tailieunhanh - Testing for tuberculosis

Various factors are associated with an increased risk of becoming infected and subsequently developing disease (Table 1 and Fig. 1). Transmission is most efficient in poorly ventilated, crowded environments. Droplets become diluted once they enter the external environment and M. tuberculosis is rapidly destroyed by ultraviolet radiation. Following lung infection, multiplication and dissemination of the organism is contained once cell-mediated immunity develops at 2–12 weeks. The risk of an individual progressing to active disease in the months and first few years after infection depends on the bacterial load and the effectiveness of their immune defences. A depressed immune response at the time of infection increases the risk for progressive primary (including disseminated) disease. If. | Diagnostic tests Testing for tuberculosis Anastasios Konstantinos Director of Queensland TB Control Centre Specialised Health Services Queensland Health Brisbane Summary Tuberculosis is caused by Mycobacterium tuberculosis. The approach to testing for tuberculosis depends on whether the aim is to diagnose active disease or latent infection. If active disease is suspected it is important to identify the site of disease. Analysis of sputum specimens for mycobacteria should precede other tests. 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. Key words diagnostic imaging interferon gamma release assays tuberculin skin tests. Aust Prescr 2010 33 12-18 Introduction Approximately 1000 new cases of tuberculosis or TB are diagnosed in Australia each year. Most of these patients were infected overseas and recent transmission within Australia is rare and limited to small clusters. Nevertheless primary care clinicians need to remain aware of tuberculosis because early diagnosis and treatment prevents transmission. Screening for latent tuberculosis is recommended before prescribing immunosuppressive therapy such as tumour necrosis factor alpha inhibitors cancer treatment and transplantation. Patients with a high risk of tuberculosis reactivation see Table 1 particularly those with HIV infection should also be tested for tuberculosis. Natural history of tuberculosis Fig. 1 Tuberculosis in humans is mainly caused by Mycobacterium tuberculosis. The infection is transmitted by respirable droplets generated during forceful expiratory manoeuvres such as coughing. Tuberculosis infection can be either active or latent. People with active infection have signs or symptoms caused by actively replicating tubercle bacilli. If this is in the lungs they are potentially contagious and usually have symptoms such

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