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TB Rapid Test Performs Well in Children
Overall, the Xpert MTB/RIF assay demonstrated high sensitivity and specificity; in smear-negative cases, a second induced specimen increased sensitivity from 33% to 61%.
The Xpert MTB/RIF, a new molecular test to identify Mycobacterium tuberculosis and rifampin resistance, performs with high sensitivity and specificity in adult populations (JW Infect Dis Apr 27 2011). Might it also work well for children, in whom diagnosis is complicated by low numbers of mycobacteria and difficulty in obtaining good specimens?
To find out, researchers conducted a prospective study involving children aged 15 years who were hospitalized in South Africa with suspected pulmonary tuberculosis (TB; N=452; 24% with HIV infection). After a 2- to 3-hour fast, sputum induction was done by a trained research nurse. Whenever possible, a second induced specimen was obtained later the same day or the following day. All specimens were cultured and also tested with the Xpert MTB/RIF assay.
Six percent of the children had a TB-positive smear, 16% had a positive culture result (defined as definite TB), and 13% had a positive MTB/RIF result. The initial MTB/RIF test detected all definite cases that were smear positive but only 33% of those that were smear negative; a second test (performed in 385 children) improved the detection of smear-negative cases to 61%. Overall, the sensitivity and specificity were 59% and 99%, respectively, for one MTB/RIF test, and 76% and 99% for two. MTB/RIF results were available within a median of 1 day (vs. 12 days for culture).
Comment: For detecting TB in children, the MTB/RIF test is substantially better than smear microscopy, especially when two induced specimens are examined. Although the WHO has recommended using a single MTB/RIF test in adults with suspected TB, the authors and an editorialist note the benefit (and the extra cost) of performing a second one in children whose first specimen tests negative. The authors point out the need for increased capacity for sputum induction in children — and the continued need for better methods to diagnose childhood TB.
— Mary E. Wilson, MD
Published in Journal Watch Infectious Diseases August 3, 2011
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