Many species of mycobacteria exist. The species Mycobacterium tuberculosis is the one that causes tuberculosis. The other mycobacteria species that cause disease are discussed here. These are called nontuberculous mycobacteria. People are usually exposed to these bacteria in the environment when they come in contact with contaminated water or soil. However, most exposures do not cause infection, and many infections do not cause disease.
When nontuberculous mycobacteria (NTM) infections do occur, they usually occur only in the following people:
Frail older people
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 tuberculosis infection, bronchitis, emphysema, or cystic fibrosis
NTM infections are typically 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 known as Mycobacterium avium complex (MAC), which includes Mycobacterium avium and Mycobacterium intracellulare. Other nontuberculous mycobacteria that are not included in MAC also sometimes cause infections in people.
Mycobacterium avium Complex (MAC) Infections
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.
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 may be removed surgically.
Widespread MAC infections
A MAC infection can spread throughout the body in the following people:
People with advanced AIDS
Sometimes 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.
People with severe AIDS and a CD4 count
Other Nontuberculous Mycobacteria Infections
Nontuberculous mycobacteria that are not included in MAC also sometimes infect people.
Skin infections
Swimming pool 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 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.
Buruli ulcer is a skin infection caused by Mycobacterium ulcerans. Worldwide, this infection (also known as Bairnsdale or Daintree ulcer) is a common mycobacterial disease in people with a normal immune system. 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 large, open sores on the legs or arms and resulting in widespread destruction of the skin and underlying tissues.
Mycobacterium ulcerans infection is treated with a combination of antibiotics.
Wound and foreign body infections
Other types of mycobacteria, 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 wounds, tattoos, and artificial body parts, such as a mechanical heart valve or a breast implant.
Mycobacterium abscessus caused outbreaks of severe infection when contaminated water was used to clean out root canals in children.
Antibiotics and surgical removal of the infected areas and/or foreign materials usually cure the infection. However, certain mycobacteria are difficult or impossible to eliminate, so some people are referred to an experienced specialist.
