1 Introduction to childhood tuberculosis
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When you have completed this unit you should be able to:
- Explain what tuberculosis is.
- Describe how TB bacilli are spread.
- Explain the difference between TB infection and tuberculosis.
- Explain why children are at high risk of TB infection.
- List communities in which tuberculosis is common.
- Explain the features of pulmonary tuberculosis.
- List the common forms of extrapulmonary tuberculosis.
1-1 What is tuberculosis?
Tuberculosis (TB or TB disease) is a chronic infectious disease which may involve many organs of the body, but most often affects the lungs. Tuberculosis of the lung is called pulmonary tuberculosis.
Tuberculosis is a chronic infectious disease.
1-2 What causes tuberculosis?
Tuberculosis is a bacterial illness caused by Mycobacterium tuberculosis. These bacteria are also referred to as TB bacilli (tuberculous bacilli).
Tuberculosis is caused by TB bacilli.
- Mycobacterium tuberculosis was first described by Robert Koch in 1882.
1-3 How are TB bacilli spread?
Tuberculosis is an infectious disease which results from the spread of TB bacilli from one person to another. TB bacilli are usually spread when a person with pulmonary tuberculosis talks, coughs, spits, laughs, shouts, sings or sneezes. This sends a spray of very small droplets from the person’s infected lungs into the air (i.e. airborne droplet spread). Live TB bacilli in these droplets then float in the air and may be breathed in by other people. If the inhaled TB bacilli reach the alveoli they cause a tuberculous infection of the lung.
1-4 Who usually spreads TB bacilli?
TB bacilli are usually spread from adults with untreated pulmonary tuberculosis. Therefore, a child with tuberculosis almost always has been in close contact with an adult with pulmonary tuberculosis (the source of the TB bacilli). It is less common for a child to catch tuberculosis from another child as children usually do not cough up TB bacilli in large numbers. Therefore, adults with untreated tuberculosis are a danger to children in the family or household.
TB bacilli that infect children are usually spread from an adult with untreated pulmonary tuberculosis.
- TB bacilli in unpasteurised or unboiled cows’ milk (Mycobacterium bovis) can be drunk and cause infection of the tonsil or gut, but this is very uncommon in South Africa.
1-5 Which children are at greatest risk of infection with TB bacilli?
Children, especially those under five years of age, who are exposed to large numbers of TB bacilli.
1-6 Which children are exposed to large numbers of TB bacilli?
Children who live in overcrowded, poorly ventilated homes or are exposed to crowded buses, taxis, schools, crèches and spaces where there are adults with untreated pulmonary tuberculosis. A child with tuberculosis often has an adult with untreated tuberculosis living in the same home. A mother with untreated pulmonary tuberculosis who is in close contact with her children is a great danger to her children.
Children in close, prolonged contact with adults who have untreated pulmonary tuberculosis are at greatest risk. Younger children are more likely to spend most of the day and night with an adult.
Children in poorly ventilated, overcrowded homes are at greatest risk of infection with TB bacilli.
1-7 Do all children infected with TB bacilli develop tuberculosis?
No. Most children infected with TB bacilli do not develop tuberculosis (TB disease) because their immune system is able to control the infection and kill most of the TB bacilli. As a result, the natural immune response protects most children with TB infection from progressing to tuberculosis.
It is very important to understand that a child can only develop tuberculosis if the child is first infected with TB bacilli. Furthermore, TB infection does not always progress to tuberculosis (TB disease). Therefore TB infection without further progression is not the same as tuberculosis.
Fortunately most children infected with TB bacilli do not develop tuberculosis.
The progression of TB infection to tuberculosis is more common in children than in adults.
1-8 Which children with TB infection are at the greatest risk of developing tuberculosis?
Children with a weak immune system are at the greatest risk. In these children, infection with TB bacilli may progress to tuberculosis because they have an inadequate immune system which is unable to control the infection. TB infection caused by large numbers of TB bacilli is also more likely to progress to tuberculosis.
Therefore, both TB infection and progress to tuberculosis are most common when a child with a weak immune system is exposed to large numbers of TB bacilli.
