Newer diagnostic tests for tuberculosis, their utility, and their limitations

Tuberculosis (TB) has remained a disease of public health importance since ages, affecting more than 10 million people globally and taking lives of 2 million people worldwide every year. Despite the dramatic improvements made in providing high-quality TB diagnostic services, since the discovery of the causative bacilli, many people with TB remain undiagnosed or get diagnosed only after long delays. Ten countries account for 77% of this gap and use only smear microscopy for diagnosis, which forms the backbone of TB diagnosis since 100 years. The challenge becomes onerous when disease gets associated with drug resistance, Human Immuno Virus (HIV) and other diseases in an environment where transmission is becoming easier by the day. It becomes of paramount importance to address this biggest public health challenge by delivering timely diagnosis using advanced technologies. Laboratory-based diagnostic approach to manage TB relies upon initial microscopic examination and clinical confirmations, with newer advanced diagnostic tools coming into play such as genotypic assays (line probe assay, cartridge-based nucleic acid amplification test, loop-mediated isothermal amplification) that are rapid molecular tests and culture methods (liquid culture media) with standard drug susceptibility testing assays. The program envisages correlating the rapid molecular diagnostics, which offers an impressive turnaround time of as low as around 2 h, with conventional standard methods to reinforce the diagnostic capacities. These also provide with august identification of drug resistance patterns for few most important first-line and second-line drugs that facilitate the early initiation of correct treatment. The latest developments have brought these tests to near-patient point of care. Culture tests (liquid culture media) are highest quality level gold standard techniques for the analysis of TB with its increased sensitivity over all others but requirement of dedicated facilities and infrastructure pushes it back the line. Finding a reproducible, efficient, cost-effective tool with minimal infrastructure requirements is an on-going search under TB diagnostics. This review addresses significant advances made in the diagnosis of infection, clinical disease, and drug resistance over the past decades.