In the United States, the incidence of TB began to decline around 1900, due to improved living conditions.  However, TB cases have increased since 1985, most likely due to the increase in HIV.  Foreign-born persons also account for a steadily-growing proportion of TB cases in the US.  The emergence of drug-resistant TB organisms threatens to make this disease once again incurable.

All cases of TB are passed from person to person via airborne droplets.  When someone with TB infection coughs, sneezes, or even talks, tiny droplets of saliva or mucus are expelled into the air; exposure to TB occurs by sharing common air with someone who is infectious.

When inhaled, the droplets become deposited in the lung.  If the organism causes clinically detectable disease, you have TB. People who have inhaled the TB organism but who have no symptoms are still infected.  However, only about 10% of the people infected with Mycobacterium tuberculosis actually develop tuberculosis disease.

Initial TB infection in the lung is called primary pulmonary tuberculosis.  Most initial infections have no symptoms other than just a fever, and dry cough; most people may think they just “have a cold.”  Primary pulmonary TB frequently goes away by itself, but in 50 to 60% of cases the disease can just become dormant, and eventually return.

In a small percentage of the population with weakened immune systems, the initial TB infection can spread from the lung through the bloodstream, to other parts of the body.  15% of people can develop TB in an organ other than the lungs; these other sites include the spine, urinary tract, lining of the gastrointestinal tract, or brain.

Return of a dormant TB infection - called “reactivation” of TB - occurs in the upper part of the lungs.  The symptoms are cough, with a progressive increase in mucus production that can be bloody; fever; loss of appetite; fatigue; and night sweats.  You may not even notice any symptoms of illness until the disease is quite advanced and, even then, you might think the symptoms are because of something else, like the “flu.”

The Mantoux test is the only currently available test for diagnosing a TB infection, in the absence of active disease.  A doctor injects 5 units of purified protein derivative (PPD) into your skin, usually the inside of your forearm.  The doctor then reads the test within 48 to 72 hours after the injection.  The injection site may or may not be reddened, but redness alone does not mean a positive response.  The doctor will measure the amount of induration or “firmness” of the skin reaction at the injection site.  Immigrants are considered to have a positive Mantoux test (a “positive PPD”) if the area of induration is greater than 10 millimeters.

If your Mantoux test is positive, the next step is to obtain a chest x-ray to determine if active disease is present.  Your doctor will look for the presence of cavitary lesions or other signs of infection in your lungs.

If you are found to have active TB, doctors will prescribe several special medications that you must take for 6 to 9 months.  Multiple drugs are used to reduce the likelihood of the organisms in your body becoming resistant.  Treatment takes that long because the organisms grow very slowly and, unfortunately, also die very slowly.  If doctors doubt that you are taking your medicine, they may have you come to the office for your medication dosages.

Even if you do not have active TB, if your reaction to the Mantoux test was significant you will be required to undergo a course of treatment with Isoniazid.  This treatment is intended to kill the walled-up organisms that may not be doing any damage right now, but may break out years from now and become active.

An important aspect of tuberculosis treatment is public health.  You must take your medications as directed, even if you are feeling well.  The most common cause of treatment failure is not complying with the prescribed medical regimen.  This can result in the organisms in your body becoming resistant to our drugs to treat TB - which can have very serious consequences if you become actively infected with the TB, since there will be no drugs able to kill the organism.  Doctors will also very likely contact your relatives and friends, since they may need to undergo skin tests and chest x-rays to determine whether they may also need treatment.