Children with weak immune systems are at greatest risk of tuberculosis.
1-9 Which children have weak immune systems?
Young children under five years, and especially if under two years, of age have immature (weak) immune systems which are unable to control severe infections. The immune system can further be weakened in:
- Children with HIV infection
- Children recovering from measles or whooping cough
- Children with severe malnutrition
- Children on large doses of oral steroids
HIV infection is the most important cause of a weakened immune system.
- Children less than 2 years of age and HIV-infected children are at high risk for progressing from TB infection to tuberculosis. They are also at the highest risk for developing severe forms of tuberculosis, notably tuberculous meningitis (TBM) and military tuberculosis.
Children with HIV infection have the highest risk of developing tuberculosis.
1-10 Is TB infection common?
Yes, infection with TB bacilli (Mycobacterium tuberculosis) is very common, and it is estimated that almost 50% of adult South Africans have been infected. Most infections take place during childhood.
TB infection is common and usually occurs during childhood.
1-11 How many children with TB infection develop tuberculosis?
Only about 10% of all people with TB infection progress to tuberculosis (TB disease) during their lifetime. Therefore, TB infection is far more common than tuberculosis.
The risk of TB infection progressing to tuberculosis is greater in young children than in older children or adults. In children infected under two years of age, the risk is as high as 50%.
About 10% of people with TB infection will develop tuberculosis.
1-12 What do you understand by the incidence of tuberculosis?
The incidence is the number of people who develop tuberculosis per 100 000 of the population per year. This is a very useful measure as it allows the frequency of tuberculosis in different communities or countries to be compared. The incidence of a single community can also be compared from one year to the next.
1-13 What is the incidence of tuberculosis in South Africa?
While tuberculosis is uncommon in most developed countries, it is common in developing countries such as South Africa where the number of people with tuberculosis has declined in the last few years. The incidence of tuberculosis in South Africa was 615/100 000 in 2019. This is high when compared to developed countries like the United Kingdom where the incidence of tuberculosis in 2019 was 8/100 000.
In South Africa tuberculosis is particularly common in the Western Cape and KwaZulu-Natal. In any clinic children will make up approximately 12% of all the cases of tuberculosis.
- About ten million new cases of TB occur worldwide each year with 12% in children less than 15 years of age. TB is the leading cause of death from a single infectious agent (ranking above HIV infection) having caused 1.4 million deaths in 2019. About 160 South Africans die of TB each day. With improving HIV care this figure is declining.
1-14 In which communities is tuberculosis common?
TB is common in poor, disadvantaged communities where overcrowding, undernutrition and HIV infection are common. Tuberculosis is a disease of poverty. Tuberculosis spreads in any overcrowded living spaces, both at home and in the community. TB is often transmitted by a child’s family member, friend or close neighbour. However it may also be caught in a public space if there are many untreated patients in the community.
Tuberculosis is usually seen in poor communities.
- About 95% of new TB cases and 99% of TB deaths worldwide are in developing countries. In developed countries TB is virtually confined to poor, overcrowded environments and ethnic minorities.
1-15 Why is tuberculosis an important disease?
Tuberculosis is a major cause of illness and death in many poor countries. These are preventable deaths, and the large number of patients with tuberculosis is a huge drain on healthcare resources.
Tuberculosis is an important cause of illness and death.
1-16 What is primary TB infection of the lung?
Tuberculous infection usually starts when TB bacilli are inhaled deep into the distant parts of the lungs, called alveoli. During the first six weeks of infection the immune system is unable to control the TB bacilli, which multiply rapidly in the alveoli where they cause a small, local area of inflammation. This is called primary tuberculosis. From the primary infection TB bacilli spread along the lymphatics to the local lymph nodes at the place where the main bronchi divide into branches (hilar nodes). The primary infection in the lung, together with the infected hilar lymph nodes, is called the primary complex. Parahilar and other mediastinal nodes may also be affected.
After six weeks the immune system usually becomes active and kills most of the TB bacilli in the lung and lymph nodes. As a result, the primary infection is asymptomatic in most children and does not cause clinical illness.
