Tuberculosis (TB) is one of the most common infections in the world. About 2 billion people are infected with TB and nearly 3 million people are killed by it each year. In Canada, there are about 1,600 new cases of TB every year.
The bacterium that causes TB is called Mycobacterium tuberculosis. Someone can become infected and yet not have any symptoms of the active disease - this is called inactive TB.
For someone with a healthy immune system, there's only a 10% lifetime chance of the TB bacteria reactivating and causing the active symptoms of TB. If the immune system has been weakened because of HIV (human immunodeficiency virus) or other illnesses, the risk of moving from an inactive infection to an active symptomatic disease increases to 10% per year.
Babies, preschool children, and seniors are also at greater risk due to weaker immune systems.
Only people who have active TB infections can spread the TB bacteria. Coughing, sneezing, even talking can release the bacteria into the surrounding air, and people breathing this air can then become infected. This is more likely to happen if you're living in close quarters with someone who has TB or if a room isn't well ventilated.
Once a person is infected, the bacteria will settle in the air sacs and passages of the lungs and, in most cases, will be contained by the immune system.
Your chances of becoming infected are higher if you come from - or travel to - certain countries where TB is common. People who are at greater risk for TB infection include the elderly, homeless people, people with substance use problems, individuals who have spent time in a correctional facility, and people with weakened immune systems from HIV or AIDS (acquired immune deficiency syndrome). Of course, the odds increase if you have close or frequent contact with someone who has active TB symptoms. This is especially true for health care workers who may be exposed to patients with active TB.
The following factors may play a role in promoting active disease in someone who has an inactive TB infection:
There are no symptoms associated with inactive TB. This means that someone may have acquired the TB bacteria and yet show no signs or symptoms of infection. Symptoms only appear when the TB infection becomes active.
Symptoms develop gradually, and it may take many weeks before you notice that something's wrong and see your doctor. Although the TB bacteria can infect any organ (e.g., kidney, lymph nodes, bones, joints) in the body, the disease commonly occurs in the lungs.
Common symptoms include:
The occurrence of additional symptoms depends on where the disease has spread beyond the chest and lungs. For example, if TB spreads to the lymph nodes, it can cause swollen glands at the sides of the neck or under the arms. When TB spreads to the bones and joints, it can cause pain and swelling of the knee or hip. Genitourinary TB can cause pain in the flank with frequent urination, pain or discomfort during urination, and blood in the urine.