Tuberculosis and Its Diagnosis

Kanchan Srivastava and Surya Kant

Tuberculosis (TB) has been known to mankind since ancient times. TB is one of the oldest recorded and main causes of death of human beings. Earlier this disease has been called by numerous names including consumption (because of the severe weight loss and the way the infection appeared to “consume” the patient), phthisis pulmonaris and the white plague (because of the extreme pallor seen among those infected). In the nineteenth century, TB was known as “the captain of all men of death”. It is still true to a large extent today 1- 4 .

TB is curable and preventable but still kills approximately three people every minute 3. India is considered as the second-most populous country in the world with one-fourth of the global incident TB cases annually (TB India 2014). The numbers are over 90% in the developing world 5. Even today after the development of advanced screening, diagnostic and treatment methods for the disease, a third of the world’s population has been exposed and is infected with the organism.


Tuberculosis in Ancient times

The organism causing TB - Mycobacterium tuberculosis (MTB) existed 15,000 to 20,000 years ago. It has been found in relics from ancient Egypt, India, and China. Among Egyptian mummies spinal tuberculosis, known as Pott’s disease has been detected by archaeologists. Evidence of TB of the cervical lymph nodes or lymph nodes of the neck termed scrofula, is found in the middle ages. It was termed as the “king’s evil”. Poorly ventilated and overcrowded housing, primitive sanitation, malnutrition and other risk factors led to the rise. The term White plague emerged around this time 6, 7.


Discoveries pertinent to tuberculosis

The tubercle bacilli or the causative organism of TB was discovered by Robert Koch in 1882. He showed that the organism’s unique protein coat made it difficult to visualize earlier until a specific stain called the Zeihl Neelson (ZN) stain was discovered 8. The bacteria was called Koch’s bacillus and since it took up the red acidic dye, it was called AFB or acid fast bacilli. Koch was awarded the Nobel Prize in 1905 9. In 1895 Wilhelm Roentgen developed X- rays which further advanced diagnostics of TB. This allowed early diagnosis and isolation of infected individuals.The early symptoms of activeTB include;


Symptoms

• Fatigue
• Recurrent fever
• Unusual weight loss
• Breathlessness
• Coughing
• Night sweats and
• Sometime blood in cough.


Transmission

TB is a disease that is spread through the air from one person to another. Although transmission of bacterium from infected person may not always result in disease. It mainly depends upon the number of droplet nuclei expelled from the infected person into the air.
Active TB means that the TB bacteria are growing and causing symptoms. If the lungs are infected with active TB, it is easy to spread the disease to others. TB spreads when a person who has active disease exhales air that contains TB-causing bacteria and another person inhales the bacteria from the air. These bacteria can float in the air for several hours 10.Coughing, sneezing, laughing, or singing releases more bacteria than breathing. If TB is present in organs other than the lungs (Extra pulmonary tuberculosis; EPTB), it does not spread easily (i.e., It is less contagious). The specific symptoms will depend on whether the infection is in the lungs or in another part of the body (EPTB). There are two types of TB:


TB disease

People with TB disease can spread the bacteria to others, feel sick, and can have symptoms including fever, night sweats, cough, and weight loss.


Latent TB infection

TB bacteria can live in the body without making a person sick. People with latent TB infection do not feel sick, do not have TB symptoms, and cannot spread TB bacteria to others. Some people with latent TB infection go on to develop the disease.


Who Should Get Tested for TB?

TB tests are generally not needed for people with a low risk of infection with TB bacteria. Certain people should be tested for TB bacteria because they are more likely to get TB disease, including:
• People who have spent time with someone who has TB disease
• People with HIV infection or another medical problem that weakens the immune system
• People who have symptoms of TB disease (fever, night sweats, cough, and weight loss)
• People from a country where TB disease is common.
• People who live or work somewhere TB disease is more common (homeless shelters, prison or some nursing homes)
• People who use illegal drugs


Tuberculosis Diagnosis: How is TB Detected?

