What Is It?
Tuberculosis (TB) is a bacterial infection that kills more than 2 million people a year. Most of these deaths occur in developing countries. The bacterium that usually causes TB in humans is Mycobacterium tuberculosis.
About one-third of the world’s population is infected with TB. However, most do not show signs of the disease. In these people, the bacteria are inactive (latent) and cannot be transmitted to others. If the body’s immune system weakens, however, TB can become active and cause disease. About 10 percent of people with the inactive form of the disease eventually will develop active tuberculosis.
TB was once a leading cause of death in the United States, but after the discovery in the 1940s of drugs to treat it, the number of TB cases declined. Today in the United States, health experts estimate that 10 million to 15 million people are infected with inactive TB. Many of these people were born in other countries and exposed to TB before coming to the United States. Other groups at higher risk of infection include the poor, the homeless and people who have been in prison or abuse substances.
Worldwide, TB is second only to HIV in causes of death by infectious disease among adults. In addition, many developing countries are suffering dual epidemics of TB and HIV. Because people with HIV have weakened immune systems, those with inactive TB infection are at high risk of developing active tuberculosis. In fact, TB is a major cause of death for people infected with HIV.
TB typically affects the lungs. But in up to one-third of infected people, the illness also involves other areas of the body. Common sites of infection include the lymph nodes, the membranes that cover the brain (meninges), the joints, the kidneys and the membrane covering the digestive organs (peritoneum).
TB bacteria are spread from person to person through the air. The bacteria are in droplets of secretions that come out of your mouth or nose when you cough or sneeze. One-time exposure to someone with TB is not likely to cause infection. Repeated or prolonged exposure is usually necessary. Touching someone with TB or sharing his or her utensils will not lead to infection, because the bacteria infect the lungs only when they are inhaled into the lungs
When infection occurs, a bacteria-filled droplet is inhaled into the deepest portion of the lung, where the bacteria reproduce (replicate) and spread through the body. At this point, the immune system generally can keep the bacteria from replicating any more, but usually cannot destroy them completely. The disease usually remains in this inactive or dormant state for life. People with inactive TB have no symptoms, and there is no way to tell they have been infected except for a special skin test.
In about 10 percent of people with inactive TB, the bacteria eventually manage to start replicating again, causing active TB. People whose immune systems are weakened by HIV are much more likely to develop active disease. Each year 5 percent to 10 percent of these people develop active TB.
Active TB occurs in several different forms:
- Primary pulmonary tuberculosis — In about 5 percent of people, the immune system can’t stop the initial TB infection. These people develop active TB within one year of exposure to the bacteria. This type of active TB is most common in infants and children, especially in developing countries with high rates of malnutrition and poor medical care. People with HIV and other diseases that suppress the immune system are also at risk.
- Postprimary (reactivation) pulmonary tuberculosis — About 95 percent of people infected with TB can inactivate the disease at first. Most of them never develop active disease. In those that do, the bacteria eventually overcome the immune system and begin to replicate and spread, usually in the lungs. The bacteria may destroy large areas of the lungs, forming cavities filled with bacteria and dead cells.
- Extrapulmonary tuberculosis — TB also can become active in other parts of the body, whether or not the lungs are involved. Common sites of infection include the bones, kidneys, lymph nodes and central nervous system.
- Disseminated or miliary tuberculosis — TB also can spread through the entire body by way of the bloodstream.
Most people infected with TB have inactive disease that does not cause any symptoms. However, a skin test for TB (called a PPD skin test, for “protein purified derivative”) often will turn positive within three months in these people.
Among people with active TB, symptoms vary according to the type of disease:
- Primary pulmonary tuberculosis — Some people, especially young children, with this type of TB have no symptoms other than fever and fatigue. Other symptoms can include:
- Chest pain
- Night sweats
- Poor appetite
- Problems gaining weight
- Postprimary (reactivation) tuberculosis — Symptoms include:
- Night sweats
- Weight loss
- Poor appetite
- Chest pain
- A general sick feeling
There usually is also a cough, which eventually produces discolored mucus. As the illness progresses, people may cough up blood, become short of breath and ultimately develop severe breathing problems.
- Extrapulmonary tuberculosis — Symptoms depend on where the TB has spread. For example, if TB affects the lymph nodes (about 25 percent of cases), it can cause swollen glands, usually at the sides and base of the neck. In tuberculosis of the bones and joints (about 8 percent of cases), there can be a hunchback curvature of the spine or pain and swelling of a knee or hip, usually with a limp. Genitourinary tuberculosis (about 15 percent of cases) can cause pain in the side (between the ribs and hip), frequent urination, pain or discomfort during urination and blood in the urine.
