Tuberculosis: Understanding its Testing Methods and Treatments - By Dr Markandaiya Acharya

Tuberculosis (TB) is a contagious bacterial infection that predominantly affects the lungs but can potentially affect other organs. The bacteria Mycobacterium tuberculosis causes it, and it spreads through the air when an infected person coughs, sneezes, or talks. In this post, we will look at the various tuberculosis therapies available, as well as the skin and Montaux tests used for diagnosis and the TB vaccination for prophylaxis.

Introduction

Tuberculosis (TB) is a contagious bacterial infection that predominantly affects the lungs but can potentially affect other organs. The bacteria Mycobacterium tuberculosis causes it, and it spreads through the air when an infected person coughs, sneezes, or talks. In this post, we will look at the various tuberculosis therapies available, as well as the skin and Montaux tests used for diagnosis and the TB vaccination for prophylaxis.

(Tuberculosis public health campaign in Ireland, 1905)

Understanding Tuberculosis

What is Tuberculosis?

Tuberculosis (TB) is an infectious disease caused by the bacteria Mycobacterium tuberculosis. It primarily affects the lungs, although it can also damage the kidneys, spine, and brain. TB spreads through the air when an infected person exhales respiratory droplets that others around can inhale.

(Robert Koch discovered the tuberculosis bacillus.)

Causes and Transmission

Mycobacterium tuberculosis is the microorganism that causes tuberculosis. The bacteria are released into the air when an infected person coughs, sneezes, or speaks. People in close proximity to the bacteria may breath them and become ill. It is vital to highlight that tuberculosis is not easily spread and usually necessitates lengthy and close contact with an infected person.

Symptoms and Diagnosis

Tuberculosis symptoms include 

• prolonged coughing, 
• chest pain, 
• weight loss, 
• exhaustion, 
• fever, and 
• night sweats. 

These symptoms, however, can vary depending on the place of infection within the body. 

TB can be diagnosed using a variety of techniques, including 

(An anteroposterior X-ray of a patient diagnosed with advanced bilateral pulmonary tuberculosis. This AP X-ray of the chest reveals the presence of bilateral pulmonary infiltrate (white triangles), and „caving formation“ (black arrows) present in the right apical region. The diagnosis is far-advanced tuberculosis.)

• imaging investigations (like XRAYS & MRI), 
• sputum testing, and 
• tuberculin skin tests.

Treatments for Tuberculosis

Tuberculosis can be treated using a mix of antibiotics to guarantee that the germs are eradicated completely. 

The treatment is usually divided into two stages: 

1. the initial phase and 
2. the continuation phase. 

Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol are popular first-line medications. 

If the infection is drug-resistant, second-line medications may be required in some circumstances.

Skin Test for Tuberculosis

What is the Skin Test?

The Mantoux tuberculin skin test (TST) is a frequently used method for evaluating whether a person has tuberculosis caused by the bacteria Mycobacterium tuberculosis. This test necessitates standardized processes, adequate training, and precise interpretation. 

How do we perform Tuberculin skin test?

Using a tuberculin syringe, 0.1 ml of tuberculin pure protein derivative (PPD) is injected into the inner surface of the forearm. The injection should be performed with the needle's bevel facing up. The precise injection placement should result in a pale elevation of the skin, generating a wheal 6 to 10 mm in diameter.

A skilled healthcare worker should read the skin test reaction 48 to 72 hours after the injection. For an accurate reading, patients must return within this time limit. The induration (firm swelling) in millimeters is used to assess the reaction, while erythema (redness) is ignored.

The tuberculin skin test reaction is interpreted based on two factors: the measurement of induration in millimeters and the individual's risk of TB infection or progression to TB disease if infected. The tuberculin skin test reaction can be classified as follows:

(Mantoux tuberculin skin test)

(This technician is in the process of correctly placing a Mantoux tuberculin skin test in this recipient’s forearm, which will cause a 6mm to10mm wheal, i.e., a raised area of skin surface, to form at the injection site. The Mantoux tuberculin skin test is used to evaluate people for latent tuberculosis (TB) infection. In the United States, this skin test consists of an intradermal injection of exactly one tenth of a milliliter (mL) of tuberculin, which contains 5 tuberculin units. Correct placement of this intradermal injection involves inserting the needle bevel slowly at a 5° to 15° angle. The needle bevel is advanced through the epidermis, the superficial layer of skin, approximately 3mm so that the entire bevel is covered and lies just under the skin surface. A tense, pale wheal that is 6mm to 10mm in diameter appears over the needle bevel.)

