Top of page
Global Site Navigation

School of Medical and Health Sciences

Local Section Navigation

Help us improve our content by rating this page.

Page rating system

Please leave a comment about your rating so we can better understand how we might improve the page.

You are here: Main Content


Tuberculosis (TB) is a contagious disease. Left untreated, each person with active TB disease will infect on average between 10 and 15 people every year. But people infected with TB bacilli will not necessarily become sick with the disease. The immune system walls off the TB bacilli which can lie dormant for years.


Like the common cold, TB spreads through the air. Only people who are sick with TB in their lungs are infectious. When infectious people cough, sneeze, talk or spit, they propel TB bacilli into the air. A person needs only to inhale a small number of these to be infected.

When the inhaled tuberculosis bacteria enter the lungs, they can multiply and cause a local lung infection (pneumonia). The local lymph nodes associated with the lungs may also become involved with the infection and usually become enlarged. The hilar lymph nodes (the lymph nodes adjacent to the heart in the central part of the chest) are often involved. In addition, TB can spread to other parts of the body.


It may take many months from the time the infection initially gets into the lungs until symptoms develop. The usual symptoms that occur with an active TB infection are a generalized tiredness or weakness, weight loss, fever and night sweats. If the infection in the lung worsens, then further symptoms can include coughing, chest pain, coughing up of sputum and/or blood and shortness of breath. If the infection spreads beyond the lungs, the symptoms will depend upon the organs involved.


TB can be diagnosed in several different ways, including chest x-rays, analysis of sputum, and skin tests. Sometimes, the chest x-rays can reveal evidence of active tuberculosis pneumonia. Other times, the x-rays may show fibrosis or calcification in the lungs, suggesting that the TB is contained and inactive. Examination of the sputum on a slide can show the presence of the tuberculosis-like bacteria.

Several types of skin tests are used to screen for TB infection. These skin tests include the Mantoux test. In this test, a small amount of purified extract from dead tuberculosis bacteria is injected under the skin. If a person is not infected with TB, then no reaction will occur at the site of the injection (a negative skin test). If a person is infected with tuberculosis, a raised and reddened area will occur around the site of the test injection. This reaction, a positive skin test, occurs about 48-72 hours after the injection.

The TB skin test cannot determine whether the disease is active or not. This determination requires the chest x-rays and/or sputum analysis.

A blood test is now available to test immunity to TB. This test is called Quantiferon. Quantiferon replaces the Mantoux test which required multiple visits to the test centre or your GP. This test can be collected at the same time as the other required blood screening.


Bacille Calmette Guérin, also known as BCG, is a vaccine given throughout many parts of the world. It is derived from an atypical mycobacterium. There is controversy regarding the effectiveness of the vaccine.

Skip to top of page