Tuberculosis is a widespread bacterial disease, and while it is treatable, its eradication is being held up by the problems with finding those people who have latent infection. Researchers at Yonsei University, Republic of Korea, have created a multiple-target, real-time RT-PCR (reverse transcription polymerase chain reaction) assay that can distinguish between active disease and latent tuberculosis infections (LTBI). The results were published in Journal of Molecular Diagnostics.

Tuberculosis x ray

Commonly used tests for tuberculosis (TB), such as the tuberculin skin test (TST) or interferon-gamma release assays (IGRAs), can identify those people with tuberculosis infection, but can’t differentiate between active and latent infection or predict the chance of reactivation.

“The World Health Organization reports that one third of the world’s population is latently infected with Mycobacterium tuberculosis (MTB). It has been estimated that in 5% to 10% of LTBI individuals, the infection progresses to an active disease state, and the conversion rate is greater in immunosuppressed individuals such as those with HIV,” says Hyeyoung Lee of Yonsei University. “Therefore, rapid diagnostic tests and effective treatment of LTBI are important to reduce and control the TB burden.”

The Korean researchers looked at eight human immune markers, individually and in combination:

  • Th1-type factors [IFN-?, TNF-?, and IL-2R]
  • Th2-type cytokines [IL-4 and IL-10]
  • IFN-g-induced chemokines [CXCL9 (MIG), CXCL10 (IP-10), and CXCL11 (I-TAC)]

The team tested the assay using three different study groups (28 patients with active pulmonary tuberculosis; 22 patients with latent tuberculosis infections; and 29 non-TB controls). They found that TNF-? and CXCL9 were the best individual markers for differentiating between the three groups. The most effective combination for diagnosing TB and differentiating between active and latent disease was TNF-?, IL-2R, CXCL9, and CXCL10.

“These results imply that a combination of suitable single markers is very useful for the efficient diagnosis and differentiation of Mycobacterium tuberculosis infection,” says Lee.

While this study did not used xxpress PCR technology, the device’s speed and accuracy could make it a potential tool for near-patient diagnostics.