Tuberculosis

What is Tuberculosis?

Tuberculosis (TB) is a dreaded bacterial infection. It has been known to mankind since ancient ages. It was commonly called “consumption” at the turn of the last century because of the way the disease seemed to “consume” the individual it affected.

Causes and spread of the infection

The bacteria causing tuberculosis is called Mycobacterium tuberculosis. It is spread through inhaling tiny droplets from the coughs or sneezes of an infected person. Spread of tuberculosis is facilitated by several factors like overcrowding, living in close quarters like in orphanages, prisons etc. and presence of other medical problems.

Other medical problems that raise the risk of getting tuberculosis include malnutrition, alcoholism, presence of other infections like HIV infection that suppresses the immunity etc. Babies and the elderly are at a greater risk due to their ill-developed and declining immune system respectively.

Under a high magnification of 15549x, this colorized scanning electron micrograph (SEM) depicted some of the ultrastructural details seen in the cell wall configuration of a number of Gram-positive Mycobacterium tuberculosis bacteria. As an obligate aerobic organism M. tuberculosis can only survive in an environment containing oxygen. This bacterium ranges in length between 2 - 4 microns, and a width between 0.2 - 0.5 microns.

What is latent and active tuberculosis?

Getting the active disease means that the immune system fails to kill or contain the infection allowing it to spread to the lungs or other parts of the body. This is called active tuberculosis.

In some individuals the immune system cannot kill the bacteria, but manages to prevent it from spreading in the body. This can mean persistence of the bacteria in the body without producing symptoms. This is called latent tuberculosis.

When this is present, a decline of damage to the immune system may cause the infection to flare up to give rise to frank and active tuberculosis.

Symptoms and types of tuberculosis

Tuberculosis mainly affects the lungs where it is called pulmonary tuberculosis. It can affect any part of the body including bones, brain, womb or the uterus, skin, lymph nodes etc. or may spread widely to other organs as seen in miliary tuberculosis and disseminated tuberculosis.
Typical symptoms of pulmonary tuberculosis include:-

  • continued or a persistent cough of more than three weeks that brings up phlegm 
  • presence of streaks or drops of blood in the coughed up phlegm or sputum
  • weight loss and fatigue and loss of appetite
  • fever for a long duration that is not explained by any other cause
  • night sweats

Diagnosis of tuberculosis

Tuberculosis is diagnosed using several laboratory techniques that test samples of blood and sputum. The bacteria can be found on staining and microscopic examination of the sputum.

More rapid and sophisticated blood tests are also available to test for tuberculosis. A chest X ray is used to visualize the tubercular lesions in the lungs. CT scan and MRI images may also be used for diagnosis.

For tuberculosis affecting lymph nodes, skin etc, the local lesion may be biopsied to detect tuberculosis bacteria.

Treatment of tuberculosis

With treatment, a TB infection can usually be cured. Treatment involves a course of antibiotics, usually for six months. More than one antibiotic is used to prevent emergence of resistance of the bacteria to the antibiotics. Those infected with a drug resistant form of tuberculosis may be prescribed a longer course of antibiotics.

Tuberculosis vaccine

The Bacillus Calmette-Guérin (BCG) vaccine can provide effective protection against tuberculosis in most individuals. It is recommended in persons who are at a greater risk of the infection. Infants living in countries endemic for tuberculosis are routinely vaccinated with BCG.

Tuberculosis epidemiology

TB was a major health problem in most of the developed countries like the UK before the development of antibiotics. The number of cases has declined sharply after routine detection and use of antibiotics. However, in the last two decades cases of tuberculosis have gradually increased, especially among ethnic minority communities and immigrant population.

In 2011, 8,963 cases of tuberculosis were reported in the UK (around 12 cases per 100,000 population). Of these nearly 6,000 cases were among population who were born outside the UK. There are many areas in the UK with much higher incidence rates, and those areas with incidence greater than 40/100,000. Pulmonary TB accounts for 60% of TB in the UK.

