tuberculosis

Last reviewed 01/2018

Tuberculosis is the disease caused by infection with mycobacterium tuberculosis.

Tuberculosis is characterised by formation of tubercles and caseous necrosis in the tissues of any organ.

In man, the lung is the major seat of infection and the usual portal through which infection reaches other organs.

Patients with other species of mycobacterium are classed as atypical mycobacterial infections. However NICE considers the M. tuberculosis complex as M. tuberculosis or M. bovis or M. afrocami,.

NICE guideline provides guidance based on whether a patient has latent TB (evidence of previous infection and TB is dormant) or have active TB (an ongoing TB related illness such as pulmonary TB) (1):

• tuberculosis (TB) is a curable infectious disease caused by a type of bacterium called Mycobacterium tuberculosis ('M. tuberculosis' or 'M.Tb'), or other bacterium in the M. tuberculosis complex (that is, M. bovis or M. africanum)
  • spread by droplets containing the bacteria being coughed out by someone with infectious TB, and then being inhaled by other people
    
    
• initial infection clears in over 80% of people but, in a few cases, a defensive barrier is built round the infection and the TB bacteria lie dormant
  • called latent TB; the person is not ill and is not infectious
  • if the immune system fails to build the defensive barrier, or the barrier fails later, latent TB can spread in the lung (pulmonary TB) or develop in the other parts of the body it has spread to (extrapulmonary TB). Only a small proportion of people with latent TB will develop symptoms ('active TB')
    
    
• many cases of TB can be prevented by public health measures and, when clinical disease does occur, most people can be cured if treated properly. Taking medication in the wrong dose or combination, irregularly or for too short a time can lead to drug resistance
  • drug-resistant strains of TB are much harder to treat and significantly increase a person's risk of long-term complications or death. If left untreated, 1 person with active pulmonary TB may infect as many as 10 to 15 people every year
    
    
• TB incidence in the UK has increased since the early 1990s, but has remained relatively stable since 2005
  • despite this, it remains high compared with many other western European countries. Cases tend to cluster in urban areas where populations of at-risk groups are high. These include areas with many people born in countries with a high incidence of TB, areas with a high level of homelessness, poor housing or poverty, and areas with high rates of problem drug use

Reference:

• NICE (January 2016). Tuberculosis.