Tuberculosis

Tuberculosis (TB) is a disease caused by the bacteria Mycobacterium tuberculosis. It most commonly affects the lungs, although it can affect other parts of the body. Medications are available to treat TB and must be taken as prescribed by your provider. Depending on the medication(s) prescribed, the duration can be from four months to nine months or more.

Worldwide, TB remains a leading cause of death. In the United States, TB is on the decline. In 2016, more than 9200 new TB cases were reported in the United States, with cases reported from every state. This is the lowest number of national cases since TB became a reportable disease in the 1950s.

TB can be fatal if not recognized and treated. It also can spread from person to person to infect others. However, TB is treatable and preventable. Identifying and treating those who are infected but who have not yet become ill with active TB can prevent the disease and thus eliminate the spread of TB in the community.

HOW DOES TUBERCULOSIS OCCUR? 

— The tuberculosis (TB) bacteria are spread through the air from a person who is ill with active TB that involves the lungs or airways. In these infectious individuals, bacteria are contained in small airborne droplets created by coughing or sneezing. Anyone who inhales these droplets is called a “contact.” A contact can be someone who spends a lot of time with the person who has infectious TB, such as a family member, friend, or coworker.

The contact person does not usually develop active TB immediately. In some cases, the person’s immune system is able to remove the bacteria and he/she does not develop the disease. In other cases, the person develops an immune response that controls the bacteria by containing it inside the body. This causes the bacteria to become “latent” (dormant, or asleep). The person does not develop active TB or become ill at this time but is said to have latent TB infection (LTBI). Up to one-third of the world’s population is infected with LTBI.

Latent TB — During this latent stage of TB, also called TB infection, the person is well and cannot spread the infection to others. If the person is treated at this stage, active TB can usually be prevented. Treatment is recommended for TB-infected individuals who are at increased risk for the development of active TB.

Active TB — Active TB may develop if latent infection is not fully treated. This is called reactivation TB, and it occurs in 5 to 10 percent of people with latent infection at a later time in their lives.

Reactivation TB may occur if the individual’s immune system becomes weakened and is no longer able to contain the latent bacteria. The bacteria then become active; they overwhelm the immune process and make the person sick with TB. This also is called TB disease.

The greatest risk for developing reactivation TB disease is within the first two years following the initial infection as a contact to a person with infectious TB. Reactivation can also occur more readily in people with HIV, diabetes mellitus, malnutrition, or those who take medications that weaken the immune system, such as medications for rheumatoid arthritis, steroids, or cancer chemotherapy. It can also occur with aging and weakening of the immune system. Reactivation may also occur for other unknown reasons.

HOW IS LATENT TUBERCULOSIS DIAGNOSED? 

— Latent tuberculosis (TB) infection (LTBI) can be diagnosed with a skin test or with a blood test, followed by a clinical evaluation and imaging (usually a chest X-ray) to make sure the tuberculosis is not active and causing disease. These tests recognize the immune system’s prior exposure and sensitization to the TB bacteria and result in a positive test after TB infection has occurred.

Skin testing — The TB skin test is known as the tuberculin skin test (sometimes also called a purified protein derivative test [PPD]) and is one method of detecting TB infection. In a person who is newly infected, the skin test usually becomes positive within 4 to 10 weeks after exposure to the person who is ill with TB.

TB skin tests are performed by injecting a small amount of PPD solution just beneath the surface of the skin, usually on the forearm. This solution contains an inactivated portion of the TB bacteria. Most individuals previously infected with TB develop a skin reaction (red or swollen) at this site.

Some reasons for skin testing — Tuberculin skin tests generally are performed for persons who are at risk of having TB infection:

●If the person is a healthcare or laboratory worker who may be a new employee to a healthcare facility or have contact with patients infected with TB.

●If the person knows he or she was exposed to someone with active TB. If the first test is negative, a second test usually will be performed 8 to 10 weeks later.

●If the person requires a medication that may weaken the immune system, such as steroids or medications for rheumatoid arthritis.

●If the person has HIV infection.

Interpreting the results — The skin test must be examined 48 to 72 hours after the PPD solution is injected under the skin. The skin is examined to determine if there is swelling (a reaction) at the injection site. The area may also be reddened, but redness should not be measured.

A trained healthcare provider (not the patient or a family member) interprets the test as positive or negative based on the size of the reaction and criteria for what size of reaction is considered positive in certain patient groups. Anyone who has a reaction larger than 15 mm is considered to have a positive test, and some people with a reaction that is 5 mm (eg, HIV, close contact to an active TB case) or 10 mm (eg, recent immigrant from a region with a high rate of TB) are considered to have a positive test if they are at higher risk for developing TB.

What does a positive TB skin test mean? 

— The TB skin test indicates that TB bacteria are in the body. It cannot determine if a person has active TB disease or LTBI; this requires further testing, usually a chest X-ray and a clinical examination. People who have active infectious TB usually have symptoms, such as a cough (usually persisting for several weeks), fevers, night sweats, and/or unexplained weight loss.

Skin testing after a positive test in the past 

— Anyone who has demonstrated a positive reaction to the TB skin test in the past usually will have a positive reaction in the future. Even after taking medication to treat TB, the reaction to the skin test will remain positive. Therefore, anyone who has a positive skin test does not need to have skin testing again. Repeat testing can rarely cause a large and painful skin reaction at the injection site and should be avoided.

BCG vaccine — A TB vaccine called Bacillus Calmette-Guérin (BCG) is given in many countries to prevent infection with TB. It usually is given to infants, although it may be given again at other times. BCG offers protection against TB in young children but typically does not offer continuing protection. BCG is not routinely used to prevent TB in the United States.

