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Infections Caused by Bacteria Related to Tuberculosis (TB)

(Nontuberculous Mycobacterial Infections)

By

Dylan Tierney

, MD, MPH , Harvard Medical School;


Edward A. Nardell

, MD, Harvard Medical School

Last full review/revision May 2018| Content last modified Jun 2018
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The bacteria that cause tuberculosis (TB) are classified as mycobacteria. Many types of mycobacteria exist. Many of the types that do not cause tuberculosis (called nontuberculous mycobacteria) can cause infections in certain people, sometimes with symptoms similar to those of tuberculosis. For example, if the lungs are infected, the main symptoms of tuberculosis and some nontuberculous infections are cough, fever, and weight loss.

The most common types belong to a group known as Mycobacterium avium complex (MAC), which includes Mycobacterium avium and Mycobacterium intracellulare.

Other nontuberculous mycobacteria that are not included in MAC also sometimes infect people.

Mycobacterium avium complex Infection

MAC mycobacteria usually cause infection only in the following people:

  • Frail older people

  • People with a weakened immune system

  • People with lungs that have been damaged by smoking for a long time, an old tuberculosis infection, bronchitis, emphysema, or other disorders

MAC lung infections

MAC infections of the lungs usually develop slowly. The first symptoms include coughing and spitting up mucus. People may feel tired, lose weight, and have a low-grade fever.

The infection may progress slowly or remain stable for long periods of time. If it progresses, people may regularly spit up blood and have trouble breathing.

Laboratory analysis of sputum taken from the infected person is needed to distinguish a MAC infection from tuberculosis. A chest x-ray is taken. It can show some differences between tuberculosis and a MAC infection.

Because drug resistance is often a problem when treating MAC infections, doctors tend to give infected people a combination of antibiotics. A combination of three drugs—clarithromycin or azithromycin, rifampin, and ethambutol—is often used. Drugs are usually taken for 12 to 18 months. If this combination is ineffective, other combinations are tried.

MAC lymph node infections

MAC infection of the lymph nodes may develop in children, typically those aged 1 to 5 years. The infection is usually caused by eating soil or drinking water that is contaminated with the mycobacteria.

Antibiotics are usually not necessary to cure the infection. Instead, the infected lymph nodes may be removed surgically.

Widespread MAC infections

A MAC infection can spread throughout the body in the following people:

  • People with AIDS

  • Rarely, people who have other disorders or take drugs that weaken the immune system

Symptoms include a fever, anemia, blood disorders, diarrhea, and abdominal pain.

To diagnosis widespread MAC infection, doctors usually try to grow (culture) the bacteria from a sample of blood or from tissue taken from the bone marrow, the liver, or an infected lymph node.

These infections are treated with two or three antibiotics, often clarithromycin or azithromycin plus ethambutol and sometimes rifabutin.

People with severe AIDS and a CD4 count of less than 100 need to take clarithromycin or azithromycin to prevent widespread MAC infection. Also, treating AIDS effectively is important. Such treatment can improve the immune system's ability to fight the infection.

Other Nontuberculous Mycobacteria Infections

Nontuberculous mycobacteria that are not included in MAC also sometimes infect people.

Skin infections

Some types of mycobacteria, usually Mycobacterium marinum, grow in swimming pools and even in home aquariums. These mycobacteria can cause skin infections when people swim in contaminated pools that have not been chlorinated, clean a contaminated home aquarium, or get a scrape or cut in their skin when they are handling contaminated fish or shellfish.

Reddish bumps may appear, enlarge, and turn purple. They usually occur on the arms or knees.

These skin infections may clear up without treatment if people have a normal immune system. However, infection can spread to other parts of the body if people have a weakened immune system.

People with chronic infections usually need treatment with minocycline, doxycycline, clarithromycin, or another antibiotic for 3 to 6 months.

Other infections

Worldwide, Mycobacterium ulcerans infection (also known as Buruli, Bairnsdale, or Daintree ulcer) is the third most common mycobacterial disease in people with a normal immune system, after leprosy and tuberculosis. Most infections occur in the tropical regions of West and Central Africa. In Australia, most cases occur in a temperate area around the city of Melbourne.

This infection starts as a lump under the skin, a large swollen area, or generalized swelling of the legs, arms, or face. The affected area is painless. The infection progresses, causing open sores on the legs or arms and resulting in widespread destruction of the skin and underlying tissues.

Mycobacterium ulceransinfection is treated with a combination of antibiotics and sometimes surgery.

Other types of mycobacteria, such as Mycobacterium fortuitum, can infect wounds, tattoos, and artificial body parts, such as a mechanical heart valve or a breast implant.

Another type of mycobacteria caused severe infections when contaminated water was used to clean out root canals in children.

Antibiotics and surgical removal of the infected areas and/or materials usually cure the infection. If this treatment is ineffective, people are referred to an experienced specialist.

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