TB-causing bacteria is passed from person to person through the air when someone with the disease coughs or sneezes. People who are nearby may get infected after breathing in bacteria. The bacteria can attack any part of the body, but they usually stick to the lungs.
People with TB disease are most likely to spread it to those they spend time with every day, like their family or co-workers.
Pulmonary tuberculosis, or TB of the lungs, is the most common form of TB. TB can also attack the spine, bones and joints, the central nervous system, the gastrointestinal tract, the lymph system, and the heart.
Only 5 to 10 percent of healthy people who come in contact with TB bacteria will ever get sick. The vast majority of them will live with dormant TB bacteria in their bodies throughout their lives, because their immune systems are able to fight the bacteria and stop them from growing. People with latent TB don't feel sick, don't have symptoms, and can't spread TB. However, the bacteria remain alive in the body and can become active later. They have what are called latent infections.
TB is spread through the air, not through handshakes, sitting on toilet seats, or sharing dishes and utensils with someone who has TB. However, casual exposure is not sufficient for someone to get TB.
If at some point in their lives their immune system is weakened, the once-dormant bacteria may begin to grow again and cause active tuberculosis. Sometimes, doctors will recommend that people with latent TB infections take medicine to prevent development of active disease. The medicine is usually a drug called isoniazid (INH), which kills the TB bacteria that are in the body. Usually the course of treatment is six to nine months. Children and people with HIV infection, however, sometimes have to take INH for a longer period of time.
Latent TB infection A person with a latent TB infection has no symptoms and does not feel sick. They cannot spread TB to others although if they are tested for it, the test will indicate that they have been exposed to the bacteria. Chest x-rays and sputum tests will be negative. In latent infection, the immune system “walls off” the bacteria, which form a thick, waxy coat and can lie dormant that way for years.
Active TB infection A person with active TB has symptoms, including cough, chest pain, coughing up blood or sputum, weakness, fatigue, loss of appetite, chills, fever, and night sweats. They can spread TB to others, and a skin test for the disease will show positive results. They may also have an abnormal chest x-ray and/or positive sputum smear or culture.
TB bacteria become active if the body's immune system can't stop them from growing. They then multiply and make people sick. A small number of people get sick soon after they are infected, but most reactivate after years of latent infection.
Babies, young children, and people infected with HIV have weak immune systems and are more likely to develop active TB. Other conditions, like diabetes, leukemia, severe kidney disease, low body weight, and substance abuse, also can make a person more likely to come down with an active case of TB.
Symptoms of TB depend on where in the body the bacteria grow, but most of the time they grow in the lungs. When they do, the symptoms are …
Active TB is diagnosed by taking a sputum sample and seeing if TB bacteria grow in a culture. X-rays may also be used to show the presence of bacteria in the lungs.
Left untreated, a person with active TB will infect an average of between 10 to 15 people per year.