What causes a persistent cough in children?

Cough isn’t usually a reason to worry as it’s your child’s normal response to airway irritation from all manner of normal stimuli, both from within their own body and from outside. Dr Chinedu Nwokoro is a leading respiratory paediatrician and here he shares what the possible causes of a persistent cough are in kids.
 

Why do we cough?

The primary purpose of a cough is protective. When we cough we forcefully expel air from our lungs, carrying with it noxious or harmful agents such as inhaled liquids or foodstuffs (when a mouthful goes the “wrong way”) or inflammatory cells and mucous generated by the immune system in the fight against viruses and bacteria (phlegm).
 

We can also cough as a maladaptive (unhelpful) response to triggers such as allergens (like pollens and dust or food allergens) or irritants like strong perfumes, pepper, dust and smoke, which can cause narrowing of the airways like that seen in asthma and other allergic diseases.
 

What are the possible causes of persistent cough?

There are many possible causes, which I have divided into broad groups and will outline here:

Infection
This is the most obvious cause of persistent cough in children and can be divided into:

• Post-infectious cough
  Infections with pertussis (the bacterium that causes whooping cough) and mycoplasma, both so-called ‘atypical’ causes of chest infection, can cause a cough that can last several months.
  
  There may have been a triggering illness with paroxysms of coughing and perhaps vomiting. The classic ‘whoop’, (where the child takes a deep breath in after a run of uncomfortable coughing) may be absent in older and vaccinated children. In both these cases, the cough is usually dry, and the child looks well after the initial illness has settled.
  
  Depending on the timing of testing it may be possible to find evidence of infection with these bugs but often they are not diagnosed.
  
  There is no really effective treatment for this post-infectious cough but paracetamol may relieve the pain associated with a persistent cough. Homemade remedies with honey and lemon have a genuine role, and various over-the-counter cough remedies are popular without an overwhelming research justification.
   
• Persistent bacterial bronchitis
  This is a condition where a child develops a wet or 'rattley' cough, perhaps after a viral cold, which lasts for in excess of 4-8 weeks. Children will rarely cough up phlegm, and diagnosis is by cough swab (the child coughs onto a bacterial swab held in their open mouth).
  
  This will usually respond to a prolonged (2-4 weeks) course of broad-spectrum antibiotics by mouth and does not usually need further testing or treatment.
   
• Tuberculosis (TB)
  This is a rarer cause and is more common in children with prolonged (household) contact with adults with TB of the lung or from countries where TB occurs frequently.
  
  These children will have a prolonged low-grade fever and may have night sweats, weight loss and enlarged lymph nodes. Diagnosis involves skin tests, blood tests, X-ray, as well as careful history and examination. Treatment is a specialist endeavour and you should see your child’s GP if you feel that this is a possibility.

Allergic causes
Allergy is when the immune system mounts an over-the-top response to otherwise harmless triggers known as allergens. It can affect the respiratory tract, the gut and the skin and can be rapid and dramatic or slower and more difficult to recognise.
 

• Asthma
  Children with asthma will often cough for longer than expected, particularly following a viral cold or chest infection. The cough is usually dry, may be associated with wheeze and is worse at night or with exercise.
  
  The child may additionally have hayfever, eczema, or food allergy. They will usually improve from day-to-day with inhaled salbutamol (the blue puffer) with consideration of the use of preventer treatment in children who need to use their blue puffer more than three times in an average week.
  
  Diagnosis is via a careful assessment of symptoms, triggers, response to treatment trial, as well as by measurement of lung function with spirometry and exhaled nitric oxide (in older children).
   
• Upper airway cough syndrome (or postnasal drip)
  This is a condition where children have a mainly nighttime cough, driven by nasal inflammation (rhinitis) which is present even when they don’t have a cold. They may also have reduced hearing or ear infections due to clogging of the ear canals with this inflammatory fluid.
  
  When these children lie down to sleep the nasal fluid drips down and irritates the throat causing a cough that may be wet or dry. The nasal symptoms are often triggered by irritation by allergens such as dust, pollens, moulds or animal dander, but may also occur in the context of gastric reflux, the aerosol from which can irritate the nasal lining.
  
  Children may benefit from the removal of their allergic triggers, from the treatment of rhinitis with antihistamine, nasal saline and/or steroid, and some cases will require adenoid surgery.

Aspiration lung disease
We all cough as a protective mechanism when food or drink temporarily goes the wrong way into the respiratory passages, a process we call aspiration. If this happens frequently or routinely it will cause cough persistent cough, infection and even lasting lung damage. Aspiration can occur from the mouth above or from the stomach below.
 

• Gastrooesophageal reflux
  All babies reflux to some extent. Posseting, where a small amount of milk comes up during ‘winding’ after a feed, is a normal part of infancy. Where babies vomit frequently and more forcefully it can have health effects, with slow growth, abnormal feeding behaviours, and cough and infection.
  
  Reflux usually improves after infancy. Children will sometimes stop vomiting as they get older but still have so-called ‘silent’ reflux. Reflux causes respiratory symptoms by three mechanisms:

1. Aspiration - where stomach contents pass up through the gullet and spill into the lungs causing cough and sometimes wheeze or infection.
2. Reflex – where the rising stomach contents irritate the gullet and trigger the nerve pathways in the airways (the lungs and the stomach are formed from a common source and therefore share some nerve supply) to cause cough.
3. Nasal irritation – this is described above in Upper Airway Cough Syndrome.
   
   The evidence for treatment of reflux is conflicting but options include management of reflux triggers (such as cow’s milk allergy), anti-reflux medications, feeding with a tube into the lower intestine, and in extreme cases abdominal surgery.
   
   These children are often taken for asthmatic. This is because reflux cough is worse at night and with exercise, may associate with food allergy and wheeze, and is often worse with a viral respiratory infection. Because reflux can so closely mimic asthma, it is important to think of this when standard asthma treatment does not seem to work.

Unsafe swallow
Some children have reduced coordination of their swallowing muscles, allowing fluids passing near their voicebox to pass (be aspirated) into the lungs. Most children with this problem have other neurological problems but a minority may appear otherwise normal.

They will often eat solids and thicker liquids and purees without difficulty but will cough and splutter when given thin fluids like milk, juice or water. They can even aspirate on their own saliva.

These children need specialist care and may need thickened fluids to drink, medicine to thicken their salivary secretions, and in extreme cases may even need to be fed through a tube through the nose or abdominal wall into the stomach.

This article is NOT a replacement for seeking medical advice for your child. If you’re worried about your little one’s persistent cough and would like an expert opinion, either visit your GP or you can book an appointment to see Dr Nwokoro via his Top Doctors profile here.