Page content: Method of diagnosis | Mode of transmission | Incubation period | Period of communicability | Risk groups | Treatment

Method of diagnosis

• Clinical presentation
• Tuberculin skin test, using the Mantoux procedure
• Radiographic examination, sometimes including CT scans
• Bacteriolog - direct staining and culture of sputum or other specimens for the presence of M. Tuberculosis.
• Molecular amplification (PCR) and gene probes assist in rapid diagnosis.

Definitive diagnosis of TB rests on isolation of M. Tuberculosis (or M. Bovis) from sputum, urine, biopsy material, CSF or other clinical specimens. A negative sputum however, does not rule out a diagnosis of TB. Recovery and identification of mycobacterium from specimens has been made more rapid with test procedures such as the Bactec systems and DNA probes. Further information on these tests can be obtained from the Mycobacterium Reference Laboratory, VIDRL, Melbourne Health on (61 3) 9342 2674.

Mode of transmission

Infection occurs primarily by inhalation of aerosols produced by persons with pulmonary or laryngeal tuberculosis during coughing and sneezing. People in casual contact with infectious patients are at low risk. It is those in continuous close contact such as those living in the same household who are most at risk.

Bovine tuberculosis results mainly from ingestion of unpastuerised milk and dairy products and is uncommon in Australia.

Incubation period

From infection to the primary lesion, generally about 4-12 weeks.

Period of communicability

Theoretically, the patient is infectious as long as viable bacilli are being discharged from the sputum. In practice, the greatest risk of transmitting infection is in the period prior to diagnosis of an open case. A sputum smear positive case is more infectious than a culture positive case. The risk of transmitting the infection is significantly reduced within a period that can be from days to two weeks after commencing appropriate chemotherapy.

Special groups at risk

Immigrants and refugees from countries with a high incidence of tuberculosis. These countries include India, China, Vietnam, Philippines and Africa.

• Aboriginal people and Torres Strait Islanders.
• Immunosuppressed patients.
• Those with HIV infection and AIDS.
• The elderly.
• Diabetics.
• Drug and alcohol dependent people.
• Persons living in sub-standard, overcrowded conditions.
• Institutionalised persons, including prisoners.
• Health professionals.

Treatment

Adequate anti-TB chemotherapy for an appropriate period of time will result in a cure rate of almost 100 per cent. Short treatment regimes have been in use for some years; these involve the use initially of three or four drugs, namely isoniazid, rifampicin, pyrazinamide and possibly ethambutol and continuing with isoniazid and rifampicin for a further four months. Where there is evidence of drug resistance to INH or rifampicin or to both, short course anti-TB chemotherapy is totally inappropriate.

With the introduction of potent anti-TB drugs, hospitalisation of tuberculous patients is no longer mandatory unless social conditions or coexisting medical conditions dictate otherwise. The success of treatment relies heavily on patient compliance and direct supervision should be the aim of any treatment program. Compliance is important to prevent the development of drug resistance. For drugs used in the treatment of tuberculosis refer to: Streeton, J. & Patel, A. 1989, Tuberculosis in Australia and New Zealand into the 1990s, National Health & Medical Research Council, Canberra.