Editors' ChoiceGlobal Health

Tuberculosis Screening Method in Question

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Science Translational Medicine  19 Sep 2012:
Vol. 4, Issue 152, pp. 152ec169
DOI: 10.1126/scitranslmed.3004932

HIV infection greatly increases an individual’s risk of developing tuberculosis (TB). Indeed, without TB prophylaxis, 1 in 10 HIV-positive individuals exposed to TB develop active TB disease every year. TB prophylaxis with isoniazid therapy reduces the risk of developing active TB by more than 60% among HIV-positive individuals previously exposed to TB. However, if active TB is present, isoniazid therapy alone can result in resistance to the drug: Isoniazid needs to be combined with other TB medications to cure active TB. In low-resource settings, active TB is often excluded by asking questions in a defined protocol about active TB symptoms (fever, cough, night sweats, and loss of weight loss)—the WHO screen. Rangaka et al. have now evaluated the usefulness of the WHO screen for HIV-positive individuals on antiretroviral therapy (ART).

The investigators analyzed the results of TB symptom screening among 1429 HIV-positive persons, of whom 54% were on ART. They compared the WHO screen results with sputum culture from those individuals, which is the gold standard for diagnosing active TB. Contrary to their predictions, asking about symptoms was less sensitive among those on ART as compared with those awaiting ART (24% compared with 48%). If individuals reported symptoms while on ART, they were more likely to have active TB than those awaiting ART (94 versus 80%); however, 60% (76 of 126) of individuals with culture-positive TB had a negative question screening test. Adding body-mass index (BMI) increased the discriminatory ability of the WHO screen in both groups.

This finding is unexpected because ART improves immune function, and fighting active TB infection was expected to produce symptoms. Thus, the current recommended WHO protocol for excluding active TB before isoniazid therapy does not perform well, especially among HIV-infected persons on ART. New strategies need to be developed for excluding active TB, including adding BMI and lab values to protocols, but for now, sputum culture—where available—remains a valuable tool. Indeed, clinicians should be aware that patients, especially those on ART, may have active TB that is not excluded by screening for symptoms and use supplementary screening methods accordingly.

M. X. Rangaka et al., Effect of antiretroviral therapy on the diagnostic accuracy of symptom screening for intensified tuberculosis case finding in a South African HIV clinic. Clin. Infect. Dis., published online 5 September 2012 (10.1093/cid/cis775). [Abstract]

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