1. An induration of 5 or more millimeters is considered positive in the following groups:

   - People living with HIV

   - Recent contacts of individuals with infectious TB disease

   - People with chest X-ray findings suggestive of previous TB disease

   - Organ transplant recipients

   - Other immunosuppressed individuals (e.g., patients on prolonged corticosteroid therapy or taking TNF-a antagonists)

(The Mantoux test for TB involves intradermally injecting PPD (Purified Protein Derivative) tuberculin and measuring the size of induration 48-72 hours later.)

2. An induration of 10 or more millimeters is considered positive in the following groups:

   - People born in countries where TB disease is common

   - People who abuse drugs

   - Mycobacteriology laboratory workers

   - People living or working in high-risk congregate settings

   - People with certain medical conditions that increase the risk for TB

   - Children younger than 5 years of age

   - Infants, children, and adolescents exposed to adults in high-risk categories

3. An induration of 15 or more millimeters is considered positive in people with no known risk factors for TB.

False-positive reactions can arise as a result of past TB vaccination with the Bacillus Calmette-Guérin (BCG) vaccine, infection with nontuberculosis mycobacteria, improper measurement or interpretation of the reaction, or use of an inappropriate antigen. To avoid false-positive results, a TB blood test, also known as an interferon-gamma release assay (IGRA), is suggested in such instances.

False-negative reactions, on the other hand, can occur in people who are infected with M. tuberculosis but do not respond to the TST. Anergy (lack of immunological response), recent tuberculosis infection, young age (under 6 months), recent live-virus immunisation (measles or smallpox), inappropriate TST delivery, or measurement and interpretation problems are among factors that contribute to false-negative results.

The TST is a risk-free technique for the vast majority of people. Repeated TST placements are generally well-tolerated, and if a person fails to return for a reading within the stipulated time limit, a second test can be administered. When a second TST is conducted after an initial negative reaction, boosted reactions may occur in previously infected older persons, and this two-step testing strategy aids in precisely identifying a boosted reaction.

TST reactions can be hampered by live-virus vaccines such as measles, mumps, rubella, oral polio, varicella, yellow fever, BCG, and oral typhoid. To reduce interference, TST testing should be performed on the same day as the live-virus vaccine or at least one month afterwards.

It's worth noting that there are other tests for identifying tuberculosis infection, such as TB blood tests (IGRAs). The response to TB proteins is measured using a blood sample in these procedures. To avoid false-positive TST results caused by BCG vaccination, TB blood tests are preferred for persons aged 5 and up who have had the BCG vaccine.

Scanning electron micrograph of M. tuberculosis

Tuberculosis Vaccine (BCG Vaccine)

Understanding the BCG Vaccine

The Bacillus Calmette-Guérin (BCG) vaccine is a tuberculosis vaccine. It is made from a weakened strain of Mycobacterium bovis, which is linked to Mycobacterium tuberculosis. The BCG vaccine boosts the immune system to guard against tuberculosis.

Vaccination Process

In tuberculosis-endemic nations, the BCG vaccine is frequently provided during childhood. The vaccination is injected just beneath the skin in a little dose. The immune system develops a response that helps defend against tuberculosis infection over time.

(An apparatus (4–5 cm length, with 9 short needles) used for BCG vaccination in Japan, shown with ampules of BCG and saline)

Efficacy and Limitations

While the BCG vaccine provides some protection against severe tuberculosis in children, its efficacy against adult pulmonary tuberculosis is varied. The vaccination is more successful in avoiding severe types of tuberculosis in children, such as meningitis and disseminated illness.

Conclusion

Tuberculosis is a dangerous infectious disease that must be diagnosed and treated as soon as possible. Understanding the various treatment options, such as first-line and second-line medications, is critical for effective management. Furthermore, the Montaux and skin tests provide crucial diagnostic information, assisting in early detection and intervention. Furthermore, the BCG vaccine is critical in avoiding serious tuberculosis, particularly in high-risk areas. We can work towards a world free of tuberculosis by raising awareness, improving access to healthcare, and implementing preventive measures.

Frequently Asked Questions (FAQs)

1. Q: Is tuberculosis a highly contagious disease?

A: While tuberculosis is contagious, it typically requires prolonged and close contact for transmission to occur.

2. Q: Can tuberculosis be completely cured?

 A: With proper treatment and adherence to medication, tuberculosis can be cured in the majority of cases.

3. Q: Are there any side effects of the BCG vaccine?

  A: Common side effects of the BCG vaccine include a localized skin reaction at the injection site and swollen lymph nodes.

4. Q: Can tuberculosis be transmitted through sharing food or drinks?

  A: No, tuberculosis is primarily transmitted through respiratory droplets and does not spread through sharing food or drinks.

5. Q: Is tuberculosis more common in certain regions of the world?

  A: Tuberculosis is more prevalent in areas with limited access to healthcare, overcrowding, and poor sanitation.