often hears wheezing and "crackling" when listening to the patient's lungs. It also can involve the lymph nodes and cause skin lesions. In people with weak immune systems, the infection can erupt into widespread disease. This infection is rare in the United States, but people with chronic lung disease are especially susceptible. If left untreated, the disease frequently worsens and can be fatal.

How Do Doctors Diagnose and Treat Atypical Mycobacterial Infections?

A doctor can perform several tests to detect mycobacteria, including examination and culture ^* of samples of blood, sputum ^* , bowel movement, or bone marrow. Chest X rays or computerized tomography ^* (CT) scans can show disease in the lungs. Some cases may require endoscopy ^* to collect a sample of lung or stomach tissue or biopsies ^* of skin or lymph node tissue. Quickly diagnosing mycobacterial infections is crucial, as treatment needs to begin as soon as possible.

The PPD (purified protein derivative) skin test for tuberculosis will often be positive, although not as strongly so, in people who have an atypical mycobacterial infection, because atypical mycobacteria are so similar to the bacterium that causes TB.

Treatment for mycobacterial infections depends on the type of bacterium, the location and severity of the infection, and the status of the person's immune system. Resistant and severe infections usually need to be treated with a combination of antibiotics, and up to six medications may be used at once. Surgery, sometimes along with medications, is the most effective way to treat lymph node infections and skin lesions.

Treatment for MOTT infections can take as long as 6 months to 2 years. Antibiotics work during the growth stage of bacteria, and mycobacteria are slow growing. If left untreated, MOTT infections can spread throughout the body, especially in people with weak immune systems. They can cause abscesses ^* , bone and joint infections, and infections of the lymph nodes, lungs, or soft tissue. Widespread infections can lead to serious illness and even death.

Can People Prevent Atypical Mycobacterial Infections?

Because mycobacteria are common in the environment, these infections are difficult to prevent, especially in people with weakened immune systems. Preventive medications are prescribed for people at risk, such as those with HIV or AIDS. Getting enough sleep and eating a healthy diet also can help these patients cope with and fight these infections.