TB Assignment

The transmission of of TB depends upon three factors; an infected person, an uninfected person (susceptible) and an air path for the droplet nuclei to travel to the susceptible person.

• The infected patient: Every infected person with TB is diversely infectious. How infectious a person is depends on the strength of their cough, how watery their mucus is and also the type of TB strain they are infected by. Also whether the the patient is under effective chemotherapy determines how infectious they are. Chemotherapy reduces the amount of droplet nuclei released when the patient, coughs, sneezes, or breathes.

Exposure time in the air: Usually a person must spend a long time with the the infected person in order to be infected by the mycobacterium TB, as the probability of being infected with the disease is proportional to the amount of time the droplet nuclei are exposed in the air. Therefore the risk is increased the longer that an uninfected person is in the company of an infected person.

• Finally; the environment: The environment can determine the risk of someone being infected. The characteristics of the environment will determine what path the droplet nuclei take when they have been released by the infected person. For instance if the uninfected person is in the company of the infected person in a small and confined space, it means that there is less ventilation, hence increasing risk of infection.

Incubation period for TB, and how it affects the spread of the disease

• The incubation period, the time it takes for a person to become infected after being exposed, varies from weeks to years, depending on the individual and whether the infection is primary, progressive or reactivation TB. Primary TB occurs when a person first becomes infected, this is when the body forms Tubercles on the lungs to contain bacteria; there are rarely symptoms with primary TB. Progressive TB is usually associated with Th2 T-cell response whereas a pure Th1 response mediates protection. Whereas in reactivation TB, the primary infection has resolved, but the bacteria are dormant or hibernating. When conditions become favourable for the bacteria, they become active again.

• The incubation period for this disease is a setback as this means that the carrier could have the disease for weeks-years and pass it on to many people without knowing that the are doing so.

Diagnosis of TB, and how it is treated.

• Symptoms of TB include: a persistent cough (usually for more than three weeks, at first may be dry and then is accompanied by sputum that may be blood-streaked, along with night sweats, weight loss, fever and tiredness.

• The test for Mycobacterium TB infection is a skin test called PPD (purified protein derivative).  Pieces of the bacteria are injected under the skin. If someone has been exposed to the bacteria in the past, the immune system will recognise it, leaving a large bump where the injection was done.  If this does happen, then more tests will have to be done. An X ray of the chest is done to look for signs of active disease followed by a series of other checks. If the bacteria are found it might be tested further to see if it is resistant to any of the drugs commonly used to treat tuberculosis. (continued)

• If someone has a positive PPD but does not have any signs or symptoms of the disease have a latent TB infection. If someone has a positive PPD and has signs and symptoms of TB, have an active TB. Treatment for active TB involves a mixture of antibiotics. PPD testing in people with HIV can be difficult because PPD testing does not test for the presence of Mycobacterium TB, but looks for signs that the immune system is currently fighting the bacteria. In HIV infected patients with compromised immune systems, the bacteria might be present but is not recognised by the immune system and as a result, may not show up when PPD is carried out.

• A combination of antibiotics successfully treats the infection. These must be taken for at least six months to avoid becoming ill with TB again and developing a drug resistant form of the disease.

What is the annual incidence of TB and where is the disease problematic?

• “Incidence” is the frequency of new occurrences of disease within a defined time interval. Incidence rate is the number of new cases of a specified disease divided by the number of people in a population over a specified period of time, usually one year. Therefore the incidence of Tuberculosis refers to the annual diagnosis rate or the number of new cases of Tuberculosis diagnosed each year.  These two statistic types can differ; a short lived disease like flu can have a high annual incidence, but a life long disease like diabetes has a low annual incidence.  
• Problematic countries where the incidence rate is high include India, where it was estimated to have 1, 835, 000 new case of tuberculosis in the year 2000. Also China has a high incidence rate; this was estimated to be at 1, 365, 000 new cases in the year 2000. The disease becomes more problematic in the lesser developed countries where they do not have the sufficient medical equipment and technology to vaccinate against it.