Severity of bronchiolitis and future risk of childhood asthma

This study was carried out to determine whether a relationship exists between the severity of infant bronchiolitis and the risk of early childhood asthma (ECA) and its morbidity.

This was a population-based retrospective birth cohort study, including more than 90,000 term, normal birthweight infants enrolled in the TennCare program within the fi rst month of life, from 1995–2000. Eligible children were continuously enrolled in TennCare during the first year of life, during which healthcare visits for bronchiolitis were captured, and between 3.5–5.5 years of age, during which early childhood asthma (ECA) was defi ned. Children with an International Statistical Classifi cation of Diseases and Related Health Problems (ICD)-9 diagnosis code of 493 (asthma) for inpatients, other hospital care (23-h observation), emergency dept (ED) visit or two outpatient physician visit claims and two prescriptions for any short-acting -aganist within 12-month period or a prescription for other asthma medications (inhaled steroids, long-acting -aganist) were considered to have ECA. The main predictor variable was severity of bronchiolitis during infancy defi ned by the type of bronchiolitis healthcare visit. Multivariable logistic regression models were used to measure the relative adjusted odds of asthma during early childhood associated with infant bronchiolitis  severity.

Results

90,341 term healthy children were included in this cohort study. 49% were female; 56% were white, 39% were black and 2% were Hispanic (other/unknown 3%). The median gestational age was 40 weeks and the median birth weight was 3,289 g. 26% of children had mothers who smoked during pregnancy. In total, 11% of all children were given a diagnosis of ECA between age 4–5.5 years. 18% of children had at least one visit for bronchiolitis: among them, 9% were seen asoutpatients, 4% in the ED and 5% were hospitalised; these children accounted for 31% of children with ECA. The proportion of children with ECA, stratifi ed by severity of infant bronchiolitis, were as follows: no visit 9%, outpatient 16%, ED 19% and hospitalisation 22%, with a p>0.001 among classes. The odd ratios (ORs) for asthma between age 4–5.5 years were 1.86 (95% confi dence interval (CI) 1.74–1.99), 2.41 (95% CI 2.21–2.62) and 2.82 (95% CI 2.61–3.03) in the outpatient, ED and hospitalisation groups, respectively. Among children with both a maternal history of asthma and an infant hospitalisation for bronchiolitis, the odds of ECA were 4.18 times those of children without any either risk factor. Risk factors that increased the odds of ECA were: having a mother who did not smoke during pregnancy, having ≥1 siblings, being black, living in an urban region of Tennessee (USA). Regarding the relationship between severity of bronchiolitis and ECA morbidity, 19% (1,455 out of 7,607) of children, who met the defi nition of asthma between age 3.5–4.5 years, met the criteria for an asthma-specifi c morbidity event (≥1 asthma hospitalisation, ED visit or prescription for oral corticosteroids during the follow- up year from age 4.5–5.5 years). These 7,607children had an OR of having an asthmaspecifi c morbidity event of 18% if they had no visit, 17% if they had an outpatient visit, 22% if they had an ED visit and 24% if they had a hospitalization (p<0.001).

Conclusions

The authors found a positive relationship between severity of bronchiolitis and both the risk and morbidity of early childhood asthma. Moreover, the phenotype of asthma after infant bronchiolitis accounts for nearly one-third of ECA diagnoses.

(Carroll KN, Wu P, Gebretsadik T, et al. The severity-dependent relationship of infant bronchiolitis on the risk and morbidity of early childhood asthma. J Allergy Clin Immunol 2009; 123: 1055–1061).

Message: Bronchiolitis is associated with risk and morbidity of early childhood asthma.

Comment:

This is the first study that has tried to demonstrate a relationship between the severity of infant bronchiolitis and the risk of both developing ECA and increased asthma morbidity. As the authors themselves underline, it is not known whether children with bronchiolitis have an intrinsic predisposition to develop ECA or whether, as other studies suggest [1–3], respiratory viruses are partially responsible for the subsequent development of asthma, due to their infl ammatory effects on airways, especially during infancy [4]. Furthermore, the relationship between the severity of bronchiolitis and the risk of asthma is an interesting but challenging concept. In this study, the authors demonstrated a linear and statistically significant relationship, but other studies showed confl icting results [5]. Some considerations are relevant, besides those pointed out by the authors themselves:

1) the definitions used to identify asthma and the severity of bronchiolitis are questionable – the authors studied asthma diagnoses after age 4 years to exclude “transient early wheezers”, choosing this limit based on the study by MARTINEZ et al. [6]. This limit is applicable to the vast majority of children, but some children could “transiently” wheeze also after 4 years of age and then not develop asthma;

2) diagnosing bronchiolitis and asthma based on ICD-9 code in discharge fi elds or on type of prescriptions could lead to errors – there could be some children with transient wheezing misdiagnosed as having asthma and asymptomatic children who have not required any visit or treatment;

3) furthermore, diagnosing asthma based on only two prescriptions for any short-acting-agonist or a prescription for inhaled corticosteroids could increase the percentage of children with asthma, since these medications (especially inhaled steroids) could be prescribed also for persistent cough or virus-induced cough;

4) there are also other “predisposing” factors to asthma, which are not included in the analysis, such as other atopic diseases (atopic dermatitis, food allergy), other blood parameters (specifi c immunoglobulin E, eosinophilia) or paternal/sibling asthma;

5) these results were obtained from a “selected” population of children, with a state-based health insurance. As the authors themselves underline, children could access the ED or could be hospitalized because of social/familial impairments, and not because of severity of bronchiolitis.

-F. Saretta, M. Canciani, Udine, Italy In Breathe  September 2009; 6: 71-2.

References

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