Many species of mycobacteria exist. The species Mycobacterium tuberculosis is the one that causes tuberculosis of the lungs.
Other species of mycobacteria cause infections that are similar to the one caused by Mycobacterium tuberculosis, but these infections are not tuberculosis (TB). These other species are called nontuberculous mycobacteria (NTM).
People are usually exposed to NTM in the environment when they come in contact with contaminated water, dust, or soil. However, most exposures do not cause an infection, and many infections do not cause a disease.
When NTM infections do occur, they usually occur in the following people:
Frail older adults
People with a weakened immune system (such as those with HIV infection)
People with lungs that have been damaged by, for example, smoking for a long time, an old TB infection, bronchitis, emphysema, cystic fibrosis, or bronchiectasis
NTM infections are typically not contagious and are acquired from the environment rather than from infected people.
The main symptoms of some NTM infections are cough, fever, and weight loss.
The lungs are most commonly infected, and most lung infections are caused by a group of NTM known as Mycobacterium avium complex (MAC), which includes Mycobacterium avium and Mycobacterium intracellulare. Other NTM that are not included in MAC also sometimes infect the lungs. The lymph nodes, skin, and wounds are other sites that may be infected.
Mycobacterium avium Complex (MAC) Infections
Most NTM infections are caused by MAC.
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 (around 100.4° F [38° C]).
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 diagnose a MAC infection and distinguish it from tuberculosis (TB). A chest x-ray and a computed tomography (CT) scan are done. These imaging tests can show doctors some differences between TB and a MAC infection.
Because drug resistance is often a problem when treating MAC infections, doctors tend to give infected people a combination of 3 antibiotics, typically clarithromycin or azithromycin, rifampin or rifabutin, and ethambutol. Antibiotics are usually taken for 12 to 18 months. Doctors add other medications to the initial 3 antibiotics for people who have an infection that is not going away.Because drug resistance is often a problem when treating MAC infections, doctors tend to give infected people a combination of 3 antibiotics, typically clarithromycin or azithromycin, rifampin or rifabutin, and ethambutol. Antibiotics are usually taken for 12 to 18 months. Doctors add other medications to the initial 3 antibiotics for people who have an infection that is not going away.
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.
To diagnose the infection, doctors remove and test an affected lymph node.
Antibiotics are usually not necessary to cure the infection. Instead, the infected lymph nodes are removed surgically.
Widespread MAC infections
A MAC infection can spread throughout the body in the following people:
People with advanced HIV infection (also called AIDS)
Sometimes people whose immune system is weakened by other disorders, such as leukemia, or by medications
Symptoms include a fever, diarrhea, and abdominal pain. A widespread MAC infection also causes a low number of platelets in the blood (thrombocytopenia) and a low number of red blood cells or a low level of hemoglobin in the blood (anemia).
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 a combination of 2 or 3 antibiotics, often clarithromycin or azithromycin plus ethambutol and sometimes rifabutin.These infections are treated with a combination of 2 or 3 antibiotics, often clarithromycin or azithromycin plus ethambutol and sometimes rifabutin.
People with advanced HIV infection who were not aware of their HIV status before they developed a MAC infection are treated with a combination of antibiotics to first treat the MAC infection. Doctors may delay giving some people antiretroviral therapy (ART) for up to 2 weeks if they are concerned people will have an immune reaction from the treatments.
Other Nontuberculous Mycobacteria Infections
Nontuberculous mycobacteria (NTM) that are not included in MAC also sometimes infect people.
Skin infections
Swimming pool granuloma or fish tank granuloma is a skin infection caused by Mycobacterium marinum. Mycobacterium marinum and some other mycobacteria 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 properly 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 appear, enlarge, and turn purple. They usually occur on the hands, arms, or knees.
This skin infection may clear up without treatment, but antibiotics such as minocycline, doxycycline, and clarithromycin are effective.This skin infection may clear up without treatment, but antibiotics such as minocycline, doxycycline, and clarithromycin are effective.
Buruli ulcer (also known as Bairnsdale or Daintree ulcer) is a skin infection caused by Mycobacterium ulcerans. Most of these infections occur in West and Central Africa. In Australia, most cases occur in a temperate area around the city of Melbourne.
This infection does not cause pain. It starts as a lump under the skin, a large swollen area, or generalized swelling of the legs, arms, or face. As the infection progresses, large, open sores (ulcers) form on the legs or arms and the skin and underlying muscle and soft tissues are destroyed; when the infection is this severe, it can cause pain. As the skin and tissues heal, scars may form, and the muscles of the arms and legs may tighten in permanent, flexed positions called contractures.
Mycobacterium ulcerans infection is treated with a combination of antibiotics such as rifampin and clarithromycin.infection is treated with a combination of antibiotics such as rifampin and clarithromycin.
Wound and foreign body infections
Other species of NTM, such as Mycobacterium fortuitum and Mycobacterium abscessus, can survive in water systems in residential, office, and health care facilities. They are difficult to eradicate with common decontamination practices (for example, using chlorine in the water).
Mycobacterium fortuitum can infect penetrating eye and skin wounds and tattoos and can contaminate implanted medical devices, such as a heart valve made from the heart of a pig or breast implants.
In the United States, outbreaks of severe infection occurred in children when water contaminated with Mycobacterium abscessus was used during a dental procedure.
Doctors usually need to repeatedly clean and remove dead skin and replace the contaminated devices. Doctors also give people a combination of at least 2 antibiotics, and the antibiotics may need to be taken for 2 years or sometimes longer. However, certain NTM infections are difficult or impossible to cure, so some people are referred to an experienced specialist.
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