TB Basics

What is tuberculosis (TB)?

Mycobacterium tuberculosis (MTB) is a type of bacterium (sometimes called a bug) that, for thousands of years, has caused the disease called tuberculosis (TB). TB, called consumption in the past, remains a major, if often unnoticed, problem today. TB is transmitted through the air when a person with TB sneezes, coughs, talks, laughs, or sings. There are many things we can do to reduce the spread of TB in health facilities and crowded places — infection control and early appropriate treatment are important to prevent disease transmission. Some people can be exposed to TB germs without becoming infected. Some can also become infected and not develop active disease — this is called latent TB infection (LTBI), and means that the immune system is able to contain the TB infection and prevent active disease. Active TB disease happens when TB infection overwhelms the immune system, and the bacteria begin multiplying and causing disease. Some symptoms of TB disease are cough, fever, weight loss, and night sweats. TB disease normally affects the lungs (called pulmonary TB), but it can also affect almost any organ in the body (called extrapulmonary TB). TB disease is preventable and curable, but can be fatal if not treated properly.

TB around the world

  • 1/3 of the world (2 billion people) is infected with TB bacteria
  • In 2013, there were an estimated 9 million new cases of active TB disease

   -- 13% (1.1 million) of those who developed TB were also living with HIV
   -- 6% (550,000) of those who developed TB were children

  • 1.5 million TB deaths were reported in 2013

   -- 360,000 TB deaths were in people with HIV
   -- 510,000 TB deaths were in women

TB and HIV

Globally, TB is the leading cause of death in people with HIV, accounting for nearly one in four HIV-related deaths. Because of their weakened immune systems, people with HIV are much more likely to develop active TB disease. For example, people living with HIV who have latent TB infection have a 1 in 10 chance of developing active TB disease each year; people without HIV who have latent TB have a 1 in 10 chance over their lifetime. TB is also more difficult to diagnose in people living with HIV, as their sputum samples often show no infection, even when one exists (known as being smear-negative). People living with HIV are more likely to have TB outside of the lungs. Some TB drugs cannot be used alongside certain HIV medications. People at high risk of HIV and their close contacts should be regularly monitored for symptoms and signs of TB. People with HIV and latent TB infection are urged to take medicine to prevent progression to active TB disease. Early initiation of antiretroviral therapy can also prevent progression to active TB disease in people living with HIV.

TB and children

Childhood TB is estimated to make up about 6 percent of the global incidence of TB (550,000 cases in children), though researchers from Brigham and Women’s Hospital and Harvard Medical School recently estimated that 1 million children develop TB annually– twice the number estimated by the WHO, and three times the number of children diagnosed each year– and, of those, 32,000 have drug-resistant TB.  Children most commonly present with TB between one and four years of age. TB infection in children is considered representative of recent and ongoing transmission within their larger communities; children are said to serve as a “sentinel” for incident cases. TB often occurs in children in the form of extrapulmonary TB. In addition, results from children’s sputum samples often show no infection (known as being smear-negative) even when children are infected, which makes them difficult to diagnose. Children usually respond well to treatment if started promptly, however the response is poorer for children living with HIV, a common coinfection in regions endemic for TB.

TB and women

TB is one of the top three causes of death among women ages 15–45 years, killing half a million women worldwide each year. TB causes between 6% and 15% of all maternal deaths. As TB can affect the genitals; it causes between 1% and 16% of overall infertility. Recent pregnancy is a demonstrated risk factor in developing active TB in women living with HIV. TB during pregnancy jeopardizes the mother, the fetus, and the newborn. Pregnant women with TB have increased complications during and after pregnancy. TB increases the likelihood of miscarriage, insufficient weight gain, premature labor, and the transmission of TB to the fetus during the pregnancy or birth. Newborns of mothers with TB are at an increased risk of death, low birth weight, and contracting TB after birth. Additionally, because people with compromised immune systems are at greater risk for contracting TB—women (and men) with other chronic conditions such as HIV and diabetes should be regularly screened for TB.

Drug-resistant TB

When TB-causing bacteria replicate, some may naturally change (mutate) and become resistant to anti-TB drugs. Treatment can then kill off the nonmutated bacteria, leading to the survival of only the mutated, drug-resistant bugs. Globally in 2013, it is estimated that 480,000 people developed drug-resistant TB. People with drug-resistant TB must resort to second-line drugs, which are more toxic, less effective, take longer to treat the disease, and are more expensive. Drug-resistant TB often develops when treatment is interrupted or when appropriate drugs required for treatment are unavailable. Drug-resistant TB can then be transmitted from person to person. It is difficult to treat, and new drugs are necessary to fight it.