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Infections That Resemble Tuberculosis (TB)

(Other Mycobacterial Infections)

By Dylan Tierney, MD, MPH , Instructor; Associate Physician, Division of Global Health Equity, Harvard Medical School; Brigham and Women's Hospital
Edward A. Nardell, MD, Professor of Medicine and Global Health and Social Medicine; Associate Physician, Divisions of Global Health Equity and Pulmonary and Critical Care Medicine, Harvard Medical School; Brigham & Women's Hospital

Many types of mycobacteria (a group of bacteria that includes tuberculosis bacteria) exist. Many of them can cause infections with symptoms similar to those of tuberculosis.

The most common types belong to a group known as Mycobacterium avium complex (MAC). Although these mycobacteria are common, they 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

Similar to tuberculosis, a MAC infection affects primarily the lungs but may also affect the lymph nodes, bones, skin, and other tissues. Unlike tuberculosis, a MAC infection cannot be passed from one person to another.

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.

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.

Widespread infections

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

  • People with AIDS

  • Rarely, people with other disorders that weaken the immune system

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

To diagnosis widespread 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 (see CD4 count) 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.

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.

Skin infections

Other types of mycobacteria, usually Mycobacterium marinum, grow in swimming pools and even in home aquariums. These mycobacteria can cause skin infections.

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

Skin infections may clear up without treatment. However, 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 (Buruli ulcer) is the third most common mycobacterial disease in people with a normal immune system, after leprosy and tuberculosis.

At first, the legs, arms, or face swells. The swelling is painless and may cause a lump or be more generalized. The swollen area may develop into open sores and result in widespread destruction of the skin and underlying tissues.

The infection is treated with antibiotics and often surgery.

Another type of mycobacteria, Mycobacterium fortuitum, can infect wounds, tattoos, and artificial body parts, such as a mechanical heart valve or a breast implant. Antibiotics and surgical removal of the infected areas usually cure the infection.