1. Introduction

Tuberculosis (TB) is an airborne infectious disease caused by Mycobacterium tuberculosis bacilli. Infection can be spread from one person to another through respiratory droplets (droplet nuclei) expelled by coughing, sneezing or laughing. Inhalation of infectious droplets can cause TB infection.

Most of the people are able to eliminate/control the infection by their immune system. They have latent TB infection, which is asymptomatic and is not contagious. However, if not treated some may develop active TB disease. Active TB disease is symptomatic, can affect many organs and if it presents as pulmonary or laryngeal disease, it can be spread to other people.

The risk of developing active TB disease remains life-long, but is the highest in the first years after the infection.  HIV positive people have a 20-30 times higher risk of developing active TB disease in comparison with people who are HIV negative. Worldwide, tuberculosis is the main opportunistic infection and the main cause of death among people living with HIV. 

Drug resistant TB (DRTB), can be defined as multidrug resistant (MDRTB) when resistance to rifampicin and isoniazid, with or without resistance to other first-line drugs. Extensively drug resistant tuberculosis (XDRTB) is defined as resistance to at least isoniazid and rifampicin, and to any fluoroquinolone, and to any of the three second-line injectables (amikacin, capreomycin, and kanamycin).