FALSE POSITIVES HINDER TB TESTS

Tuberculin skin tests (TST) performed on people vaccinated with BCG may show a false positive result, causing difficulty when interpreting results. Investigators in Canada carried out a meta-analysis of prospective studies looking at TST results and BCG vaccination status. Vaccination was found to make a positive TST more likely but the effect of vaccination was less after 15 years. The authors suggest that if a positive skin reaction is greater than 15 mm in size then it is more likely to be a result of tuberculosis infection than BCG vaccination. They recommend that BCG history should be taken into account when interpreting a TST. (

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RISKY FACTORS SURFACE FOR DRUG RESISTANT TB

Immunocompromised status, advanced age, and failure to culture within 30 days, or to apply appropriate treatment, influence poor mortality from multidrug resistant tuberculosis (MDRTB). TB is a major cause of morbidity and mortality, and MDRTB (resistance to at least isoniazid and rifampicin) is a serious global problem, affecting 1%–4% of new TB patients. Researchers followed up 90 UK MDRTB cases over 18 months. They found that immunocompromised patients were nine times …