Therefore, the primary TB infection usually heals and does not spread any further, as the TB bacilli have been contained by the body’s natural immunity.
- The primary TB infection in the lung used to be called the Ghon focus.
Inhaling TB bacilli into the lung may result in primary infection.
1-17 Can the primary TB infection cause illness due to spread of the infection within the lung?
Sometimes the primary TB infection is not controlled by the immune system and the child now becomes ill with the signs and symptoms of pulmonary tuberculosis. This is a common form of tuberculosis in children.
With progression of the primary infection to pulmonary tuberculosis, the TB bacilli continue to multiply and an area of inflammation develops in the lung and lymph nodes in an attempt to prevent the TB bacilli from spreading any further. Often the centre of the inflamed area becomes soft as the tissues die. These dead cells (caseous material) can drain into the surrounding tissues.
There are a number of different ways that the primary TB infection can spread (progress) and lead to complications.
The primary TB infection may spread to cause pulmonary tuberculosis.
- The immune response to TB bacilli is dependent on T lymphocytes.
1-18 What are the pulmonary complications of the primary TB infection in the lung?
- In some children with a weak immune system, the body is unable to control the primary infection in the lung. The TB bacilli continue to multiply and spread into neighbouring parts of the lung to cause tuberculous pneumonia. Progression from the primary infection to pulmonary tuberculosis usually takes place rapidly within weeks or months and the child becomes ill. This pattern of tuberculosis, together with enlarged hilar nodes, is the commonest form of tuberculosis in young and undernourished children.
- Cavitary tuberculosis (‘open tuberculosis’) is usually seen in older children and adolescents. The area of tuberculous pneumonia progresses and breaks down to form a hole. This occurs most commonly in the upper parts of the lung and results in an air-filled cavity containing dead (caseous) tissue which contains huge numbers of TB bacilli. This form of pulmonary tuberculosis is very infectious as TB bacilli grow fast and many TB bacilli enter the airways. From here they are coughed into the air where they may be breathed in and infect the lungs of other people. Children and adolescents with cavitary tuberculosis are very infectious and can infect other children and adults.
- Damage to the large airways by tuberculosis can result in bronchiectasis.
- In older children and adults the TB bacilli often remain dormant (inactive or ‘sleeping’) in the lung for many months or even years after the primary infection. The body has been able to control but not kill all the TB bacilli. If the immune system later becomes weakened by malnutrition or another infection, such as HIV or measles, the TB bacilli may start to multiply once more (reactivation) and a local area of tuberculous pneumonia will develop. Therefore, pulmonary tuberculosis due to reactivation of dormant TB bacilli may only present years after the primary infection.
Pulmonary tuberculosis with enlarged hilar lymph nodes is the commonest form of tuberculosis in children.
1-19 What are the pulmonary complications of TB infection in the hilar lymph nodes?
- TB bacilli may multiply rapidly in the hilar lymph nodes, causing the nodes to enlarge and compress the bronchus or trachea (airway). Clinically this may present as wheezing or stridor with either collapse or hyperinflation of a lobe or the whole lung.
- The enlarged lymph node may rupture into a bronchus spreading large numbers of TB bacilli into other areas of the lung. This results in widespread tuberculous bronchopneumonia.
Enlarged hilar lymph nodes may compress the airways causing wheezing.
1-20 Why are the lungs the commonest site of tuberculosis?
The lungs are the commonest site of tuberculosis as TB infection is usually caused by inhaling TB bacilli.
1-21 What is the difference between pulmonary tuberculosis in children and adults?
While children usually have lymph node enlargement with few TB bacilli in the sputum, adolescents and adults usually have cavitary tuberculosis with destruction of lung tissue and large numbers of TB bacilli in their sputum.
- Cavities are formed in adult-type tuberculosis, usually in the upper lobes or apices of the lower lobes of the lungs. This can result in permanent lung damage and scarring (fibrosis).
1-22 Can tuberculous infection spread from the lung to other parts of the body?
