Tuberculosis (TB) is one of the most common infections in the world. According to the World Health Organization, in 2018 about 10 million people were infected with TB and 1.5 million people died from the disease.. In Canada, there are about 1,800 new cases of TB every year. Fortunately, global TB cases are decreasing by about 2% per 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 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 is higher.
Babies, preschool children, and seniors are also at greater risk of reactivation 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:
- age (children and seniors are more likely to develop the active disease)
- head or neck cancer
- illnesses that suppress the immune system, such as HIV or AIDS
- kidney disease
- long-term steroid use
- medications that suppress the immune system, such as anticancer medications (e.g., cyclosporine, tacrolimus)*
Symptoms and Complications
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:
- weight loss
- night sweats
- chest pain
- shortness of breath
- loss of appetite
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.
Making the Diagnosis
A tuberculin skin test allows a doctor to check your immune response to the TB bacteria. It is a test that is used for detecting infection with the TB bacteria. It is given to people who have been exposed to patients with active, contagious TB or to those in whom reactivation of TB is suspected.
Skin testing involves an injection in the forearm. 2 or 3 days later, a physician will "read" the test. If it's positive, indicated by a hard and swollen region at the site of injection, this means that your body's been infected by the TB bacteria. It does not necessarily mean that you have active TB – the TB may be inactive.
Chest X-rays can also be performed, and sputum samples can be analyzed in the lab. In these cases, the results are used to rule out or confirm active TB. Your doctor may also suggest other tests to confirm a diagnosis or to check for TB in other parts of your body.
Treatment and Prevention
Antibiotics are used to treat TB, since it's a bacterial infection. You may be hospitalized or told to avoid contact with other people until tests show that you're not contagious.
For TB lung infections, 3 or 4 antibiotics are combined for the first 2 months of therapy. 2 of these are then taken for another 4 to 7 months, depending on the number and type of antibiotics used as well as the sensitivity pattern of the TB bacteria that were cultured from the individual.
The antibiotics most commonly used include isoniazid, rifampin, pyrazinamide, and ethambutol. Most people will take medications every day for the first 2 months, then 3 times a week for the remaining treatment. It's important to take your medication as instructed by your doctor, and for the full course of the treatment. This helps to ward off types of TB bacteria that are antibiotic-resistant, which take longer and are more difficult to treat.
If a particular type of TB infection is resistant to regular antibiotic treatment, a combination of different medications must be taken for up to 24 months.
Once symptoms clear up, a doctor may re-test your sputum to see if the TB bacteria are still present. If you have a TB infection in other parts of your body (e.g., bones or joints), you may require treatment for more than one year. If you are taking isoniazid, your doctor may suggest that you take 50 mg of pyridoxine (vitamin B6) daily to prevent a side effect called peripheral neuropathy.
To prevent spreading TB, it's important to get treatment quickly and to follow it through to completion. This can stop transmission of the bacteria and the appearance of antibiotic-resistant strains.
A vaccine is available to limit the spread of bacteria after TB infection. The vaccine is generally used in countries or communities where the risk of TB infection is greater than 1% each year. It is used in newborns in these communities to prevent TB and its complications in the first few years of life. In Canada, this vaccine is not usually recommended. Research and development for a more effective vaccine is underway.
If a positive skin test is detected and other tests have confirmed that active TB is not present, your doctor may choose to prescribe a medication that prevents a TB infection from progressing to the active disease. The antibiotic most commonly used is isoniazid, which is usually taken daily for 9 months. Other medications that may be used include rifampin or a combination of isoniazid and rifapentine.
It is important to take your medications for as long as your doctor recommends. If you stop taking your medications before your doctor suggests, the TB infection can recur, you could get active TB, or the TB bacteria may become resistant to the medications you are taking.