Tuberculosis is one of the world’s deadliest diseases, affecting up to a quarter of the global population. While it is less common in the United States than in other countries, it is highly contagious and is still a major health concern.
More commonly known as TB, tuberculosis is a bacterial infection that is spread through the air. Most TB infections start in the lungs, so when someone with the disease coughs or speaks, the bacteria can enter the air and be inhaled by people nearby. It settles in the lungs, where it can grow and move through the blood to other parts of the body. Without treatment, TB can be fatal.
However, not everyone who becomes infected develops the disease right away or at all.
“In some cases, the immune system fights the infection; instead of becoming sick with TB, these people have what is known as latent TB infection (LTBI),” says Zhaoyi Qin, MD, an internal medicine physician at Scripps Clinic Torrey Pines. “This means they have the bacteria in their bodies, but do not have active TB.”
People with LTBI don’t feel sick, nor can they spread the disease to others. Nevertheless, if their latent infection is not treated, they may develop TB in the future — especially if they have an HIV infection or a weakened immune system.
According to the Centers for Disease Control and Prevention (CDC), most TB cases in the US are caused by LTBI that becomes active. This can happen without warning, so it is important to get tested for the infection and learn if you may be at risk of infecting others.
“Testing is recommended, if not required, before starting a new job, transferring to a different school or volunteering,” says Dr. Qin. “Testing is especially important in schools, health care environments and other places where the risk of TB is increased because of close contact between people who may be ill or have weak immune systems.”
Two types of tests are used to detect TB bacteria in the body:
For the TB skin test, a liquid called tuberculin is injected into the skin of the forearm. Within two or three days, a health care professional checks the injection site for a bump or raised area that can indicate infection with the TB bacteria.
A blood test also can detect TB bacteria. The test measures how strong a person’s immune system reacts to TB bacteria by testing the person’s blood in a laboratory.
A positive TB test result means only that TB bacteria has been detected. It does not indicate whether the person has active TB or a latent infection. This requires additional testing.
TB disease can be diagnosed by medical history, physical examination, chest X-ray, and other lab tests.
Both TB disease and LTBI can be treated. TB disease is treated by taking several drugs as recommended by a health care provider. Treatment for latent TB is based on the person’s chances of developing TB disease. People at low risk for developing TB may not need treatment.