Prevalence and Epidemiology of TB



Mycobacterium tuberculosis (TB) is said to have now infected over a third of the world's population - over two billion people (this figures includes both latent and active strains of TB) that will cause around two million deaths a year (World Health Organisation, 2010a), from a disease that was said to have been eradicated over three decades ago. The tuberculosis bacterium has been found in the spinal cord of the ancient mummies making it a very old disease going back as far as the Egyptians in 4000BC. Although it was not until 24 March 1882 when Robert Koch lectured his colleagues about his findings on the bacterium Mycobacterium tuberculosis that the world finally knew what they were facing (The Nobel Foundation, 2010).

Prevalence and Epidemiology

The number of incidences of TB has been increasing steadily for years because of a number of factors; these include patients that have been immunosuppressed for whatever reason particularly HIV/Aids and diabetes mellitus but also patients in general who have been hospitalised for whatever reason, numbers include those who are homelessness or are drug or alcohol abusers, also the popularity of world travel and immigration from countries with high number of diagnosed cases of TB should be included in the figures and also the fact that there is more resistance by the bacteria to antibiotics (hence we have MTB (multi-drug resistant TB) and XTB (extensively drug resistant TB)) (TB Alert Organisation, 2010, Knechel, 2009). The number of incidences, due to the World Health Organisation's Stop TB campaign are beginning to reduce the prevalence and number of deaths and has reduced the number of TB infections (World Health Organisation, 2010b) see table below.

Transmission and pathophysiology

TB is an airborne disease which is spread when a person infected with TB spreads droplet nuclei that contain the TB mycobacterium when they cough, talk, spit or sneeze at a person without the TB mycobacterium, even a person singing can spread TB (Knechel, 2009).

Our first line of defence against TB starts when the droplets are trapped in the upper respiratory system where mucus secreting goblet cells catch the bacilli and with the help of cilia present in the airways beat the trapped bacilli upwards and outwards (Knechel, 2009).

If this initial defence does not completely remove the droplets which contain the Mycobacterium tuberculosis it will then enter the alveoli of the lungs where a series of immunological events take place. The bacilli that reach the alveoli are engulfed by alveolar macrophages, a part of the innate immune system, which need no previous exposure to the bacteria to be able to attack and consume the bacilli. As part of this initial response the immune complement system activates the C3 protein which binds to the cell wall of the Mycobacterium tuberculosis. This enhances the recognition of the macrophages to the mycobacterium thereby increasing the phagocytosis of the bacilli (Knechel, 2009, Ferguson et al., 2004). Phagocytosis of the bacilli initiates a series of events that can result in the successful control of the infection (latent tuberculosis) or progress to an active form of tuberculosis (primary progressive or extrapulmonary). The outcome of which is determined by the strength of the defences produced by the immune system of the infected person thereby reinforcing the statement that those patients who are immunocompromised are more susceptible to TB.

The macrophages produce cytokines and enzymes that through a series of markers and regulators attract and work from the site of the macrophages T helper cells, namely IFN-? and natural killer cells, in an innate immune response (Nguyen and Pieters, 2007). These T-lymphocytes have been primed in the proximal lymph nodes and formulate granulomas around the bacilli (Nicod, 2007, Ellner, 1997). These granulomas contain the mycobacterium, dendrite cells and macrophages and restrict the replication and spread of the mycobacterium by producing a solid necrotic centre. And although our body's immune systems is able to produce such a strong response to the bacilli, some of the bacilli may survive the hostile environment of the granuloma and even possess the ability to change phenotype in order to survive (Knechel, 2009)(Nguyen and Pieters, 2007). It is these bacilli that survive and break through the wall of the granuloma and develop into primary TB (Knechel, 2009, Frieden et al., 2003).

After a period of two to three weeks the solid necrotic of the granuloma develops into a caseous (cheese-like) necrosis. This environment is also hostile to its inhabitants and restricts oxygen levels, has a low pH level and has little nutritional value thereby restricting growth of the mycobacterium and enhancing the latency. There is also further development of fibrosis and calcification of the granuloma to control the infection; bacilli can be imprisoned in the dormant healed lesions. These lesions can contain bacilli in a latent state throughout a person's life unless the strength and quality of their immune defences are compromised (Knechel, 2009, Frieden et al., 2003).

Signs and Symptoms

There are several different stages in TB; these include latent (as discussed above), primary disease and extrapulmonary (which also includes miliary TB)(, 2010). A person infected with latent TB will most likely present no signs or symptoms of the disease until the bacilli present in the necrotic material inside the granuloma are reactivated if the immune system becomes compromised. A tuberculin skin test is the most effective procedure used when latent TB is being diagnosed (Frieden et al., 2003) which has been used since the 1900s.

The stages of active TB can show unspecific signs of the infection although during the early progressive primary stage symptoms can include fatigue, malaise, weight loss fever and/or chills during the night. A cough may also commence that starts as non-productive but can progress to a productive expectorate with purulent sputum and have blood present once the disease progresses (Knechel, 2009).

The patient can also present weight loss, finger clubbing and anaemia (Knechel, 2009) when the TB progresses further. At this stage there are different types of tests for the diagnosis of extrapulmonary TB, which vary in price, speed and reliability. Most diagnosis is done through the testing of sputum, but can also include culture testing, radiographic images and drug susceptibility testing on patients with a persistent cough and who still have a positive culture after three months of treatment (Frieden et al., 2003).

In TB the most common area of infection is the lungs (pulmonary TB). If the disease spreads through the body (extrapulmonary TB) it can affect the central nervous system, the spine, abdomen, bones and joints, the heart's pleura, kidneys and genitourinary system {{2 Knechel, Nancy A. 2009/s38;8 Frieden, Thomas R. 2003/s892;}}. The treatment for these types of TB is generally the same as for pulmonary TB (Frieden et al., 2003).


The major drugs used in the treatment of TB are Isomazid, Rifampicin, Pyrazinamide, Ethambutol and Streptomycin (World Health Organisation, 2009).

The type and quantity of each drug administered depends upon the severity (pulmonary, extrapulmonary, military), type (MDR-TB or XDR-TB), person affected (child, adult, pregnant women etc) and any other underlying health issues the patient may have (HIV/AIDS, renal problems etc)(Frieden et al., 2003).

Treatment for TB may be drawn out over a long period of time and may involve up to a year of taking medication but if detected early and the drug regime adhered to the prognosis for a full recovery is extremely good. Most treatment will include and most likely cure 95% of cases using a drug regime which incorporates using two or more of the recommended drug treatments rather than just one and also a treatment that is fully overseen by medical staff (Frieden et al., 2003, World Health Organisation, 2009). With effective diagnosis and treatment the prevalence and mortality rates for Tuberculosis will decline in a positive and proactive means.


C3 protein - a key protein in the immune system also known as the complement component 3.

Caseous - cheese like.

Ghon Complex - calcified lesion filled with necrotic caseous material, may re-infect if patients immune system become compromised.

MDR TB - multi-drug resistant tuberculosis.

XDR TB - extensively drug resistant tuberculosis - MDR and XDR TB are two types of TB that come about because of treatment mismanagement and that do not respond to normal drug treatment.


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