- Disseminated or miliary tuberculosis — Symptoms include:
- Night sweats
- Weight loss
- Lung problems (cough, shortness of breath, chest pain)
Although the bacteria are spread throughout the body, there may not be any other symptoms. But if there are, they can occur nearly anywhere. Some of the more common symptoms are:
- Visual difficulties
- Swollen lymph nodes
- Painful joints
- Scrotal masses
- Skin rashes
- Abdominal pain
Your doctor will ask you about symptoms such as cough, fever, weight loss, night sweats, swollen glands and breathing problems. He or she also will ask whether you have ever been exposed to anyone with TB, and if you have ever traveled to developing countries where TB is common.
Your doctor will examine you. He or she also will ask if you have ever had a tuberculosis skin test and what the results showed. If your doctor suspects that you have active pulmonary TB, he or she will have you get a chest X-ray. Your doctor also will have you cough up samples of mucus (sputum), which will be stained with special chemicals and then examined for the presence of bacteria. Your doctor also will perform a culture of the sputum, to see if tuberculosis bacteria grow. It will take several weeks to get the culture test result, because the bacteria grow slowly. People with extrapulmonary TB may have a normal chest X-ray and negative stains and cultures of their sputum.
Other body fluids (such as fluid from the space around your lungs or your abdomen) also may be tested for the presence of TB bacteria. A test called PCR (polymerase chain reaction) also can be used to check for TB infection.
Once someone’s healthy immune system has controlled a primary TB infection, the bacteria usually will remain inactive for life. A PPD skin test may be positive in these people, indicating a history of TB infection, but the lifetime chance of developing active TB disease is only about 10 percent.
If you develop active TB disease, it takes up to two weeks of treatment before you can no longer spread TB to other people. However, it takes at least six months to complete successful treatment. In some cases, patients are infected with strains of tuberculosis which are resistant to the most commonly used and effective antibiotics. These resistant strains can take up to 24 months to treat.
In the United States, the risk of TB exposure is greatest in medical facilities and in crowded or poorly ventilated institutions. If you live or work in one of these high-risk places, you should have regular PPD testing. If the test is positive, your doctor may recommend that you take the drug isoniazid (Laniazid, Nydrazid) for at least nine months. The drug will decrease your risk of developing active TB disease.
In developing countries with high rates of TB, a vaccine against the disease often is given at birth. The vaccine is not used routinely in the United States because the risk of transmission in this country is low, and because the vaccine is not very effective.
Doctors usually treat TB with a combination of four drugs — isoniazid (Laniazid, Nydrazid), rifampin (Rifadin, Rimactane), pyrazinamide (pms-Pyrazinamide, Tebrazid) and ethambutol (Myambutol) — for at least six months. Some may be given only for the first two months, and others for the full six months. It is very important that you take these medications as prescribed to prevent the bacteria from becoming resistant to the drugs.
TB strains that are resistant to isoniazid and rifampin (the two most effective TB antibiotics) are called multi-drug resistant (MDRTB). To cure MDRTB, patients must take combinations of “second line” TB medications — ethionamide (Trecator-SC), cycloserine (Seromycin), kanamycin (Kantrex) and others. These medications are more likely to cause side effects than the first-line drugs, and they are not as effective so they must be taken for up to two years.
In the past, it was felt that MDRTB was incurable in the developing world because the second-line drugs were too expensive, costing up to $15,000 per person per year. Now, however, these drugs can be obtained through the World Health Organization for as little as 5 percent of the prior cost, and treatment programs have been started in several developing nations.
Drug-resistant strains of TB have been found in every country worldwide, including the United States. Since 1993, 45 states and the District of Columbia have reported at least one case of drug-resistant TB.
When To Call A Professional
Call your doctor if you develop cough, fever, weight loss, swollen glands, night sweats or other symptoms of TB. You also should call your doctor if you have been exposed to someone with active TB. Ask your doctor about your need for routine PPD testing if you often travel to developing countries or work in an environment where TB risk is high, such as a medical facility or institution.
Tuberculosis that is not resistant to medication is nearly always curable, as long as patients comply with their treatment regimens, and antibiotics are started before major portions of the lung are destroyed. Patients who are infected with drug-resistant TB strains may have a lower cure rate, depending on which drugs they are resistant to, and how much lung damage they have before effective treatment is started.
Without proper treatment, more than half of people with active TB will die within five years.
Diseases and Conditions Center
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.