medwireNews: Risk factors for asthma subtypes and markers of asthma control vary with age up to preadolescence, a study of a Swedish birth cohort has revealed.
“There is limited understanding about risk factors for asthma and few studies have presented an overall picture of factors associated with asthma subtypes in schoolchildren”, the researchers write in Pediatric Allergy and Immunology.
They followed up a birth cohort of 3015 infants in a district of Stockholm, administering parental questionnaires at birth and at 1, 2, 4, 8 and 12 years after enrolment.
Children were considered to have asthma at 4, 8 and 12 years if they fulfilled at least two of the following criteria: wheeze in the 12 months prior to assessment; intake of asthma medication in the past 12 months; and a doctor’s diagnosis of asthma.
Asthma was considered to be transient, in children who fulfilled the criteria at 4 and 8 but not at 12 years; late onset, in children who only fulfilled the criteria at 12 years; or persistent, in those who fulfilled the criteria at all three time points.
At both 8 and 12 years of age, 11% of children were considered to have asthma (representing 323 and 329 children, respectively). Of those with asthma at 8 years old, 22% had transient asthma, which suggests that previous definitions of transient asthma as lasting up to 3 to 5 years of age may need to be extended, the researchers note.
There were no discerning differences in risk factors between children with transient asthma and 2336 non-asthmatic children.
But the researchers found that preterm birth and being overweight at 8 years of age (>85th percentile) both increased the risk of late-onset asthma at 12 years old, with adjusted odds ratios (ORs) of 2.54 and 1.78, respectively. Other risk factors for this asthma subtype included allergen sensitisation (OR=4.23) and rhinitis (OR=2.30) at 8 years of age.
Rhinitis and allergen sensitisation when aged 8 years also increased the risk of persistent asthma, as did being male, being exposed to tobacco as an infant and having a family history of allergic disease. In addition, children with persistent asthma were found to have significantly reduced lung function at 8 years old and more eczema than non-asthmatics.
Lead author Björn Nordlund (Astrid Lindgren Children’s Hospital) and colleagues say: “We found that allergic sensitization and rhinitis at 8 years were associated with persistent asthma, and they were also comorbidities preceding the development of late-onset asthma, which could be a sign of the atopic march, or an indication that rhinitis is a predictor for the subsequent onset of wheeze.”
Measures of impaired asthma control, specifically the prevalence of nocturnal asthma, acute healthcare utilisation and frequent wheeze, declined in children with persistent asthma between the ages of 8 and 12 years. Nordlund et al suggest that this may be due to the smaller airways of young children.
“Awareness of age-related differences in schoolchildren’s asthma control has important clinical implications for management and treatment, as well as for assessment of asthma control in relation to clinical research”, they conclude.
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013
By Afsaneh Gray, medwireNews Reporter