This vaccine may or may not cause a positive skin test. In the United States, a positive reaction to a TB skin test is interpreted as positive, regardless of prior BCG vaccination. Previous BCG vaccination should NOT stop a person from obtaining a TB skin test unless the person had a positive TB skin test reaction in the past.

Two-step skin testing — In some people, the TB skin test is falsely negative because the immune system’s response to TB has weakened over time. This may occur in people who were exposed to TB many years before. If a first skin test is negative, a second skin test may be done one to two weeks later. Performing the first test may “boost” the immune system, allowing it to react on the repeat test if the person was previously exposed to TB.

If the person has two negative tests, this is considered a true negative. If the second test is positive, further testing will be done to determine if the person has active TB disease or LTBI.

Two-step testing establishes a baseline in people who will need skin testing at regular intervals in the future (eg, healthcare workers, employees and residents of institutions such as prisons or nursing homes).

Blood tests for TB — Blood tests, known as interferon-gamma release assays (IGRAs), are available as another option for testing to identify TB infection. The blood test may be offered instead of, or in addition to, the TB skin test. Blood tests may simplify TB testing because they do not require the person to make a return trip to read the test reaction. In addition, blood test results for TB infection are not affected by prior immunization with BCG vaccine or by prior infection with harmless bacteria from the environment that might affect the TB skin test.

Further testing — If the TB skin test or blood test is positive, a healthcare provider will ask some specific questions, perform a physical examination, and obtain a chest X-ray to determine if person has active TB, either currently or in the past. In some cases, the person will be referred to a TB specialist for this evaluation.

If these tests indicate that the person has active TB rather than LTBI, the treatment regimen is different than that of someone with LTBI.

TREATMENT OF LATENT TUBERCULOSIS

Treatment approach — Latent tuberculosis (TB) infection (LTBI) is treated with one or more medications to kill the latent bacteria. Treating LTBI greatly reduces the risk of the infection progressing to active TB later in life (ie, it is given to prevent reactivation TB disease). Prior to starting treatment, it’s important to review all current medications with your health care provider in order to avoid any possible medication interactions.

While undergoing treatment, it is important to avoid drinking alcohol and taking acetaminophen (Tylenol). Both of these substances can make the liver work harder, potentially increasing the risk of liver injury from the medications.

There are several different regimens available for treating LTBI:

●Rifampin daily for four months

●Isoniazid plus rifampin daily for three months

●Isoniazid plus rifapentine weekly for three months

●Isoniazid daily for six or nine months

The best regimen depends on potential medication interactions, concerns about side effects, and how likely the person is to take all of the medication. It’s important to finish the entire course of treatment.

If there are concerns that a person may not be able to reliably take their medication on schedule and/or report any side effects, the health care provider might suggest “directly observed therapy”. In other cases, the person can take his or her medication at home without direct observation.

Monitoring during treatment — People who are being treated for LTBI must be monitored by a healthcare provider at least once per month to monitor for any signs of medication toxicity, such as liver injury. Minority women in the postpartum period may be at higher risk for side effects. Signs of liver injury may include unexplained tiredness, loss of appetite, nausea, vomiting, dark-colored urine, jaundice (yellowing of the skin or the white portion of the eye), fatigue, abdominal pain, or, rarely, unexplained bruises. Anyone who experiences one or more of these problems while taking any of these medications should stop their medication immediately and notify their healthcare provider.

In certain special cases, monthly monitoring may also include blood tests to monitor the function of the liver or blood counts.

ACTIVE TUBERCULOSIS — Active tuberculosis (TB) disease occurs when the TB bacteria become “active”; they overwhelm the immune system and cause a person to become ill. This usually occurs in the lung, although TB can affect any part of the body, including the lymph nodes, brain, kidneys, or bones.

If there is evidence on a chest X-ray or other signs that active pulmonary (lungs) TB is present, sputum cultures will be performed to culture (grow) the bacteria in the laboratory. This usually involves coughing up a “deep” specimen of phlegm from the chest. The phlegm is then sent to a laboratory and cultured to determine if TB bacteria are present. Other tests, such as a bronchoscopy or biopsy, may also be needed. A tissue biopsy may be performed to obtain specimens for culture if TB is suspected in other organs (such as lymph nodes or kidney).

While waiting for the results of the culture (some laboratory results are positive within a day or two, but it may take as long as two months for the bacteria to grow in the laboratory), treatment with several (usually four) TB drugs may be recommended. It is important to use more than one medicine and to take the medicines exactly as prescribed to reduce the risk of the bacteria becoming resistant to one (or more) of the medicines.

Infection caused by a strain of TB that has become resistant to standard TB drugs is more difficult to treat and may require four to six medications and a longer duration of treatment.

TUBERCULOSIS AND PUBLIC HEALTH — Tuberculosis (TB) is a disease that can easily be spread through the air by anyone with active disease. As a result, laws in the United States require that anyone with active TB be reported to the health department. Health department staff will work with the patient’s healthcare provider and the patient to make sure that a safe and effective treatment regimen is completed.

Directly observed therapy (DOT) is a program used by public health departments to ensure that a patient safely takes his or her medication exactly as prescribed. Since there is daily interaction with a healthcare worker where symptoms and signs of an adverse reaction to the medication can be reviewed, DOT also minimizes the risk of serious side effects. With this program, a health worker watches a person swallow the TB medication every day. DOT may help to improve cure rates.

The health department can also help to identify people who have been in contact with a person with active TB. Contacts are advised to have TB testing and treatment if necessary.

Public health programs for TB are essential for several reasons:

●To reduce the number of new cases of TB (by identifying and treating people with LTBI in order to prevent disease from developing) and therefore

●To limit spread of the disease in the community (by monitoring and assuring safe, complete treatment of people with active TB).

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