Yes. This spread beyond the lungs is called extrapulmonary tuberculosis:
- Tuberculosis may spread from the lung to the pleura causing a pleural effusion.
- Infection with TB bacilli can spread from the lung, and especially the hilar lymph nodes, via the bloodstream (TB bacteraemia) to most organs of the body. In children the TB bacilli usually spread at the time of the primary lung infection. As a result, tuberculosis of other organs usually presents soon after the primary lung infection. However, the TB bacilli may remain dormant in these organs for many months or years before they start to multiply and cause local tuberculosis. This reactivation of TB bacilli is usually due to weakening of the immune system.
- TB bacilli can also spread to other lymph nodes via the lymphatics (e.g. from the hilar lymph nodes up to the cervical lymph nodes or down to the abdominal lymph nodes). Lymph nodes in the axilla or groin may also be involved. However, lymphatic spread is usually to the cervical nodes. TB infection of lymph nodes is called tuberculous lymphadenitis.
Tuberculous bacilli may spread from the lungs to other organs via the bloodstream or the lymphatics.
1-23 Which other organs can be involved in tuberculosis?
Although the lung is the commonest organ infected by TB bacilli, tuberculosis can involve any other organ of the body. Sometimes more than one organ is infected. The organs which are most commonly infected via the bloodstream in children are:
- The meninges (tuberculous meningitis)
- Bones, especially the spine (tuberculous osteitis)
- Joints, especially the hip joint (tuberculous arthritis)
- Intra-abdominal organs such as liver and spleen and peritoneum (abdominal tuberculous)
- The skin, tonsils, pericardium, bone marrow, middle ear and genitalia are less common sites of tuberculosis in children. Tuberculosis of the kidney usually follows five or more years after the primary infection and therefore is uncommon in childhood.
1-24 What is disseminated tuberculosis?
Tuberculosis involving multiple organs is referred to as disseminated tuberculosis. This follows spread of TB bacilli through the bloodstream to many organs. If disseminated tuberculosis includes widespread infection of both lungs, it is called miliary tuberculosis. This is a very serious illness with a high mortality rate unless diagnosed and treated early. It usually occurs in young children.
Disseminated tuberculosis is a serious illness with a high mortality rate.
1-25 Is extrapulmonary tuberculosis infectious?
Unlike pulmonary tuberculosis, tuberculosis of other organs is rarely infectious to other people.
1-26 Is extrapulmonary tuberculosis common in children?
Yes, extrapulmonary tuberculosis is far more common in children than in adults. Cervical lymph node enlargement is the commonest form of extrapulmonary tuberculosis in children.
Cervical lymph node enlargement is the commonest form of extrapulmonary tuberculosis in children.
1-27 Can one have a tuberculous infection more than once?
Yes. Previous TB infection does not give complete immunity to further TB infections. A child with a healed primary infection can, months or years later, have another new primary infection when they are exposed to an infectious case of tuberculosis, especially if their immune system is weakened by severe malnutrition or HIV.
Therefore, pulmonary tuberculosis may be due to immediate spread from the original primary infection, reactivation (relapse) of an old primary infection which had not healed fully (latent tuberculous infection), or spread from a new primary infection (reinfection). In children, spread from the primary TB infection to cause tuberculosis is most common and usually occurs within two years of being infected (90% within one year of being infected).
1-28 Can a mother with tuberculosis infect her infant either before or after birth?
Yes. During pregnancy TB bacilli in the mother can be spread via the bloodstream to the placenta. From here the TB bacilli may reach the fetus via the umbilical vessels or may infect the amniotic fluid and then be swallowed by the fetus. Infection during delivery is rare.
However, the spread of TB bacilli from a mother to her infant usually happens after delivery. The greatest risk is for an infectious mother to cough over her newborn infant. TB bacilli do not appear in the breast milk. Therefore breastfeeding is safe as long as the mother is on treatment and the infant receives prophylaxis.
Case study 1
A child of six years develops primary TB infection in her one lung. She remains clinically well however. When she is weighed by the school nurse, the mother is reassured that the child is healthy and thriving.
