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Tuberculosis

From Mediwikis
Prevalence of TB internationally

This common, often lethal, infective disease is far more prevalent in third world and asian countries than in western countries. Some estimates say 1/3 of the world's population is infected, though these rates are declining.

Symptoms

5-10% of those infected with TB will develop symptoms (though there's an increased risk if co-infected with HIV)

General

  • Fatigue
  • Fever & Chills
  • Night Sweats
  • Loss of appetite
  • Finger Clubbing
Tuberculosis X Ray

Pulmonary

These are non-specific:

  • Chest Pain
  • Prolonged productive cough, sometimes with blood
  • Erosion of pulmonary artery may lead to massive blood loss
  • Particularly present in upper lung lobes

Extra-Pulmonary

If the disease moves outside of the lungs (as in children and immunosuppressed), extrapulmonary TB results, and symptoms depend on the site. Common sites include:

  • Pleura
  • CNS
  • Lymphatic system
  • Genitourinary system
  • Bones

Causes

Mycobacterium tuberculosis is the most common organism, being a small, slowly dividing aerobic bacillus, that can remain alive in a dry state for weeks. It is visible under a light microscope, and may weakly gram stain positive.
Other bacteria within the Mycobacterium tuberculosis complex (MTb) are:

  • Mycobacterium bovis
  • Mycobacterium africanum
  • Mycobacterium microti

Types

Pathogenesis of TB

Primary

After the first infection with MTb, the bacteria is absorbed by macrophages, but not digested. The bacteria proliferate within the macrophages, causing release of cytokines, leading to a delayed hypersensitivity type reaction. The end result is tissue necrosis and a granuloma forming around the infection site. The granuloma may heal, calcify, and cause the infection to lie dormant for years (the Ghon focus)

Secondary

Latent TB may be reactivated, years or decades later, by a number of factors:

  • Malnutrition
  • Becoming elderly
  • Immunosuppression, either by medication, or HIV co-infection
  • Diabetes mellitus
  • Chronic Kidney Disease

Spread

Spread via droplets when an patient with active disease (not latent) sneezes, coughs, or breathes. Those frequently exposed to TB patients are most at risk (22% infection rate). This is why partners and co-inhabitants of sufferers are treated with prophylactic anti-TB medication. Not all those who are infected develop active disease.

Investigation

  • Mantoux test-False positive may be returned in those with BCG immunisation
  • Quantiferon gold-
  • CXR- Cavitation, consolidation, calcification, fibrosis
  • Sputum culture showing Acid Fast Bacilli (AFB)- bronchoscopy or lavage if not spontaneous.
  • If systemic involvement is suspected, send samples of relevant fluids/ cavities.

Management

Prevention

TB is no longer routinely vaccinated against in the UK, as prevalence is low. It was originally performed using the BCG- the scars on the deltoid region many 18+ year olds have

Treatment

TB takes 6 months+ to treat, and the majority of relapses and long-term effects are due to poor concordance with medication. Directly Observed Therapy is therefore recommended by WHO- the patient takes their medication in front of a healthcare professional or family member, who monitors their attendance. Resistance to TB is also becoming a problem, and one individuals incomplete treatment may mean extensive drug resistance for a community of people that they infect.

Drugs

First Line

  • Ethambutol
  • Isoniazid
  • Pyrazinamide
  • Rifampicin