LATENT TUBERCULOSIS

Apr 13, 2022 Irene Lamunu Leading Health 0

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The Uganda Marathon 2022Marathon banner read, “Did you know that everyday 30 Ugandans die of Tuberculosis (TB)?” On a social media platform, after someone asked why it seemed like the cases of TB in Uganda were rising, another respondent agreed to mention that her healthy brother and uncle had both been recently diagnosed with TB. Yet another chimed in saying she was at a funeral of someone who had recently complained of
chest pain and was now dead and they feared it was TB (very unlikely,
TB does not kill within a week of onset). By the end of the discussion,
there was fear in the group and the input of doctors was requested. This
article is a summary of the medical input that the group received.

How do I know that I am suffering from TB?

World over, one must be tested for TB if they have had a cough for more
than two weeks. Symptoms that increase the chance that the cough
could be due to TB are; evening fevers, drenching sweats at night and unintended weight loss. When you present these symptoms, a sputum sample will be requested and tested for TB. While there are many tests for TB these days, the gold standard (most reliable test) remains the sputum culture – sputum is placed in a medium that the TB bacteria thrives in and any live TB in the sputum will multiply and grow in it. This requires waiting
for at least 6 weeks for the results. Today, the most used and fastest test
is the GeneXpert. It works by rapidly amplifying any TB bacterium that
is present in a sputum sample. It gives results within a few minutes or hours.

Who gets ill with TB?

Most times, TB requires a weakened immune system to multiple and
make one sick. That is why most times it is associated with HIV. People on treatment for cancer are also at an increased risk for TB. Sometimes, we make ourselves prone to TB by using steroids e.g. prednisone and dexamethasone, without proper medical supervision or prescription.

Latent TB Infection

Latent TB infection (LTBI) is really a sleeping TB infection. This is when
a person with an intact immune system is exposed to TB bacteria, most commonly by breathing in particles with the bacteria from the cough or mucus of someone with an active infection. When the infection starts in the lungs, the body quickly reacts to it and creates a protective wall around the bacteria. Unfortunately, because the body cannot kill the bacteria, it remains alive but not strong enough to breach the wall and the body’s immune system continually reinforces around it. Most of us have latent LTBI; often, we were exposed several years ago and because of the intact immunity, we aren’t sick. It is estimated that over 30% of the world’s
population globally carries LTBI. The estimate is as high as 49% in Uganda.
Globally, among health care workers, it ranges from 62% to 84% because of
frequent exposure to people with active TB infection. Most TB cases arise from people with LTBI within a period of 2–5 years following primary infection (first infection with the TB bacteria). Between 5 and 15, out of every 100 people with LTBI progress to active TB .

Testing for latent TB infection

While there is a skin test and blood test, the Mantoux tuberculin skin test
is highly recommended because it is available world over, easy to perform,
inexpensive, and works just as well as the more expensive blood test. The TB skin test is performed by injecting a small amount of fluid (called tuberculin) into the skin on the lower part of the arm. A person given the tuberculin skin test must return within 48 to 72 hours to have a trained health care worker look for a reaction on the arm. The result depends on the size of the raised, hard area or swelling. Positive skin test: This means the person’s body was infected with TB bacteria. Note though that the test may be positive if one received the TB vaccine in the last 15 years. It may be positive also if one is infected with other forms of mycobacterium. A negative skin test means the person’s body did not react to the test, and latent TB infection or TB disease is not likely. People with low immunity may have a negative test even when they have an active TB infection.
To treat or not to treat latent TB infection? In countries with very low levels of TB, those found with LTBI are put on treatment. In high prevalence countries (most countries in Africa and Asia), there is a cost-effectiveness issue at the policy level. Almost half of the population in these countries has LTBI, treated people will likely get re-infected, and yet the risk of progression to active TB is low. Also, because treatment of LTBI takes
months, many people will not adhere to the medication, resulting in drugresistant strains of TB. It is, therefore, cheaper and safer for the country not to treat those with LTBI and focus on the diagnosis and treatment of active TB. It is the reason most of these countries and the WHO guidelines do not recommend the treatment of latent TB. One can, however, ask and pay for LTBI in a private setting but if you do so, remember that you have the responsibility to take the treatment and finish it or risk creating a resistant strain of TB which is more life-threatening than the current LTBI that you and most of us have.

DR. MIRIAM LAKER-OKETTA

She has advanced training in Epidemology and Biostatistcs. Her current research focus is HIVassociated mailgancies, specifically Kaposi’s sarcoma and cervical cancer epidemiology, early detection, diagnosis and treatment. She is also cofounder of the Hub for African Women in Science (AWISH)

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