Lurking in the dark: Latent Tuberculosis infection.

ABSTRACT

A subset of the tuberculous population has latent tuberculosis infection (LTBI). It is a condition wherein the affected individual is infected with Mycobacterium tuberculosis, but does not have any signs or symptoms of tuberculosis nor is he infectious to others. Risk of progression to active tuberculous infection is influenced by co-morbidities like HIV, diabetes, malignancy requiring chemotherapy, infants and children in close contact with susceptible individuals, and healthcare workers. Early diagnosis of LTBI is paramount. In addition to tuberculin test, Interferon gamma release assay (IGRA) is the new diagnostic modality that can be used for this purpose. Quantiferon-TB Gold In-Tube (QFTGIT) and T-SPOT TB are the two currently available IGRAs, of which the latter is slightly more preferred. More recently, TB PCR (Polymerase Chain Reaction) has aided accurate and early diagnosis of all forms of TB. While treating LTBI, it is observed that Isoniazid (INH) has stood the test of time and still prevails as the treatment of choice for active infection and for LTBI. Of course, adverse effects of INH and need for regular laboratory monitoring persist. Recently, moxifloxacin has been used as a substitute for INH. Newer drugs like rifapentine, nitromidazopyran, metronidazole and nitrofurans have all been tried with variable success and several clinical limitations, depending on comorbid conditions. India’s burden of extensive prevalence of TB is compounded by paucity of data on the same. The World Health Organization has estimated a mortality of 36 million by 2020 due to TB. This projection should encourage aggressive research into this entity.