MYCOBACTERIUM TUBERCULOSIS (TB)

Description

Tuberculosis (TB) is a disease caused by a rod-shaped bacteria called Mycobacterium tuberculosis. The bacteria usually attacks the lungs. Extra-pulmonary TB occurs less commonly than pulmonary TB. It can attack any part of the body such as the muscles, kidney, spine, and brain. Extra-pulmonary occurs more frequently in patients infected with HIV, but pulmonary tuberculosis remains the most common type of tuberculosis in this group world wide. However, only pulmonary TB is spread from person-to-person. If not treated properly, TB can be fatal. TB disease was once the leading cause of death in the United States. Worldwide, each year about 2 million people die from the disease.

There are 3 distinct phases of TB; exposure, infection and disease.

To become infected, a person would have to be exposed for a relatively long time in a closed environment where the air is contaminated by a person with untreated TB who is coughing and who had multiple M. tuberculosis organisms in secrestion from the lungs.

Following an exposure to a person with active pulmonary TB disease, infection may go undetected. A PPD (purified protein derivative), skin test will detect if a person has had an exposure to the disease. PPD skin test sensitivity appears within 2-10 weeks. Because TB was so much more prevalent years ago, many older persons will have been exposed to the germ and may have a positive PPD. It is important to remember that not everyone exposed to the TB bacteria will develop an active infection and become sick. People who have a positive PPD but are not sick have what is called latent TB exposure (see chart below). People with an exposure to TB, or latent TB infection can take medicine so that they will not go on to develop active TB disease in the future.

People with signs and symptoms of active TB disease can be treated and cured if they seek medical help. These symptoms include fatigue, fever, night sweats, weight loss, cough, chest pain, hemoptysis and hoarseness.

A Person with Latent TB Infection

• Has no symptoms
• Does not feel sick
• Cannot spread TB to others
• Usually has a positive skin test
• Has a normal chest x-ray and sputum test

Starting in the 1940s, scientists discovered the first of several medicines now used to treat TB. As a result, TB slowly began to decrease in the United States. But in the 1970s and early 1980s, the country let its guard down and TB control efforts were neglected. As a result, between 1985 and 1992, the number of TB cases increased. However, with increased funding and attention to the TB problem, we have had a steady decline in the number of persons with TB since 1992. But TB is still a problem with more than 14,000 cases reported in 2003 in the United States. One of the most serious problems deals with bacterial drug resistance due to poor drug taking compliance. Directly observed therapy has been shown to be highly effective and is recommended for the treatment of TB disease in the United States.

Where are they found?

Primarily in humans, rarely in primates. In some areas, in diseased cattle, badgers, swine and other mammals.

How do we get infections?

TB is spread through the air from one person to another. The bacteria are put into the air when a person with active TB disease of the lungs or throat coughs, sneezes or sings. People nearby may breathe in these bacteria and become infected.

When a person breathes in TB bacteria, the bacteria can settle in the lungs and begin to grow. From there, they can move through the blood to other parts of the body, such as the kidney, spine, and brain.

TB in the lungs or throat can be infectious. This means that the bacteria can be spread to other people. TB in other parts of the body, such as the kidney or spine, is usually not infectious.

People with active TB disease are most likely to spread it to people they spend time with every day. This includes family members, friends, and coworkers.

Bovine tuberculosis results from exposure to infected cattle usually by ingestion of unpasteurized milk or dairy products, and sometimes by airborne spread to farmers and animal handlers.

Incubation period

A significant skin test reaction, indicating that infection has occurred approximately 2-10 weeks after exposure. Subsequent risk of TB disease is greatest within the first year or two after infection. However latent infection may persist for a lifetime if left untreated. HIV disease increases the risk greatly and shortens the interval for the development of active TB disease. The risk of developing disease is highest in children under the age of 3, lowest in later childhood, and high again in adolescents, young adults, the very old and the immunosuppressed.

Treatment

The most common medicines used to cure TB are:

• isoniazid (INH)
• rifampin (RIF)
• ethambutol
• pyrazinamide

After taking medicine for about 2 or 3 weeks, patients may no longer be able to spread TB bacteria to others. Patients will get well only if they take their medicine exactly as a doctor or nurse outlines. Patients also need to keep their clinic appointments. Patients may need additional chest x-rays or a test of the phlegm coughed up to show whether the medicine is working.

Prevention

Proper handwashing and good housekeeping practices should be observed as a general rule.

No special precautions are needed for handling dishes, laundry, bedding or personal effects. TB is spread via the air, not by fomites. ( any inanimate object or substance. other than food, that harbors or carries infectious organisms)

Isolation in a hospital setting is generally required for pulmonary TB. Patients will be placed in a private room with negative air pressure. Personal respiratory protective devices capable of filtering submicron particles will be worn by medical staff. With prompt drug therapy negative chest e-rays and sputum smears can be achieved within 4 to 8 weeks.

Educate the public on modes of spread and the patient in the use of a tissue when coughing or sneezing to help prevent the transmission of germs via the air.

Reduce or eliminate, where possible, conditions of over crowding.

Educate the public on methods of control and the importance of early diagnosis, preventive therapy and compliance to taking all medications as prescribed.