Tuberculosis—How Do You Get It?

Let us suppose for discussion purposes that a middle-aged lady comes to the physician’s office for her annual physical exam.  She has been feeling well and essentially has no physical complaints.  Her physical exam is within normal limits.  Because she has been doing volunteer work at the homless center the physician recommends that she have a T.B. skin test.  Either a TB tine test or a PPD (Purified protein derivative) skin test is administered.  In both rest a small amount of TB protein is injected into the subcutaneous layer of the skin.  In order to read it, the patient must return in 72 hours.  It cannot be read reliably prior to that time duration.  The physician evaluates the skin at the injection site.  He is not just looking for redness alone, but for an elevating reaction that feels sort of like a coin in size of 1 cm or larger under the skin. If it is there, the presumption is that the patient has inhaled some Tuberculosis since her last negative skin test.  The physician may order a gamma interferon assay blood test because it is much more accurate and can help sort out a false-positive skin test.  Now, it’s time to really intensify the history review.  Does she have an unusual cough, and if so, has there been any blood in her sputum?  Has she had fevers, felt hot at unusual times, or had nightsweat? Has she lost any weight without intending to do so? Has she felt fatigued, had difficulty breathing, had chest pain or wheezing? This is very important information. Finally, the doctor orders a chest x-ray and looks for any evidence of active disease.

 At this point there are three possibilities. The patient may have had a false-positive skin test. The gamma interferon assay blood test would reiterate this fact. The second possibility is that the patient inhaled T.B. germs which have attacked her body defenses, and forced into a quiet and dormant form for decades waiting for the chance to overwhelm the body defenses. This is called latent infection. The germs can persist in their dormant form for decades waiting for the chance to overwhelm the body defenses. The patient could have active disease, as evidenced by an abnormal chest x-ray and sputum positive for germs on microscopic exam or by culturing the sputum for several weeks. Now the physician must weigh all the facts at hand. Does the patient have latent or active disease? If all findings suggest dormant disease, the patient is placed on isoniazid (INH) antibiotics for one year. The patient must come in monthly for blood tests to make sure her liver is not being adversely affected. If she has active infection she is placed on four drug therapy including INH, rifampin, pyrazinamide, and ethambutol. This is continued for at least two months until the cultures come back. She is usually non-infectious after two months of this therapy, and medications can be deleted or added according to the culture results. The treatment should bring resolution of the infection in six to nine months but sometimes as long as 2 years. This latter situation would, by law, require a report to the local Health Department so they could test all contacts and ensure resolution of the spread of disease.

The problem with T.B. therapy is that patients, world-wide, do not take their medicines as prescribed. Sometimes they don’t feel bad anymore and just stop taking them. In some places the drugs are expensive and are stopped for that reason. Whatever the cases, if the drugs are stopped too soon, the bacteria can rebound with a vengeance. It can become resistant to drugs, and in the extreme case, they become resistant to all the drugs, usually with fatal consequences. The drug resistant bacteria may be passed along to others. The infection is spread by the micro-droplets in a cough or sneeze. Each droplet can contain enormous number of the bacteria. It is usually carried into lungs. Usually the lower part of the lower lobe is first infected and then it moves to the lower part of the upper lobe. It sets up in the air sacs called alveoli and enters cells called macrophages. The body sends many types of defensive cells to combat it, and these may bring about a walling off of the infection into its dormant phase. If this doesn’t happen the infection can grow into abscesses in the lung or spread to other organs by way of the bloodstream.

The developed countries of the world become pretty comfortable with tuberculosis during the 80’s and 90’s. Gwinnett County, Georgia in the last 5 years  has dramatically increased its T.B. population. It was generally thought of as a disease of developing countries, you know, “over there.” No new drugs came on the market and the resistance problem began to grow. Now, with the developing of “globalization”, anything which happens in any part of the world is a concern to us all. Travel into and out of endemic areas is increasing in frequency. A lot of infection is associated with the arrival of immigrant populations. The other phenomenon is the development of H.I.V., in which infection can be more severe, more drug-resistant, and require more intensive plans of treatment.

Face it: Tuberculosis is out there. Eight million people world-wide become sick each year with infection.  Fourteen million have active disease at any given time. Over a million die with it every year. Cases in developed countries are increasing due to H.I.V., immunosuppressant drugs, and drug abuse. Many things increase the chances of infection like silicosis, cigarette smoking, and nutritional deficiencies such as inadequate vitamins B12 or D. It is seen with increased frequency with the homeless, in infants and the elderly, or with people who live in crowded unsanitary conditions. Remember our patient who volunteered at the homeless center: The more you are around people with the disease, the more likely you are to become infected.

A lot of research is going into vaccines, possibly including one with intranasal dosing. There are new antibiotics in trials right now for multi-resistant strains. Research is being directed toward increasingly accurate and inexpensive blood tests for dormant or active disease. International efforts are underway to bring effective treatment to the ill in developing countries. We can increase our personal awareness and knowledge about this infection. We can make skin or blood testing a part of regular physical exams. We can support causes and organizations whose goal it is to eradicate tuberculosis from the planet. We can practice the courtesies of hygiene to prevent the spread of infectious diseases to other people. We can identify segments of our population most in need of infection surveillance. By research, political commitment, and dedication to facing this human condition, we can move toward the day that we are making progress in the prevention and treatment of this horrible disease.