Groundbreaking clinical data published in the The Lancet medical journal showed that reliance on the 100-year-old tuberculin skin test has significantly overestimated latent tuberculosis infections in China, while results in the same patients using the QuantiFERON-TB Gold (QFT®) from QIAGEN N.V. provided a far better understanding of disease burden.
Results from the pivotal study, done by researchers at the Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing, found a far lower prevalence rate of latent TB as measured using QuantiFERON TB Gold than with the skin test (TST). The higher false positive rate created by the TST test - first developed and described by the German physician Felix Mendel in 1908 - is due to several factors including the use of the BCG vaccination in this country since the 1950s which has had only a very limited impact on reducing TB burden.
The results in particular showed a far lower overall TB infection rate of 18.8% measured by QFT compared to 28% using the TST in China, which has been estimated to have one million new cases of TB every year, more than any country except India.
The study - the largest-ever prospective multi-center study in China comparing diagnostics for latent tuberculosis infections - screened more than 21,000 people and aimed to identify at-risk populations to target for screening at the community level.
Given the new information on lower prevalence rates in China based on these study results, the study authors wrote that community-based preventive interventions for those with latent TB may be practical for individuals at risk for developing active TB.
"The present study represents a first step in China to address the important topic of development of tuberculosis control strategies," noted the study authors. "On the basis of evidence suggesting that BCG vaccination does not confer protection in adults, and the basic observation that most people in China who develop active tuberculosis are BCG vaccinated, it is clear that other tuberculosis control measures are needed. Screening of high-risk populations for latent tuberculosis infection with interferon-gamma release assays, and provision of preventive treatment for those testing positive and with high risks of developing disease, would be an important strategy to decease tuberculosis incidence."
"This study by top experts in China provides powerful evidence that the accuracy of the screening test truly matters for individual patients and public health, and that tackling the issue of latent TB infections is critical to eradicating this deadly disease. Consistent with other studies, QuantiFERON-TB Gold proved highly accurate and more reliable than the century-old skin test for correctly identifying TB infection.
The findings offer valuable insights for TB control efforts, both in China and other areas of the world," said Dr. Masae Kawamura, M.D., Senior Director, QuantiFERON Medical and Scientific Affairs at QIAGEN. "This study demonstrates that China is leading Asia in TB elimination by early adoption of prevention strategies in 2013 which have a focus on latent TB screening and by doing the necessary research to determine the preventive interventions that are needed."
QuantiFERON-TB Gold, introduced in China in 2014, is the modern standard for accuracy in latent TB infection diagnosis - faster, less labor-intensive and more accurate than the TST. The world's leading TB control programs are turning to QuantiFERON-TB Gold to replace the skin test because the superior clinical performance and significantly simpler administration of QFT as a laboratory-based blood test improve the cost-effectiveness of TB control programs and overall healthcare. Of note, the researchers in China selected QFT as the only IGRA to be used for their study.
Study provides insights on TB control
The report in The Lancet presents the baseline phase of China's first large-scale, multi-center 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 LTBI will be evaluated for rates of disease and associated risks. Generally, up to 10% of people with latent TB infection will develop active, contagious TB disease at some point. Already, independent experts report important implications for TB control:
"The study shows that historical estimates of latent TB infection in China, as high as 44.5% of the population, were overinflated by TST as compared to IGRA," said Dr. Lee Reichman, M.P.H., Executive Director of the Global Tuberculosis Institute at the New Jersey Medical School at Rutgers University. "While most TB control efforts in China so far have not focused on prevention, the research findings can guide policy makers to focus appropriate preventive interventions on the right people, which is a smaller group and based on the risk factors found in the study."
The overall TB infection rate was 18.8% measured by QFT compared to 28% by TST. Unlike the TST, positive rates of QFT 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 by the WHO as a matter of TB control policy to newborns in many countries, including China.
"Screening high-risk populations for LTBI infection using an IGRA and providing preventive treatment for those testing positive and with high risks of developing disease would be an important strategy to decrease TB incidence," the paper in The Lancet says. The study found higher latent TB rates in three vulnerable subpopulations - close contacts of active TB patients, the elderly, and smokers - and suggested that these groups "might be potential target populations for LTBI monitoring with preventive intervention due to the observed higher risk of LTBI prevalence among them."