Mycobacterial infections (non-tuberculosis)

Notification requirement for mycobacterial infections (non-tuberculosis)

Notification is not required.

Primary school and children’s services centres exclusion for mycobacterial infections (non-tuberculosis)

Exclusion is not required.

Infectious agent of mycobacterial infections (non-tuberculosis)

Non-tubercular mycobacterial agents include Mycobacterium avium-intracellulare (also known as Mycobacterium Avium Complex, or MAC), M. kansasii, M. scrofulaceum, M. fortuitum, M. marinum, M. abscessus and M. chelonae.

See ‘Tuberculosis (mycobacterial infections) for infections due to M. tuberculosis, and see ‘M. ulcerans infections’ due to infections cause by M. ulcerans. Both of these are notifiable.

Identification of mycobacterial infections (non-tuberculosis)

Clinical features

MAC and M. kansasii are rare causes of lung disease in humans, and mainly affect middle-aged and elderly people with underlying chronic lung conditions. Disseminated MAC infection frequently occurs in people with advanced HIV, but is rare in immunocompetent hosts.

Cervical and submandibular lymphadenitis due to MAC, M. scrofulaceum and M. kansasii may occur in otherwise healthy young children.

M. fortuitum, M. chelonae and M. abscessus cause skin and wound infections and abscesses. They are frequently associated with trauma or surgery, particularly where prosthetic material is involved.

M. marinum causes ‘fishtank/swimming pool granuloma’, a nodular lesion that may ulcerate or cause nodular lymphangitis (sporotrichoid spread) and is usually located on an extremity.

Diagnosis

To establish a definite diagnosis of atypical mycobacterial infection, organisms must be cultured from a case with clinically compatible disease. Identification of acid-fast bacilli by direct smear on at least two occasions is highly suggestive of a mycobacterial infection. Histological examination of biopsies of clinical lesions may also assist in the diagnosis. Advances in gene probes and nucleic acid amplification procedures such as polymerase chain reaction (PCR) have allowed more rapid diagnosis of some mycobacterial infections, such as DNA probes for MAC and M. kansasii.

Clinicians who suspect infection with atypical mycobacteria should liaise with a pathology laboratory to ensure that clinical specimens are appropriately collected and transported.

Incubation period of mycobacteria

The incubation period of atypical mycobacterial infections can rarely be determined, but is probably weeks to several months.

Public health significance and occurrence of mycobacterial infections (non-tuberculosis)

Disease due to atypical mycobacterial infection is relatively rare. Cases of M. kansasii lung infection have occurred in western Victoria.

People with immunodeficiencies, pulmonary disease or tissue damage, such as skin trauma, may be at increased risk.

Atypical mycobacteria may colonise and infect people without causing clinical disease. Skin tests to tuberculin and other mycobacterial derivatives may be positive in such people.

Reservoir for mycobacteria

Mycobacteria, including many that are non-pathogenic to humans, are ubiquitous in the environment. Mycobacteria have been cultured from various environmental sources, including groundwater, dust and soil. Infection with M. marinum is associated with exposure to swimming pools, aquariums and other bodies of water. The environmental niches of many other mycobacteria remain unknown.

Mode of transmission of mycobacteria

The mode of transmission can rarely be determined for individual cases. Atypical mycobacteria are probably transmitted by aerosol from soil, dust or water, by ingestion, or in M. marinum and soft tissue infections by skin inoculation.

Person-to-person spread of atypical mycobacteria is almost unknown, with rare exceptions in the immunosuppressed and cases with bronchiectasis. Spread of M. abscessus between cystic fibrosis patients was strongly suggested by a United Kingdom study in 2013 (see ‘Additional sources of information’). M. avium-intracellulare causes disease in poultry and pigs, but animal-to-human transmission is rare.

Period of communicability of mycobacterial infections (non-tuberculosis)

Communicability of human cases is usually not a practical concern. Localised clusters of disease due to some atypical mycobacteria suggest that an established environmental focus of organisms may remain the source of infections for years.

Susceptibility and resistance to mycobacterial infections (non-tuberculosis)

With the exception of M. marinum infections and childhood lymphadenitis, atypical mycobacterial infections (in particular, MAC) are more common in patients who are immunocompromised or in those with chronic respiratory disease.

Control measures for mycobacterial infections (non-tuberculosis)

Preventive measures

As little information is known about the mode of transmission, the prevention of atypical mycobacterial infections is difficult. Environmental contamination of skin lesions may be reduced by some measures, such as wearing gloves and thorough handwashing when cleaning aquarium equipment to reduce the risk of M. marinum infection. Early medical advice should be sought in the event of skin lesions that do not heal.

People with advanced HIV infection and a low CD4 count are advised to take prophylaxis against MAC infection. Seek specialist advice.

Control of case

Cases of atypical mycobacterial infection usually require specialist management. Skin lesions and childhood lymphadenopathy are usually cured by surgery, sometimes in combination with anti-mycobacterial drugs.

Disseminated and pulmonary infections are treated with combinations of anti-mycobacterial drugs. The clinical outcome is strongly influenced by the underlying health of the host.

Control of contacts

No specific measures are needed for contacts of cases.

Control of environment

If infections can be linked with a specific environmental source, it may be possible to modify the environment or practices to minimise further transmission.

Outbreak measures for mycobacterial infections (non-tuberculosis)

Not applicable.