Tuberculosis (TB) is a disease caused by a bacterium called Mycobacterium tuberculosis.
Recently, new strains have emerged that are resistant to commonly used drugs. Like other bacteria, mycobacteria can undergo genetic changes (known as mutations), which can make them naturally resistant to an anti-TB drug. New advanced forms of the condition are known as multidrug-resistant TB (MDR-TB) or extremely-drug-resistant TB (XDR-TB).
This resistance is likely to occur through human errors, such as choosing the wrong drugs to treat the condition or people stopping treatment before the full course has been completed. The more an antibiotic is wrongly used, the more likely it is that the bacteria will mutate and be resistant to the drug.
Any organ of the human body can be affected by the disease, although the condition is most commonly diagnosed in the lungs.
The main symptoms of TB are:
- A reduced appetite
- Weight loss
- Night sweats
- Persistent cough
- Coughing up blood in an advanced stage
TB is an airborne infectious disease. It is spread through droplets in the air, via a sneeze or a cough from people infected with the mycobacteria.
The highest risk of developing the disease is among people who are closely and regularly in contact to someone with the disease. Research has found that children who have close contact with a contagious case have a 30-50% chance of developing TB.
Once persons are infected with the bacteria, they can rapidly develop the disease, where they are infectious, experience symptoms and require treatment. This generally occurs in children and people who have a weakened immune system. This is termed “primary TB”. Otherwise, a person will have a latent infection when they are not infectious and do not experience symptoms. 5-10% of people with a latent infection can develop active TB disease.
There are a number of factors that increase the risk of developing TB, including diabetes, exposure to drugs that suppressive the immune system and tobacco smoking. The most important risk factor is infection with HIV. The WHO states that the risk of developing tuberculosis is estimated to be between 20-37 times greater in people living with HIV than among those without HIV infection.
A vaccine known as BCG vaccine was introduced in 1921. This is known to help prevent some severe forms of the disease in children but it has unpredictable success in protecting against the lifelong risk of developing TB.
BCG is used to varying degrees across Europe with some countries vaccinating all children as they are born and others having discontinued mass vaccination programmes.
The World Health Organization (WHO) recommends that the best way to prevent TB is by successfully identifying cases and using antibiotics to treat the condition. WHO strategies, such as the Stop TB Strategy, have contributed to a reduction in the prevalence and incidence of TB worldwide.
The ultimate goal of international and national public health authorities is the elimination of TB, decreasing new infectious cases to less than 1 in every 1 million people by 2050, although at the time of publishing experts believe that authorities are unlikely to meet this target.
Samples of mucus or phlegm are taken from a person with suspected TB and tested for the bacteria. A chest x-ray, and sometimes an additional CT scan are helpful to confirm the disease is present.
Other tests such as the tuberculosis skin test and a whole-blood test, known as Interferon-Gamma Release Assay (IGRA), are helpful in diagnosing latent TB.
Treatment is aimed at curing the condition and avoiding the transmission of the disease to other people. Treatment is usually characterised by an intensive phase of treatment for 2 months, followed by a continuation phase for 4 months. The first phase usually includes four different drugs (isoniazid, rifampicin, ethambutol and pyrazinamide) and is designed to stop the bacteria growing. The second phase is designed to kill the remaining bacteria.
MDR- and XDR-TB require the so-called second-line drugs for at least 20 months; however, they are expensive, toxic and difficult to manage.