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Tuberculosis

TB is a chronic infectious disease caused mainly by Mycobacterium tuberculosis (M. tuberculosis) and occasionally by Mycobacterium bovis or Mycobacterium africanum. These micro-organisms are also known as acid-fast bacilli (AFB) because of their staining characteristics.

TB is transmitted from one person to another through inhalation of droplets during coughing, laughing, talking, sneezing, and singing; however, coughing remains the most common means of transmission. Factors that contribute to an individual acquiring TB infection includes Concentration and size of infectious droplets, Extent of exposure (length of time the individual is exposed to the infectious droplets), Prevalence of TB in the community: the higher the prevalence of TB in the community, the higher the risk of exposure and infection, and Overcrowding and prolonged stay with an infectious person in a poorly ventilated and lighted environment. 

The risk of progression from infection to active disease depends on the status of the individual’s immune system. Only 10% of HIV-negative people infected with TB will eventually develop active disease in their lifetime because their immune system is strong enough to suppress multiplication of bacilli. Their TB infection therefore remains in the “dormant state”. Other groups of people have an increased risk of developing active TB disease following infection. These include: people with TB/HIV co-infection have an annual risk of 5-10% and a lifetime risk 20-30 times higher for developing TB disease, People with diabetes have a 1.5 times higher risk of developing TB disease than people without diabetes mellitus. Other risk factors for developing TB disease include: Malnutrition, recurrent infections of any kind, Substance abuse (alcoholism, drugs), Silicosis), Silicosis, Smoking, Age (very young or advanced), Long-term use of steroids and other immunosuppressive therapies, Poverty and Cancers.

Diagnosis of TB is through clinical suspicion based on a compatible history. A careful and extensive history-taking, which includes asking the patient questions relative to Symptoms suggestive of TB disease: cough for two weeks or more, night sweats, fever, and weight loss. If coughing, the sputum color and quantity, History of TB disease and the treatment outcomes, the presence of other medical conditions such as HIV/AIDS and diabetes mellitus, history of TB contact(s), Tobacco-smoking, including amount and duration of smoking. o History of substance abuse (drugs and alcohol), occupational history that may suggest exposure to silica dust, especially among miners.

Although no physical sign is sensitive or specific enough for TB, it is critical to assess patients for fever, look for anaemia, exclude lymphadenopathy, and confirm the presence or absence of chest and neurological abnormalities and hepato-splenomegaly in order to screen for comorbidities and rule out EPTB in all patients, including those with suspected PTB. Nearly a quarter of all TB patients may not have the classical five symptoms of TB, including cough, but are diagnosed based on an abnormal chest x-ray suggestive of TB.

Diagnosis of PTB depends on the identification of tubercle bacilli either by sputum smear microscopy or culture and identification of bacterial DNA using molecular techniques.

Sputum smear microscopy has been the cornerstone of TB diagnosis for more than a century. It remains the only affordable test in most low-income settings such as Tanzania. The test is relatively quick, easy to perform, and inexpensive.

TB treatment is initiated when the diagnosis has been confirmed. Effective TB treatment depends on use of the right anti-TB drug combinations in both the intensive and continuation phases, prescribed and taken in the correct doses according to the schedule and for the required length of time.