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The facts on TB - and why you should know them

Having a positive reaction to a Mantoux test requires further investigation

Do you remember the patient from last year? The one complaining of fatigue and cough for several weeks? The one you gloved up for but skipped the mask because he didn’t look that sick? The one that shared his tuberculosis with you? Don’t recall?

You do recall that last week your annual tuberculin skin test turned positive for the first time. The tuberculin skin test or Mantoux test uses proteins extracted from Mycobacterium tuberculosis, the rod shaped bacteria causing TB.

This purified protein derivative (PPD) is injected intradermally between the skin layers and then inspected for a reaction in 48 to 72 hours1. A red, raised wheal at the site of the injection is a positive reaction.

At the time you were contaminated with the TB bacteria, your immune system mounted an initial attack that formed a wall around the tuberculosis bacteria called a tubercle thus preventing further bacterial dissemination. Weeks or months later when you received your annual PPD containing proteins from the TB bacteria, your immune system remembered the previous exposure and responded with a positive reaction to your annual PPD, confirming that you have tuberculosis.

With a positive PPD test, you will need a chest x-ray to look for pulmonary signs of an active TB infection. If you are active, you may also exhibit the following signs and symptoms:

  • A persistent cough
  • Constant fatigue
  • Weight loss (active TB consumes you body resources, thus ‘consumption’ is an old term for TB)
  • Loss of appetite
  • Fever
  • Coughing up blood
  • Night sweats

If your PPD is positive, but your chest x-ray is negative, and you are not exhibiting these signs and symptoms, you have latent TB2.

Latent TB
Latent tuberculosis is when you are infected with the TB bacteria but your immune system prevents the bacteria from increasing their numbers and activity. You are infected with TB but are not infectious and cannot share the disease with others, yet.

You now have the option of taking anti-tuberculosis medication to rid your body of TB and prevent future spread to the lungs and other organs. According to the CDC, healthcare workers are a high priority population for treatment of latent TB. There are four treatment options using one or more drugs for 3 to 9 months. For example, Isoniazid (INH) is taken for six to nine months for latent tuberculosis3. There is a risk of side effects from the medication, but overall the benefit outweighs the risk.

Your PPD will remain positive on future tests because your immune system will remember your infection with TB. Do not repeat a PPD once you have a positive reaction especially if it was extensive as this may cause a destructive local reaction and damage to your skin and subcutaneous tissue4.

Active TB
But what if you don’t take the medication or don’t have access to anti-TB treatment as in many underdeveloped countries?

You may be okay for a while but at any point your immune system weakens, Mycobacterium tuberculosis could expand its territory. This is why individuals with less responsive immune systems are more prone to develop active TB. These include patients with HIV, advanced age, malnutrition, chronic disease, or on long term medications that suppress the immune system such as certain cancer therapies or anti-inflammatory drugs like steroids5.

With a positive PPD and symptoms of active TB, you may need another CXR to look for changes. You will be required to produce morning sputum specimens that will be stained and cultured for the TB bacteria.

An acid fast stain is used to dye the tuberculosis bacteria. They appear as red rods under the microscope confirming that you are infectious and can spread TB. If you are sick enough to require hospitalization, you will be placed in a negative pressure isolation room that will exchange the room air several times an hour to prevent contaminating the facility. The hospital staff will gown, glove and wear masks when caring for you.

If you are infectious but well enough to be at home, you will receive instructions on limiting exposure to others by limiting travel, having your own room that can be aired out frequently and covering your mouth with tissue when you cough, sneeze or laugh.

Once the mycobacterium starts to grow in the culture medium it can be tested for drug sensitivities. At times the bacteria may take weeks to grow a visible colony. Determining what drugs will effectively kill your personal tuberculosis bacteria is especially important with the increasing incidence of multi-drug resistant TB.

And what do you do while the cultures are growing and you are waiting for your sputum stains to turn negative? You will receive a standard four drug therapy consisting of first-line TB medications including isoniazide, rifampin or rifapentine, ethambutol and pyrazinamide. If resistance to any of these first-line therapies show up on your culture, alternative drugs are available6.

Tuberculosis is on the increase worldwide including our country with 500,000 new cases every year. And more and more Mycobacterium tuberculosis is becoming resistant to standard treatment. You work in a high risk environment which includes exposure to your patient’s infectious diseases. The TB bacterium is transmitted through the air from lung to lung. When your patient coughs, paint a mind-picture of the millions of bacteria that are expelled into the air between the two of you; without a mask you will inhale that cloud of organisms. If your patient has a cough or a known pulmonary infection, put a mask on yourself and slip one on your patient. It is easier to prevent a disease than to have the disease.


  1. American Thoracic Society and CDC. Diagnostic standards and classification of tuberculosis in adults and children . Am J Respir Crit Care Med 2000; 161.
  2. CDC: Fact Sheet: The Difference Between Latent TB Infection and TB Disease. Department of Health and Human Sevrices. Retrieved February 10, 2013 from
  3. CDC: Fact Sheet: Treatment Options for Latent Tuberculosis Infections. Department of Health and Human Sevrices. Retrieved February 10, 2013 from
  4. CDC: Fact Sheet: Tuberculin Skin Testing. Department of Health and Human Sevrices. Retrieved February 10, 2013 from
  5. CDC: Tuberculosis Infection Control and Prevention. Department of Health and Human Sevrices. Retrieved February 15, 2013 from
  6. CDC: Fact Sheet: Treatment of Drug-Susceptible Tuberculosis Diseases in Person Not Infected with HIV. Department of Health and Human Sevrices. Retrieved February 20, 2013 from
Jim Upchurch, MD, MA, NREMT, has focused on emergency medicine and EMS while providing the full spectrum of care required in a rural/frontier environment. He provides medical direction for BLS and ALS EMS systems, including critical care interfacility transport.