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Researchers recommend interferon-gamma assay for latent tuberculosis testing in China
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Researchers in China reported that populations at high risk for tuberculosis in rural parts of the country, including those at high risk for reactivation of previous tuberculosis, should be tested for latent infection using an interferon-releasing assay instead of a tuberculin skin test.
“The WHO End TB Strategy, approved by the World Health Assembly in 2014, aims to end the global tuberculosis epidemic with targets to reduce tuberculosis deaths by 95% and to reduce new cases by 90% between 2015 and 2035. Management of latent Myobacterium tuberculosis infection in high-risk groups is a new priority action for the End TB Strategy,” Lei Gao, PhD, of the Ministry of Health Key Laboratory of Systems Biology and Centre for Tuberculosis at the Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, and colleagues wrote.
China, a country with a high burden of TB, developed new tools to address the epidemic, the researchers wrote.
“However, national guidelines on the management of latent tuberculosis infection have not yet been developed,” Gao and colleagues wrote.
The researchers performed a population-based multicenter prospective study between 2013 and 2015 at locations in rural China. Gao and colleagues performed a baseline survey in 2013, using QuantiFERON-TB Gold In-Tube as well as the tuberculin skin test to determine the prevalence of latent TB infection. In the follow-up phase, which lasted from 2014 to 2015, researchers tracked development from latent infections to active TB.
All patients were aged 5 years or older in 2013 and had lived at the study site continuously for at least 6 months in the past year.
A total of 7,505 participants tested positive for TB infection after baseline, the researchers wrote (QuantiFERON, n = 4,455; tuberculin skin test, n = 6,404; both, n = 3,354).
Gao and colleagues reported 84 incident cases of active TB during the follow-up period. Of these, 75 patients had been diagnosed with latent TB infection by QuantiFERON assay, 62 by tuberculin skin testing and 53 by both tests, the researchers reported. Patients who tested positive with QuantiFERON showed an incidence rate of 0.87 (95% CI, 0.68-1.07) per 100 person-years, 0.5 (95% CI, 0.38-0.63) per 100 person-years for those who tested positive with tuberculin skin testing and 0.82 (95% CI, 0.6-1.04) for patients who tested positive with both.
A history of (adjusted HR = 5.4; 95% CI, 3.34-8.71) and male sex (adjusted HR = 2.36; 95% CI, 1.3-4.3) were both associated with increased risk for disease development, the researchers wrote.
Jean-Pierre Zellweger, MD, of the TB Competence Center of the Swiss Lung Association, wrote in an accompanying editorial that “if a history of tuberculosis is a risk factor, this finding suggests that the first tuberculosis event was either left untreated or insufficiently treated,” and that it appeared difficult to apply Gao and colleagues’ findings.
“Radiological screening of large population groups to discover scars of spontaneously healed or insufficiently treated tuberculosis is probably not cost effective. [Tuberculin skin tests] or [interferon-release assays] in people without a known risk factor, such as immunodeficiency or recent contact with someone with tuberculosis, is probably not justified given the low predictive value of both tests.”
However, Zellweger wrote, an attempt to detect latent TB in vulnerable groups to prevent future tuberculosis would be “certainly justified.
“Use of [interferon-release assays] instead of [tuberculin skin tests] has advantages, even if the test is not perfect,” Zellweger wrote. “And taking all necessary measures to ensure the cure of all cases of tuberculosis, avoiding relapses and the development of drug resistance, would also be a wise decision.” – by Andy Polhamus
Disclosure: Zellweger reports teaching fees from Qiagen. The researchers report no relevant financial disclosures.
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