TB is diagnosed by finding MTB bacteria in a clinical specimen taken from the patient 11. People suspected of having TB disease should be referred for a complete medical evaluation, which will include
• Medical history,
• Physical examination,
• Chest radiograph (X-ray) and scans
• Test for TB infection (TB skin test or TB blood test),
• Appropriate laboratory tests/ Microbiological examinations/ surgical biopsy.


Medical history:

The medical history includes obtaining the symptoms of pulmonary TB: productive, prolonged cough of three or more weeks, chest pain, and hemoptysis. Systemic symptoms include low grade remittent fever, chills, night sweats, appetite loss, weight loss, easy fatigability, and production of sputum that starts out mucoid but changes to purulent.
Other parts of the medical history include prior TB exposure, infection or disease; past TB treatment; demographic risk factors for TB; and medical conditions that increase risk for TB disease such as HIV infection. Depending on the sort of patient population surveyed, as few as 20%, or as many as 75% of PTB cases may be without symptoms .12 TB should be suspected when a pneumonia-like illness has persisted longer than three weeks, or when a respiratory illness in an otherwise healthy individual does not respond to regular antibiotics.


Physical examination:

A physical examination is done to assess the patient's general health and find other factors which may affect the TB treatment plan. It cannot be used to confirm or rule out TB. However, certain findings are suggestive of TB.


Radiology: Chest X-ray and CT

TB creates cavities visible in x-rays in the patient's lungs.Lesions may appear anywhere in the lungs:
• In active PTB, infiltrates or consolidations and/or cavities are often seen in the upper lungs with or without mediastinal or hilar lymphadenopathy or pleural effusions (tuberculous pleurisy).
• In disseminated TB a pattern of many tiny nodules throughout the lung fields is common - the so-called miliary TB.
• In HIV and other immunosuppressed persons, any abnormality may indicate TB or the chest X-ray may even appear entirely normal.
• Abnormalities like development of lesions in the lungs are to be suspected in TB.
• Cavitation or consolidation of the apexes of the upper lobes of the lung or the tree-in-bud sign may be visible on an affected patient's chest X-ray. These lesions are of different sizes, shape, density, and cavitations. Chest radiographs helps in the evaluation of Cavitary and non-cavitary areas in lungs and are according to American Thoracic Society (ATS), classified as mild, moderate and far advance 13.

Computerized Tomography

(CT scans) and Magnetic Resonance Imaging (MRI) have proved for useful for imaging TB lesions particularly in the brain and spine.

Abreugraphy

A variant of the chest X-Ray, Abreugraphy (from the name of its inventor, Dr. Manuel Dias de Abreu) was a small radiographic image, also called miniature mass radiography (MMR) or miniature chest radiograph. Though its resolution is limited (it doesn't allow the diagnosis of lung cancer) it is sufficiently accurate for diagnosis of TB.
Much less expensive than traditional X-Ray, MMR was quickly adopted and extensively utilized in some countries, in the 1950s.


Immunological Tests:

There are two kinds of tests that are used to determine if a person has been infected with TB bacteria: The tuberculin skin test and TB blood tests.


Tuberculin Skin Test (TST)

The Mantoux tuberculin skin test is a test to check if a person has been infected with TB bacteria. Using a small needle, a health care provider injects a liquid (called tuberculin) into the skin of the lower part of the arm. When injected, a small, pale bump will appear. This is different from a Bacilli Calmette-Guerin (BCG) shot (a TB vaccine that many people living outside of the United States receive). The person given the TST must return within 2 or 3 days to have a trained health care worker look for a reaction on the arm where the liquid was injected. The health care worker will look for a raised, hard area or swelling, and if present, measure its size using a ruler. Redness by itself is not considered part of the reaction.


Positive TST results mean;

The TST result depends on the size of the raised, hard area or swelling. It also depends on the person’s risk of being infected with TB bacteria and the progression to TB disease if infected. • Positive TST: This means the person’s body was infected with TB bacteria. Additional tests are needed to determine if the person has latent TB infection or TB disease. • Negative TST: This means the person’s body did not react to the test, and that latent TB infection or TB disease is not likely.