Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis. TB bacteria are spread by airborne droplets expelled from the lungs when a person with active TB disease coughs, sneezes or speaks. Repeated exposure to these droplets can lead to infection in the air sacs of the lungs.
The immune defenses of healthy people usually prevent TB infection from spreading beyond a very small area of the lungs by creating a barricade around the bacteria. This walled-up infection is called latent TB and may be present throughout a person's life. If the body's immune system is impaired because of infection with HIV (the virus that causes AIDS), aging, malnutrition or other factors, the TB bacteria may begin to spread more widely in the lungs or to other tissues. When this happens, it is called reactivated (or active) TB infection.
People with HIV are particularly vulnerable to reactivation of latent TB infections as well as to active disease caused by new TB infections. In the United States, nearly one out of ten people infected with both TB and HIV develops active TB each year. In more than half of the people with TB who also have AIDS, TB spreads to the lymph nodes, bone marrow, blood, liver, bones, kidneys, or skin.
Many of the symptoms of active TB resemble those of other diseases that commonly occur in people with HIV, or several infections may occur at the same time causing overlapping symptoms. The early symptoms of active TB include fatigue, weight loss, fever, chills and night sweats. Once the infection has progressed, people may develop a cough, chest pain or sputum that may contain blood. TB that has spread beyond the lungs causes additional symptoms, which vary depending on the tissues infected. TB of the spine may cause back pain, whereas TB of the kidneys can cause blood in the urine.
Diagnosis. Doctors initially diagnose active TB based on a patient's symptoms, a person's history of exposure to TB, x- rays that may show evidence of TB infection and a positive reaction to the TB skin test. The telltale signs of active TB usually seen in a chest x-ray are often absent in people who have HIV and active TB.
Doctors confirm a diagnosis of active TB by detecting TB bacteria in sputum, blood, or other body fluids or tissues. This can take several days to weeks, and doctors may decide to give TB medications before the results of their test are known. It is particularly important to determine if a person has TB that is resistant to the usual drugs used to fight TB. Drug-resistant TB is very serious and is difficult to treat.
Treatment. The initial treatment for HIV-infected people with active TB is two months of combination drug therapy with the antibiotics isoniazid, rifampin, pyrazinamide, and ethambutol or streptomycin. Treatment is continued for at least another seven months with more or fewer antibiotics, depending on how susceptible the strain of TB is to various drugs.
Although people with TB often feel better after a few weeks of drug therapy, it is important that they complete their full course of treatment. If treatment is stopped early, TB bacteria may develop the ability to resist the TB drugs. Treatment is effective in most people with HIV if their TB is not drug resistant.
Anti-TB drugs can have side effects including liver diseases. Because it is so important for people with HIV who are infected with TB to take these drugs, they should be sure to report any problems with the medications to their doctor or clinic and not discontinue taking them on their own.
Latent TB infection occurs without symptoms. It is diagnosed by a positive TB skin test, which can indicate if a person is infected with TB bacteria in the absence of signs or symptoms of active TB disease. People who have HIV should have a TB skin test annually. However, the skin test cannot distinguish between latent and active TB infection.
The TB skin test also may not be reliable in people with HIV because their suppressed immune systems may prevent them from testing positive even if they are infected with TB. On the other hand, false reactions can occur if people are infected with bacteria closely related to M. tuberculosis, including those that cause M. avium (MAC) infections, which are common in people with HIV.
Preventive Therapy for Latent TB. To avoid these development of active TB, doctors usually recommend that people with HIV and latent TB take anti-TB drugs for a year. People with HIV who think they have been exposed to someone with active TB should alert their doctors.
The National Institute of Allergy and Infectious Diseases (NIAID) funds research aimed at finding new drugs or drug combinations for the treatment of TB, as well as better ways to administer currently available drugs for prevention and treatment. For more information on these or other studies, call the AIDS Clinical Trials Information Service: 1- 800-TRIALS-A (1-800-874-2572)
NIAID, a component of the National Institutes of Health, supports research on AIDS, tuberculosis and other infectious diseases as well as allergies and immunology. NIH is an agency of the U.S. Public Health Service, U.S. Department of Health and Human Services.
Prepared by: Office of Communications National Institute of Allergy and Infectious Diseases National Institutes of Health Bethesda, MD 20892
Public Health Service U. S. Department of Health and Human Services November 1994