1. What is the cause of TB infection?
TB bacilli (Mycobacterium tuberculosis).
2. Why is this child clinically well if she has a primary TB infection?
Because most children with a primary TB infection have no signs or symptoms of illness. Her immune system has controlled the TB infection.
3. Will this child develop tuberculosis?
Probably not, as most children are able to prevent the spread of TB bacilli from the primary infection.
4. Which children are at greatest risk of the primary infection progressing to tuberculosis?
Children with weak immune systems. These include young children, malnourished children and children with HIV infection.
5. How common is TB infection?
Very common. Almost 50% of adult South Africans have had a primary TB infection at some time in their lives, most during childhood.
6. How many children with TB infection develop tuberculosis?
The risk of progression from TB infection to tuberculosis during a lifetime is about 10%. However the risk is higher in children and is as high as 50% in children under two years of age. Therefore TB infection is particularly dangerous in young children.
Case study 2
An 18-month-old child lives in an overcrowded home. During the day he is looked after by his grandfather who is unwell and has had a chronic cough for the past few months. The clinic nurse is worried as the child is malnourished and recently had measles.
1. Why is this child at high risk of TB infection?
Because the grandfather probably has undiagnosed pulmonary tuberculosis. The house is overcrowded and the child has prolonged contact with the grandfather. These factors all suggest that the child is being exposed to large numbers of TB bacilli.
2. Why will the TB infection probably progress to tuberculosis?
Because the child has a weak immune system due to his young age, malnutrition and recent measles infection.
The child’s age and exposure to large numbers of TB bacilli will, therefore, increase his risk of both TB infection and progress to tuberculosis.
3. What other infection may weaken the immune system?
4. Is childhood tuberculosis common in South Africa?
Yes, especially in poor, disadvantaged communities. Childhood tuberculosis makes up approximately 12% of all the cases at a TB clinic.
5. What are the pulmonary complications of primary TB infection in the lung?
The primary infection in the lung may progress to tuberculous pneumonia. In older children and adults this may form a cavity. The grandfather probably has cavitary tuberculosis.
6. Are the hilar lymph nodes often involved in primary TB infection?
Yes. The primary TB infection in the lung is usually associated with enlarged hilar lymph nodes. Together they are called the primary complex. The enlarged hilar nodes can compress a large airway causing wheeze or stridor. Further enlargement of the lymph nodes may result in collapse or overinflation of a lobe.
Case study 3
The parents are very worried as their daughter has a lump in her neck which has been diagnosed as tuberculosis. Friends tell them that the diagnosis must be wrong as tuberculosis only affects the lungs.
1. Does tuberculosis only affect the lungs?
No. Tuberculosis may affect most organs of the body. Tuberculosis outside the lungs is called extrapulmonary tuberculosis.
2. What is the likely cause of the lump in her neck?
Tuberculosis of a lymph node (tuberculous lymphadenitis).
3. What other organs are most commonly infected with TB?
The meninges (TB meningitis), bones (TB osteitis), joints (TB arthritis) and abdominal organs (abdominal TB).
4. What is disseminated tuberculosis?
The spread of TB infection to many organs. This is a serious illness with a high mortality rate.
5. Is extrapulmonary tuberculosis infectious to others?
Usually not. However, extrapulmonary and pulmonary TB may occur in the same patient. Pulmonary tuberculosis is the most infectious form of the disease.
6. Can a newborn infant be infected with tuberculosis from the mother?
Tuberculosis can spread from mother to infant during pregnancy but this is uncommon. The greatest risk is when a mother with tuberculosis coughs onto her newborn infant.
The five most important ‘take-home’ messages
- Children are infected with TB bacilli after exposure to someone with infectious pulmonary tuberculosis.
- Most TB infection in children does not progress to disease (tuberculosis).
- The children at greatest risk of progression to disease are children infected when less than two years of age, HIV infected children, and children with malnutrition.
- Pulmonary tuberculosis with enlarged hilar lymph nodes is the commonest form of tuberculosis in children.
- Cervical lymph node enlargement is the commonest form of extrapulmonary tuberculosis in children.