Tuberculosis (TB) is caused by bacteria (Mycobacterium tuberculosis) that most often affect the lungs. Tuberculosis is curable and preventable.
TB is spread from person to person through the air. When people with lung TB cough, sneeze or spit, they propel the TB germs into the air. A person needs to inhale only a few of these germs to become infected.
About one-third of the world’s population has latent TB, which means people have been infected by TB bacteria but are not (yet) ill with the disease and cannot transmit the disease.
People infected with TB bacteria have a 10% lifetime risk of falling ill with TB. However, persons with compromised immune systems, such as people living with HIV, malnutrition or diabetes, or people who use tobacco, have a much higher risk of falling ill.
When a person develops active TB disease, the symptoms (such as cough, fever, night sweats, or weight loss) may be mild for many months. This can lead to delays in seeking care, and results in transmission of the bacteria to others. People with active TB can infect 10–15 other people through close contact over the course of a year. Without proper treatment, 45% of HIV-negative people with TB on average and nearly all HIV-positive people with TB will die.
Who is most at risk?
Tuberculosis mostly affects adults in their most productive years. However, all age groups are at risk. Over 95% of cases and deaths are in developing countries.
People who are infected with HIV are 20 to 30 times more likely to develop active TB (see TB and HIV section below). The risk of active TB is also greater in persons suffering from other conditions that impair the immune system.
One million children (0–14 years of age) fell ill with TB, and 170 000 children (excluding children with HIV) died from the disease in 2015.
Tobacco use greatly increases the risk of TB disease and death. More than 20% of TB cases worldwide are attributable to smoking.
Global impact of TB
TB occurs in every part of the world. In 2015, the largest number of new TB cases occurred in Asia, with 61% of new cases, followed by Africa, with 26% of new cases.
In 2015, 87% of new TB cases occurred in the 30 high TB burden countries. Six countries accounted for 60% of the new TB cases: India, Indonesia, China, Nigeria, Pakistan, and South Africa. Global progress depends on advances in TB prevention and care in these countries.
Symptoms and diagnosis
Common symptoms of active lung TB are cough with sputum and blood at times, chest pains, weakness, weight loss, fever and night sweats. Many countries still rely on a long-used method called sputum smear microscopy to diagnose TB. Trained laboratory technicians look at sputum samples under a microscope to see if TB bacteria are present. Microscopy detects only half the number of TB cases and cannot detect drug-resistance.
The use of the rapid test Xpert MTB/RIF® has expanded substantially since 2010, when WHO first recommended its use. The test simultaneously detects TB and resistance to rifampicin, the most important TB medicine. Diagnosis can be made within 2 hours and the test is now recommended by WHO as the initial diagnostic test in all persons with signs and symptoms of TB. More than 100 countries are already using the test and 6.2 million cartridges were procured globally in 2015.
Diagnosing multi-drug resistant and extensively drug-resistant TB (see Multidrug-resistant TB section below) as well as HIV-associated TB can be complex and expensive. In 2016, 4 new diagnostic tests were recommended by WHO – a rapid molecular test to detect TB at peripheral health centres where Xpert MTB/RIF cannot be used, and 3 tests to detect resistance to first- and second-line TB medicines.
Tuberculosis is particularly difficult to diagnose in children and as yet only the Xpert MTB/RIF assay is generally available to assist with the diagnosis of paediatric TB.
TB is a treatable and curable disease. Active, drug-susceptible TB disease is treated with a standard 6 month course of 4 antimicrobial drugs that are provided with information, supervision and support to the patient by a health worker or trained volunteer. Without such support, treatment adherence can be difficult and the disease can spread. The vast majority of TB cases can be cured when medicines are provided and taken properly.
Between 2000 and 2015, an estimated 49 million lives were saved through TB diagnosis and treatment.
TB and HIV
At least one-third of people living with HIV worldwide in 2015 were infected with TB bacteria. People living with HIV are 20 to 30 times more likely to develop active TB disease than people without HIV.
HIV and TB form a lethal combination, each speeding the other’s progress. In 2015 about 0.4 million people died of HIV-associated TB. About 35% of deaths among HIV-positive people were due to TB in 2015. In 2015 there were an estimated 1.2 million new cases of TB amongst people who were HIV-positive, 71% of whom were living in Africa.
WHO recommends a 12-component approach of collaborative TB-HIV activities, including actions for prevention and treatment of infection and disease, to reduce deaths.
Anti-TB medicines have been used for decades and strains that are resistant to 1 or more of the medicines have been documented in every country surveyed. Drug resistance emerges when anti-TB medicines are used inappropriately, through incorrect prescription by health care providers, poor quality drugs, and patients stopping treatment prematurely.
Multidrug-resistant tuberculosis (MDR-TB) is a form of TB caused by bacteria that do not respond to isoniazid and rifampicin, the 2 most powerful, first-line anti-TB drugs. MDR-TB is treatable and curable by using second-line drugs. However, second-line treatment options are limited and require extensive chemotherapy (up to 2 years of treatment) with medicines that are expensive and toxic.
In some cases, more severe drug resistance can develop. Extensively drug-resistant TB (XDR-TB) is a more serious form of MDR-TB caused by bacteria that do not respond to the most effective second-line anti-TB drugs, often leaving patients without any further treatment options.
About 480 000 people worldwide developed MDR-TB in 2015. In addition, around 100 000 people developed resistance to rifampicin (the most effective first-line medicine) and needed MDR-TB treatment. The MDR-TB burden largely falls on 3 countries – China, India, and the Russian Federation – which together account for nearly half of the global cases. About 9.5% of MDR-TB cases had XDR-TB in 2015.
Worldwide, only 52% of MDR-TB patients and 28% of XDR-TB are currently successfully treated. In 2016, WHO approved the use of a short, standardised regimen for MDR-TB patients who do not have strains that are resistant to second-line TB medicines. This regimen takes 9–12 months and is much less expensive than the conventional treatment for MDR-TB, which can take up to 2 years. Patients with XDR-TB or resistance to second-line anti-TB drugs cannot use this regimen, however, and need to be put on longer MDR-TB regimens to which 1 of the new drugs (bedquiline and delamanid) may be added.
WHO also approved in 2016 a rapid diagnostic test to quickly identify these patients. More than 20 countries in Africa and Asia have started using shorter MDR-TB regimens. By the end of 2015, 70 countries had introduced bedaquiline and 39 countries had introduced delamanid, in an effort to improve the effectiveness of MDR-TB treatment regimens.
Photo Credit: Nigeria Health Watch