1 February 2010

Approximately 1000 new cases of tuberculosis (or TB) are diagnosed in Australia each year. While most patients become infected overseas and transmission within Australia is limited to small clusters, fast and accurate diagnosis is still important as TB can be highly infectious.  

Writing in the latest edition of Australian Prescriber, Dr Anastasios Konstantinos, Director of the Queensland Tuberculosis Control Centre, compares methods of testing for tuberculosis.

"The approach to testing depends on whether the aim is to diagnose active or latent tuberculosis infection," Dr Konstantinos says.

As active pulmonary tuberculosis is infectious, it is particularly important to consider the possibility of tuberculosis in patients with subacute and chronic infectious syndromes and with a cough for longer than two to three weeks.

"If active disease is suspected, it is important to identify the site of disease. Collection of sputum specimens for mycobacteria should precede other tests. Tuberculin skin tests and interferon gamma release assays have no role in the initial investigation for active pulmonary tuberculosis," Dr Konstantinos says.

When actively replicating tubercle bacilli are in the lungs the patient is potentially contagious and usually has symptoms such as cough, chest pain, shortness of breath, fatigue, weight loss, fever and night sweats.

If such a patient has an abnormal chest X-ray, analysis of three morning sputum specimens will rapidly detect those with active transmissible infection. If the patient has no respiratory symptoms, a normal chest X-ray almost excludes pulmonary tuberculosis.

Screening for latent TB is recommended before prescribing immunosuppressive therapy, cancer treatment and transplantation.

Those with latent infectionhave previously been infected but have no symptoms or evidence of disease and are not contagious. However, they remain at risk of developing active tuberculosis (reactivation) during their lifetime. Patients with a high risk of reactivation, particularly those with HIV infection, should be tested for tuberculosis.

"An infection should never be diagnosed as latent until active disease has been excluded. Tuberculin skin testing is recommended for diagnosing latent infection, but interferon gamma release assays may be useful in some circumstances," Dr Konstantinos concludes.

To view the full article go to www.australianprescriber.com

ENDS

Australian Prescriber is an independent peer-reviewed journal providing critical commentary on therapeutic topics for health professionals, particularly doctors in general practice. It is published by National Prescribing Service Limited (NPS), an independent, non-profit organisation for Quality Use of Medicines funded by the Australian Government Department of Health and Ageing.