Risk Factors for Childhood Asthma

Written by Dr Jan Vermeulen
© Allergy Society of South Africa & SACAWG

Introduction Wheezing in Infancy Risk Factors for Early Wheezing Risk Factors for Asthma 5 points to remember

 

 

Introduction

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• 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 are used to identify patients at risk, and to counsel individual patients.

 

Wheezing in Infancy

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• 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 present clinically very variably 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 outlook 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 evolve between 6 months and 3 years after birth. A small proportion present 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 any 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

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• ‘Small Airways’
  • congenital
  • smoking by mother during pregnancy and after birth
  • small-for-dates 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

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• 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 an offspring 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 show concordant asthma, that is if the one has it the other will or conversely if the one doesn’t have neither will the other

   

• Race: Although some studies suggest racial differences in prevalence of asthma, socio-economic and environmental differences must be taken into account when conclusions are made in this regard

   

• Urbanisation: socio-economic status: Asthma is more common in urban compared to rural communities and in more affluent than in poorer communities

   

• Air pollution: Although ambient air pollution has be implicated with increased lower respiratory tract illnesses, the same for asthma have not been shown on the other hand a close link with asthma attacks have been shown (see Indoor and Outdoor pollution and asthma)

   

• Cigarette smoking: Inhalation of cigarette smoke during pregnancy have linked with abnormal lung functions, airway hyper-reactivity and raised IgE levels in the newborn. Tobacco smoke is also an important trigger factor for asthma attacks

   

• Viral infections: Although viral infections are important triggers for asthma attacks, there is no conclusive evidence to indicate that early infancy viral lower respiratory tract illnesses lead to subsequent long term increase in airway responsiveness and asthma. Viral infections are a major cause of wheezing in early infancy, but proof of induction of the asthma state with typical airway inflammation as found in the known asthmatic is still lacking

   

• Allergy: A complex relationship exists between atopy and asthma. Umbilical cord blood IgE is a poor predictor of early infant wheezing, but if children with a raised cord blood IgE of >0,9 KU/l are followed to the age of 11 years, a five fold increase risk for asthma is found. Raised total IgE at age six months has an increased risk for atopy and asthma. Positive skin prick tests for inhalant allergens from three years onwards, evidence of atopic eczema and hay fever have a strong association with asthma. More than 80% of adults asthmatics have evidence of allergy to aero-allergens

   

• Food allergy: Many different foods and preservatives have been implicated in triggering asthma attacks. Inducing the asthma state by certain food substances have not been proven. 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

   

• Early allergen exposure: There is increasing evidence that early exposure to inhaled allergens (housedust mites, moulds, cats, "cockroach, pollen") in the genetically predisposed infant may lead to increased airway responsiveness and asthma. The increase of the prevalence of atopy when born in a specific month of the year can also be attributed to early exposure to the prevailing allergen at that specific time

   

• Airway responsiveness: "Current asthmatics" have increased airway responsiveness (AHR). Whether AHR precedes the development of the classic asthma state is not known. Until proven otherwise evidence of existing AHR should be seen as a important risk factor for asthma

   

• Psychological factors: Emotional factors play a major role in eliciting asthma attacks in the known asthmatic. No evidence exists that asthma can be induced by these factors. Certain psychological factors are seen as risk factors for eliciting severe and fatal 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 No cats in the house 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

Copyright: Allergy Society of South Africa.
Written by Dr Jan Vermeulen
Endorsed by ALLSA.

ALLSA P.O. Box 88 Observatory, 7935 Cape Town, R.S.A.

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