Tuberculosis Guidelines Emphasize Newer Diagnostic Tests

Norra MacReady

December 08, 2016

Physicians should use new diagnostic tests whenever possible to assess patients for latent or active tuberculosis (TB) infection, according to updated guidelines developed jointly by the American Thoracic Society, the Infectious Diseases Society of America, and the Centers for Disease Control and Prevention.

The updated guidelines cover tests developed since the previous guidelines were published 17 years ago, including interferon-gamma release assays (IGRAs) and molecular diagnostics, according to an Infectious Diseases Society of America news release. David M. Lewinsohn, MD, PhD, professor of medicine at Oregon Health and Science University, Portland, and colleagues published the guidelines online December 8 in Clinical Infectious Diseases.

"These guidelines develop a structured approach to testing, recommending that doctors test for latent TB in patients who are at risk for infection and who would benefit from treatment, and for TB disease in patients who have signs and symptoms of the disease," Dr Lewinsohn said in the news release.

The authors used the Grading, Recommendations, Assessment, Development, and Evaluation (GRADE) approach to make 23 evidence-based recommendations regarding diagnostic testing for latent TB infection (LTBI), pulmonary TB, and extrapulmonary TB.

The goal of testing people suspected of having LTBI is to provide them with prophylactic therapy when appropriate, the authors write. High-risk individuals include immigrants from countries with a high burden of TB, residents and workers in high-risk settings such as prisons, people who work in mycobacteriology laboratories, and people exposed through household or other forms of contact.

The authors recommend diagnostic testing with an IGRA, rather than the standard tuberculin skin test (TST), in those with suspected LTBI who have a low or intermediate risk for disease progression and have received the Bacille Calmette-Guerin vaccine. IGRAs are preferable to the TST because they can be performed in a single visit and their specificity and sensitivity match or exceed those of the TST among people who have been vaccinated against TB.

However, IGRAs are expensive to perform and difficult to interpret, they require phlebotomy, and, in people who have not received the Bacille Calmette-Guerin vaccine, their accuracy may be no greater than that of the TST. Therefore, the authors state that the TST "is an acceptable alternative, especially in situations where an IGRA is not available, too costly, or too burdensome."

The guidelines recommend against testing those who are at low risk for infection and disease progression "because the risk of isoniazid chemoprophylaxis may outweigh the potential benefit. Despite this, testing is often performed in conjunction with school enrollment, employee health testing, and other institutional settings. In such patients, many conversions are false results, which may lead to unnecessary therapy and, therefore, unnecessary and age-related risk of hepatotoxicity," the authors write.

Once a diagnosis of LTBI is established, prophylactic treatment with isoniazid can reduce the incidence of TB disease in high-risk patients. Without treatment, someone with LTBI has a lifetime risk of 4% to 6% of developing TB disease.

IGRA and TST can detect infection, but they cannot distinguish between active and latent TB, the authors warn. "Therefore, the diagnosis of active TB must be excluded prior to embarking on treatment for LTBI." Usually this is accomplished by assessing for TB symptoms, such as ongoing fevers, night sweats, weight loss, and coughing; performing a chest radiograph; and conducting sputum testing.

Patients with signs of active TB disease should undergo smear, cultures, and molecular diagnostic testing, especially those at higher risk, such as patients with HIV or those who live with a patient with TB disease.

Patients with confirmed TB disease should receive treatment in conjunction with infectious disease and/or pulmonary specialists, along with the public health department.

TB is one of the major causes of morbidity and mortality in the world: The World Health Organization estimates that 8.6 million new cases occurred in 2014, with mortality reaching 1.5 million. Drug-resistant strains of TB first began emerging approximately 20 years ago, the authors write.

In the United States, the number of TB cases is declining, but 9412 cases of active TB were reported in 2014 and 11 million people are estimated to have LTBI.

"Without the application of improved diagnosis and effective treatment for LTBI, new cases of TB will develop from within this group, which is therefore a major focus for the control and elimination of tuberculosis," the authors warn.

The authors have disclosed no relevant financial conflicts of interest.

Clin Infect Dis. Published online December 8, 2016. Full text

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