QuantiFERON-TB Gold Testing For Latent TB Eliminates False Positives From BCG Vaccination

Dr. Masae Kawamura MD Director and TB Controller City and County of San Francisco Department of Health Principal investigator for the Regional TB Training and Medical Consultation CenterMedicalResearch.com Interview with:
Dr. Masae Kawamura MD
Senior Director, QuantiFERON Medical and Scientific Affairs QIAGEN

MedicalResearch: What is the background for this study? What are the main findings?

Dr. Kawamura:  The report in The Lancet presents the baseline phase of China’s first large-scale, multi-center prospective study of the epidemiology of latent tuberculosis infection. The comparison study of more than 21,000 patients allowed detailed analysis of demographics and risk factors, along with robust comparisons within subgroups. The study’s follow-up phase is now underway, and patients with Latent Tuberculosis Infection (LTBI) will be evaluated for rates of disease and associated risks. Generally, up to 10% of people with Latent Tuberculosis Infection will develop active, contagious Tuberculosis (TB) disease at some point.

The overall TB infection rate was 18.8% measured by QuantiFERON-TB Gold compared to 28% by the traditional tuberculin skin test (TST), a difference of over 125 million people (based on 2014 population estimates from China). Unlike the tuberculin skin test, positive rates of QuantiFERON-TB Gold were not related to prior Bacille Calmette-Guérin (BCG) vaccination, but correlated with background active TB and suspect rates, as well as known risks for TB. BCG vaccination is recommended to newborns by the World Health Organization (WHO) as a matter of TB control policy in many countries, including China.        

MedicalResearch: What should clinicians and patients take away from your report?

Dr. Masae Kawamura:   A key take-away from this large study is that the Latent Tuberculosis Infection prevalence cannot be accurately assessed by the TST in countries with BCG vaccinated populations because of confounding of results by BCG and environmental nontuberculous mycobacteria (NTM). Due to the size of the study, the findings validate similar finding from numerous other smaller studies comparing the tuberculin skin test to QuantiFERON-TB Gold. This has profound implications for both public health programs and individual patients. From a public health perspective, the more accurate tool should be used to target resources on populations at risk for maximum impact and to avoid waste. From a clinical perspective, the overtreatment of individuals with falsely-positive tuberculin skin test is a patient safety issue and could be minimized using highly-specific IGRAs.  These findings challenge the recent 2014 WHO guidance on LTBI management that puts the tuberculin skin test and IGRAs on equal footing as diagnostic aids for LTBI.

The study also demonstrates that QuantiFERON-TB Gold, an ELISA-based assay, can be quickly scaled up for broad use in settings like China to implement the new WHO guidance.

MedicalResearch:   What recommendations do you have for future research as a result of this study?

Dr. Masae Kawamura: The findings offer valuable insights for TB control efforts, both in China and other areas of the world.  The follow-up study that is underway by Chinese investigators to examine the prevalence of new infection and disease rates from the baseline study is a logical next step to compare the two tools. However, interventional prevention trials based on the highest risk populations identified by these studies would accelerate knowledge while providing potential immediate benefit to the study populations and participating individuals.  Finally, cost effectiveness analysis from a societal perspective that compares tuberculin skin test to QuantiFERON-TB Gold based on the outcomes of these important studies would provide an important facet of knowledge for TB elimination efforts in China.

Citation:

Latent tuberculosis infection in rural China: baseline results of a population-based, multicentre, prospective cohort study

Gao, Lei et al.

The Lancet Infectious Diseases , Volume 15 , Issue 3 , 310 – 319

MedicalResearch.com Interview with: Dr. Masae Kawamura MD (2015). QuantiFERON-TB Gold Testing For Latent TB Eliminates False Positives From BCG Vaccination 

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