Tuberculosis is endemic in many developing and under-developed countries. Africa, particularly sub-Saharan Africa still suffers from a tuberculosis epidemic because of the increased susceptibility of the population due to concomitant HIV infection.

Tuberculosis Causes

Tuberculosis is an infectious disease and is caused by a type of bacterium called Mycobacterium tuberculosis. One-third of the world's population is infected with the bacterium that causes tuberculosis. Each year about nine million people develop the disease and up to nearly two million people worldwide are killed by it.

How is TB spread?

The infection is spread when a person with an active TB infection in their lungs coughs or sneezes near a person without the infection. The bacterium is released in the expelled droplets and is inhaled by the healthy person.

Tuberculosis, however, is not a contagious disease unlike other infections like flu, the common cold etc. It affects people with a lowered immunity more commonly than those with an intact immune system.

Risk factors for TB

Risk factors associated with getting tuberculosis include:-

  • People living in areas with a high prevalence of tuberculosis.
  • People who work closely or live close to a person with infectious tuberculosis. This includes healthcare workers and people living in crowded living spaces. Children in schools and prisoners living in closed confined spaces are at a greater risk.
  • Travellers to areas with high incidence of tuberculosis and immigrants from countries with high incidence are at risk of bringing the infection to countries where the prevalence of the condition is lower.
  • Those with other infections like HIV have a lower capacity to fight off tuberculosis. This is mainly due to depressed immune system caused by the concomitant HIV infection. Those with medical conditions such as diabetes, immune disorders, end-stage renal disease, gastrectomy/jejuno-ileal bypass, those taking drugs like corticosteroids for long durations, those on chemotherapy for cancer and other drugs that suppress immunity (e.g. drugs used after organ transplants) are at a greater risk of tuberculosis.
  • Immature immunity for example in babies and declining immunity in the elderly makes both these age groups susceptible to tuberculosis. Pregnant women are also at a greater risk due to lowered immunity.
  • Malnutrition with a poor health or having a poor diet due to lifestyle, drug abusers, alcoholics, those living in poverty, the homeless etc. are more at risk of tuberculosis.

Tuberculosis Diagnosis

There are several investigations that may be used to diagnose tuberculosis. This may depend on the type of tuberculosis that is suspected.

Pulmonary tuberculosis

In this type of tuberculosis the lesion more often than not lies in the lungs. A Chest X ray shows the lesion within the lungs. There may be scarred appearance of the lungs.

Primary tuberculosis usually appears in the central upper portion of the lungs with a pleural effusion or collection of fluid around the lungs. In severe disease there may be a picture like millet seeds over the X ray plate of the lungs. This is called milliary tuberculosis.

The phlegm or mucus is collected from the patient. It is placed onto a glass slide and stained with a special dye called the Ziehl-Neelson stain and then viewed under the microscope. The tubercle bacilli show up as tiny red thread like organisms.

For examination of sputum at least 3 spontaneous sputum samples need to be examined for culture and microscopy. Culture results may take time to come and treatment with anti tubercular drugs may be started on the basis of microscopy if there are symptoms of tuberculosis. Sputum is cultured on a medium called the Löwenstein-Jensen slope which takes 4-8 weeks due to slow bacterial growth.

Samples should include at least one early morning sample. In the case of children, or in those who cannot produce a sputum or phlegm sample, the washings of the bronchus and air passages are taken using bronchoscopy, lavage and gastric washings. These samples are then tested for the bacteria. Samples need to be taken before starting treatment or within 7 days of starting.

Extra-pulmonary tuberculosis or tuberculosis outside the lungs

In patients with tuberculosis suspected outside the lungs several tests are suggested. These include:

  • A computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan of the part of the body affected or of the whole body to look for other focus of the disease.
  • An ultrasound scan of the abdomen and other hollow parts of the body that may be affected may also give clues.
  • Series of routine and special blood tests to detect tuberculosis.
  • Urine tests for the bacteria if the urinary tract is affected.
  • Biopsy of the affected tissues and parts of the body and examination of the sample under the microscope helps detects the presence of the disease.
  • Those with suspected tuberculosis of the nervous system or of the brain and meninges (layers of cells that cover the brain and the spinal cord) also need a lumbar puncture. This involves taking a small sample of cerebrospinal fluid (CSF) from the base of the spine. This CSF is a clear fluid that bathes and surrounds the brain and the spinal cord. The fluid is checked under the microscope of using biochemical tests to detect tuberculosis.

