Risk Factors for Childhood Asthma
	Risk factors are determinants of the risk of developing childhood asthma and may increase or decrease the probability of an individual developing the disease. Risk factors can be: - personal characteristics inherited or acquired - environmental characteristics Information on risk factors is used to identify patients at risk, and to counsel individual patients.

Wheezing in infancy

• Wheezing during the first five years of life is extremely common as half of all children will experience at least one attack of wheezing during that time.
• This group of wheezing children have varying symptoms and not all will go on to develop asthma. It can be very difficult to identify the small percentage of early wheezers that will go on to develop asthma.
• There is now good evidence suggesting that wheezing with lower respiratory tract illnesses in the first three years of life has a good outcome and only about a third of these will still be wheezing at the age of nine years.
• On the other hand we also know that more or less 60% of asthma symptoms start between 6 months and 3 years after birth. A small proportion have symptoms prior to 6 months of age and the rest in later life.
• It is very important to identify the infant who has the predisposition for asthma. This can be very difficult at an early age and one has to rely on certain known risk factors for early wheezing and asthma to try and identify the child that will go on to develop classic asthma.

Risk factors for early wheezing

• 'Small Airways' caused by:
  • congenital (inherited factors)
  • smoking by mother during pregnancy and after birth
  • maternal viral illnesses during pregnancy
  • premature babies
• Broncho-pulmonary dysplasia
• Cystic fibrosis
• Congenital heart disease
• Congenital lung disease
• Increased risk in males
• Lower socio-economic status
• 'Creche child' Recurrent viral infections (coughs and colds) at creche
• Allergy plays a minor role where wheezing is the only presenting condition. It is more important where there is also hay fever and eczema

Risk factors for asthma

• Age and sex:
  • Asthma can develop at any age and has to be considered in every child presenting with wheezing
  • Males tend to predominate in the youngest age group, the sexes are equally represented from age 12-14, and females predominate through the rest of the age range.
• Family history: Asthma in a child is more likely if one parent has asthma with a risk of about 1 in 5, and even more likely if both parents have asthma with a risk of about 2 out of 3 of developing asthma. Identical twins are more likely than non-identical twins to both develop asthma.
• Race: Although some studies suggest racial differences in prevalence of asthma, socio-economic status: Asthma is more common in urban compared to rural communities and in more affluent than in poorer communities.
• Outdoor pollution
• Cigarette smoking: Inhalation of cigarette smoke during pregnancy has been linked with abnormal lung functions, airway hyper-reactivity and allergy in the newborn. Tobacco smoke is also an important trigger factor for asthma attacks.
• Viral infections: Viral infections are important triggers for asthma attacks.
• Allergy: More than 80% of adult asthmatics have evidence of allergy to aero-allergens.
• Food allergy: Food elimination diets have been shown to postpone the development of atopic eczema, urticaria and gastrointestinal tract allergic disease but not asthma and hay fever (see leaflet on "Food Allergy, Preservatives and Asthma").
• Early allergen exposure: There is increasing evidence that early exposure to inhaled allergens (house dust mites, moulds, cats, cockroach, pollen) in the genetically predisposed infant may lead to asthma. The increase in the prevalence of allergy when born in a specific month of the year can also be attributed to early exposure to the prevailing allergen at that specific time.
• Psychological factors: Emotional factors play a role in triggering asthma attacks in the known asthmatic. Certain psychological factors can be seen as risk factors for triggering asthma attacks:
  • Complicated interpersonal relationships.
  • Depression.
  • Separation in the family.
  • Loss in the family.
  • Feeling of helplessness.
  • Despair.

5 key points to remember

• Boys are at greater risk of asthma in childhood
• Do not smoke during pregnancy or expose your child to tobacco smoke after birth
• Breast feed if possible
• Cats in the home should be avoided
• The very young child with the predisposition to asthma should preferably be kept out of day care centres where there is an increased risk of viral infections.

Written by: Dr Jan Vermeulen