A summary of the clinical importance of presentation of tuberculosis, including subjects such as the causative agent, transmission, pathogen life cycle, pathology of infection, clinical symptoms, laboratory diagnosis and prevention/ treatment
- TB is a bacterial infection of the lungs and respiratory system, killing around 1.7 million
people a year (WHO 2016)
- Despite being rare in developed countries, the disease in still very common in developing
countries. Prevalent areas include sub-Saharan Africa, India, Southeast Asia and Latin
America
- Risk factors of TB include diabetes, end-stage kidney disease, malnourishment and some
cancers. TB is also the leading cause of death for HIV positive patients
Pathophysiology of Tuberculosis
- Causative agent is Mycobacterium tuberculosis – highly infectious bacteria which is highly
aerobic and is noted for a covering of mycolic acid, which makes gram staining very
difficult. Instead, acid-fast stains such as the Ziehl-Neelsen stain are used.
- M. tuberculosis has a notably slow growth rate, dividing every 18-24 hours.
- Humans are the only known reservoirs for this pathogen, and the main route of spread is by
air droplets from an infected person by coughing, sneezing and speaking.
- Latent TB – an inactive form where patients experience no symptoms. M. tuberculosis can
be dormant for several years before developing into the active form of the disease
- Tuberculosis presents as two forms: pulmonary tuberculosis and non-pulmonary
tuberculosis. Pulmonary tuberculosis is primarily an infection of the lungs, whereby the
bacteria are mainly found in the lobes of the lungs. The infection eventually forms what is
known as a Ghon Complex, which leads to calcification and fibrosis scarring of lung tissue
- Non-pulmonary tuberculosis presents in many forms, including tuberculous lymph glands,
tuberculous meningitis and tuberculosis of bones and joints
- Symptoms include coughing up blood or sputum, pain when coughing, unexplained fatigue,
night sweats and fever
Laboratory diagnosis
- Large specimen volume is needed as acid-fast bacilli are often sparse, even with patients
displaying obvious clinical features
- Decontamination of specimen to remove other pathogens such as streptococci
- Ziehl-Neelsen stain for analysis of suspected mycobacterial colonies
- Anti-tuberculous drug sensitivity testing
- Purified protein derivative (PPD) skin test/ Skin testing for tuberculin hypersensitivity
- Chest X-ray
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