Ruling out other diagnoses

Diagnosis that need to be ruled out while confirming tuberculosis include:-

  • Cancers
  • Lymphoma
  • Pneumonia
  • Fibrotic lung disease (e.g. Sarcoidosis, silicosis etc.)
  • Diabetes

 

Tuberculosis Prevention

Tuberculosis is a preventable and a curable disease if detected and treated early. It has a low prevalence in developed nations including the United Kingdom and the United States. This means people living in these countries and areas with low prevalence need not take precautions to prevent the infection. However, some measures of prevention are suggested for those living or travelling to areas and countries that have a high prevalence of the infection.

Tuberculosis vaccine

Bacillus Calmette-Guérin (BCG) vaccination can protect against tuberculosis. The BCG vaccine is given to all infants in countries where the disease is prevalent. In countries like the UK where it is less common it is given to those who are at risk.

Before the vaccine is given, the person is given a Mantoux skin test to check for latent tuberculosis. Vaccination is not recommended for people with latent tuberculosis.

Who is the BCG vaccine recommended for?

Currently, the BCG vaccination is recommended for three main groups of people. One of these are babies born in areas where the rates of tuberculosis is high and those babies with one or more parents or grandparents born in countries with a high rate of tuberculosis. Mantoux skin test will not be required beforehand while giving BCG vaccine to a baby.

Another group that needs BCG vaccine includes children under 16 years of age who have one or more parents or grandparents born in countries with a high rate of tuberculosis and have not been vaccinated as babies. Children under 16 who have been in close contact with someone with tuberculosis or have lived for at least three months in a country with a high rate of tuberculosis are also vaccinated with BCG after getting a Mantoux test.

The third group that requires BCG vaccination are those at high-risk occupations that includes people under 35 years of age whose occupation expose them to tuberculosis infected persons. This includes:-

  • health care workers (doctors, nurses and carers)
  • laboratory personnel who handle samples of tuberculosis
  • veterinary staff and other animal workers, such as abattoir workers who handle animals that may carry tuberculosis
  • those working in closed cramped spaces including prisoners, and hostel wardens, staff at orphanages and homes for the homeless etc.
  • staff at elderly care homes and refugee homes
  • travellers to countries with high rates of tuberculosis who plan to live there for at least 3 months

Prevention of transmission of infection

Those with pulmonary tuberculosis are contagious up to about two to three weeks once their treatment is begun. Earlier these patients were isolated. These days isolation is not practiced but some precautions are important to prevent spread. These include:-

  • Isolation from workplaces, schools and college and areas with crowds.
  • Covering one’s mouth and nose while coughing or sneezing.
  • Adequate and careful disposal of tissues. Usually burning or disposal in sealed plastic bags is recommended.
  • Sharing beds and rooms with un-infected persons while sleeping should be avoided.

Getting treatment for latent infections

Contacts of tuberculosis patients are evaluated for latent tuberculosis. Latent tuberculosis is suspected if they are:-

  • Interferon-gamma positive OR
  • Mantoux positive (either 6 mm or greater without prior BCG vaccination or strongly positive (≥15 mm) with prior BCG vaccination), OR
  • Presence of tuberculosis nodules on chest X ray without history of adequate treatment

These latent tuberculosis patients need to be treated with anti-tubercular drugs to prevent spread and flaring up of the infection. Treatment is either six months of isoniazid or three months of rifampicin and isoniazid combination.

If the person exposed to tuberculosis is HIV positive 6 months of isoniazid is preferred. Those who have been exposed to people with isoniazid-resistant tuberculosis get 6 months of rifampicin.