Recent Advances in Tuberculosis Diagnosis: IGRAs and Molecular Biology

Tuberculosis (TB) is one of the most deadly, curable infectious diseases. In 2012, the World Health Organization (WHO) reported 8.6 million new TB cases and 1.3 million deaths. Despite intensive research to improve tuberculosis diagnosis and drug susceptibility testing, TB still remains one of the most threatening curable infectious diseases. Effective control of TB remains in prevention, the immediate detection of Mycobacterium tuberculosis and rapid detection of drug-resistant strains, followed by prompt implementation of an adequate anti-tuberculous therapy. Providing rapid antibiotic resistance detection systems is essential to treat accurately the patients, especially with the emergence and spread of drug-resistant TB. In 2012, WHO reported 84,000 confirmed multi-drug-resistant TB cases worldwide, and 9.6 % of these cases were extensively drug-resistant TB. However, conventional techniques for culture isolation and antibiotic susceptibility testing are slow. In recent years, the molecular basis of resistance to anti-tuberculous drugs has been elucidated. Molecular methods based on sequencing have been used to detect the main mutations involved in resistance from isolated strains and clinical samples. New molecular methods have been developed to detect the most common mutations conferring M. tuberculosis resistance. Furthermore, the diagnosis of the latently infected people allows measures to prevent them from developing the active disease, and thus help break the chain of transmission of the microorganism. The tuberculin skin test, the classical method for diagnosing latent TB infection, has several drawbacks: low specificity, and also a low sensitivity in immunosuppresed patients. The development of the IFN-γ release assays (IGRAs), with a recognized higher specificity, has improved the diagnosis of latent TB infection. However, for the correct use and interpretation a close cooperation between physicians and expert microbiologists is required.