Page contents: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures

Victorian statutory requirement

Notification and school exclusion are not required.

Infectious agent

Mycobacterial agents include
M. avium-intracellulare complex (MAC), M. kansasii, M. scrofulaceum,
M. fortuitum, M. marinum and
M. chelonae.

For infections due to M. ulcerans see separate chapter.

Identification

Clinical features
MAC and M. kansasii are rare causes of lung disease in humans, and mainly affect middle-aged and elderly persons with underlying chronic lung conditions. Disseminated MAC infection frequently occurs in people with advanced HIV infection, 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 and M. chelonae cause skin and wound infections and abscesses. They are frequently associated with trauma or surgery.

M. marinum causes ‘swimming pool granuloma’, a nodular lesion that may ulcerate and is usually located on an extremity.

Method of diagnosis
Persons with immunodeficiencies or tissue damage such as skin trauma and pulmonary disease may be at increased risk of atypical mycobacterial infection. Clinicians who suspect infection with atypical mycobacteria should liaise with a pathology laboratory to ensure that clinical specimens are appropriately collected and transported.

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. Recent advances in gene probes and nucleic acid amplification procedures such as polymerase chain reaction (PCR) have allowed more rapid diagnosis of mycobacterial infections such as DNA probes for MAC and M. kansasii.

Incubation period

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

Public health significance & occurrence

Disease due to atypical mycobacterial infection is relatively rare. Cases of
M. kansasii lung infection have occurred in western Victoria in recent years. Infection with M. marinum is associated with contact with swimming pools, aquariums and other bodies of water.

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

Reservoir

Mycobacteria are ubiquitous in the environment, including many that are non-pathogenic to humans. Mycobacteria have been cultured from various environmental sources including ground waters, dust and soil. The environmental niches of many others remain unknown.

Mode of transmission

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 infections by skin inoculation.

Person to person spread of atypical mycobacteria is rare except in people who are immunosuppressed.

M. avium-intracellulare causes disease in poultry and pigs but animal to human transmission is rare.

Period of communicability

Communicability of human cases is usually not a practical concern except in cases of co-existing HIV infection. Localised foci of disease due to some atypical mycobacteria suggest that an established environmental focus of organisms may remain the source of infections for years.

Susceptibility & resistance

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

Control measures

Preventive measures
As little information is known about their mode of transmission, prevention of atypical mycobacterial infections is difficult. Environmental contamination of skin lesions may be reduced by some measures, including the wearing of gloves and thorough hand washing when cleaning aquarium equipment (for M. marinum). Early medical advice should be sought in the event of skin lesions that do not heal.

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

Not applicable.