A Practical Guide to Tuberculosis Testing and Treatment

Understanding What Is It, How It Is Diagnosed and How It Is Treated

Electron micrograph of the Mycobacterium tuberculois bacterium. Photo credit: National Institute of Allergy and Infectious Diseases (NIAID)

Tuberculosis (TB) is a pulmonary (lung) disease that was once very common in the U.S. and remains one of the most widespread and deadly communicable diseases on the planet. The association between HIV and TB is high, with co-infection rates hitting 30% or more in many developing countries.

In the U.S., the incidence of TB among people with HIV is higher than in the general population, warranting closer surveillance among those most at risk.

What is Tuberculosis?

TB is a disease caused by the bacteria known as Mycobacterium tuberculosis (pictured). TB most often affects the lungs but can spread and infect many other parts of the body, as well.

TB infection is classified in one of two ways:

  • A latent TB infection, which is not causing symptomatic illness and is not contagious.
  • An active TB infection which is contagious and can present with such initial symptoms as cough, blood-tinged sputum, night sweats, and fever.

TB is more common in people with HIV as it is more likely to develop in those with compromised immune system (i.e., where the body is unable to develop itself). As such, it is considered an opportunistic infection and can be classified as an AIDS-defining condition when it spreads beyond the lung (or becomes an extrapulmonary TB infection).

Extrapulmonary TB can affect numerous organ systems, including the kidneys, abdomen, spine and skin, and generally develops when a person's CD4 count is below 200 cells/mL.

How is TB Spread?

TB is spread from person to person via microscopic water droplets containing the TB bacteria. When a person with active TB coughs or sneezes, infected water droplets can be aerosolized and released into the atmosphere. Exposure occurs when other people inhale these droplets, which can lead to infection.

Active TB can happen as a result of person-to-person exposure or due to a sudden reactivation of a latent infection. A person cannot get TB from shaking hands, sitting on a toilet seat, sharing dishes or utensils, or hugging.

What Are the Symptoms of Active TB?

The signs and symptoms of an active TB infection include:

  • A severe, persistent cough lasting longer than three weeks
  • A cough producing thick and/or bloody sputum
  • Chest pain and/or shortness of breath
  • Persistent weakness or fatigue
  • Weight loss and poor appetite
  • Chills and fever
  • Night sweats

How Do I Know If I Have TB?

In its earliest stages, active TB can be mistaken for other lung infections. It can often be initially diagnosed with a chest X-ray, followed by a sputum culture test that can take anywhere from 2-8 weeks to produce a positive or negative result.

A tuberculin skin test can be used in both latent and active infection. The test is performed by placing a small amount of TB protein (called purified protein derivative, or PPD) just beneath the skin on the forearm.

A reaction will typically develop in two days by which doctors are able to ascertain if you are negative or positive.

The tuberculin skin test, however, cannot distinguish as to whether you have active or latent TB infection. This can only be confirmed with a chest x-ray or sputum culture, as well as through direct visual examination of your airway using bronchoscopy.

Faster TB testing assays are also now available, including the Xpert MTB/RIF test which can both detect the infection as well as any drug resistance the virus may have to rifampicin (a first-line TB drug).

Overview of TB Treatment

In an active TB infection, treatment is in the form of combination drug therapies which are prescribed for two months initially and then a maintenance dose for four months. Treatment must be taken with high levels of adherence and to completion even if the symptoms have disappeared. Failure to do so can result in relapse, as well as the development of resistant to the drugs used to fight TB.

Latent TB is also treated when infection is confirmed to prevent the development of active infection. Dosages and medication differ from active TB treatment with the duration of therapy ranging from 6 months to a year.

The drugs used to treat active and latent TB include:

  • Isoniazid (INH)
  • Rifampin (RM)
  • Pyrazinamide (PZA)
  • Ethambutol (EMB)
  • Pyridoxine (Vitamin B6) - used to replace Vitamin B6 lost as a result of taking TB drugs

Can HIV and TB Medications Be Taken At the Same Time?

HIV and TB medications can generally be taken at the same time. While it had one time been common practice to initiate TB treatment first, it was shown that the practice increased the risk of death significantly in severely ill HIV patients.

Persons with extremely low CD4 counts, however, run the risk of a complication called immune reconstitution inflammatory syndrome (IRIS). The condition, in which the body essentially "over-activates" its immune response, results in an inflammatory response that can sometimes be severe

IRIS occurs most frequently in newly treated patients, in those with very low pre-treatment CD4 counts (under 50-100 cells/mL), or in those who have been recently or currently treated for an opportunistic infection like tuberculosis. 

Sources:

Centers for Disease Control and Prevention. "Tuberculosis (TB)."  Atlanta, Georgia; Division of Tuberculosis Elimination; accessed February 11, 2016.

Jacobson, M. “Clinical Implications of Immune Reconstitution in AIDS.” HIV InSite Knowledge Base [textbook online]. UCSF Center for HIV Information, San Francisco, 2006.

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