Introduction
Wheezing related to lower respiratory tract infections (LRTI) is common
in infancy, with approximately one in every three children experiencing
at least one wheezing episode during the first three years of
life.1,2 The first wheezing episode in infants aged
under 24 months has traditionally been called bronchiolitis, although
the age limit of bronchiolitis in most European countries is 12
months.3 Respiratory syncytial virus (RSV) is the most
common cause of bronchiolitis in wheezing infants younger than 12
months, whereas rhinovirus is common in those wheezing child aged 12-24
months.3
Previous birth cohort and post-bronchiolitis studies reported that
bronchiolitis and wheezing in early childhood may have long-term effects
on respiratory health.4,5 Wheezing and asthma
symptoms, although common after bronchiolitis at preschool age, usually
improve at school age. However, after puberty, the symptoms may recur,
even in those without any symptom recurrence after
bronchiolitis.4 Long-term follow-up studies
demonstrated an increased risk of asthma and impaired lung function
continuing until adulthood after viral wheezing in early
childhood.6-9
The factors that influence the development of asthma are complex and
remain, despite of active research, poorly
understood.10 A familial history of asthma, especially
in the mother, exposure to tobacco smoke in infancy and the presence of
atopic dermatitis in early life were found to be common risk factors for
asthma after wheezing in the first two years of life in both birth
cohort and post-bronchiolitis studies.4,11 In young
children, specific laboratory markers, such as eosinophilia and a high
immunoglobulin E (IgE) level, as well as early-life sensitization to
airborne allergens confirmed by skin prick tests (SPTs) or by measuring
specific IgE to airborne allergens in serum samples, have been
documented as predictors of asthma in later life in hospital-based
follow-up studies.12
At preschool age, an asthma diagnosis is usually based on typical
symptoms and asthma-predictive risk factors.13Therefore, a diagnosis of asthma in early childhood may be more
uncertain than in later years (i.e. school age) when airflow obstruction
can be confirmed by lung function tests.13
We followed up a cohort of 100 children aged less than 24 months at the
time of hospitalization for viral wheezing episodes in Kuopio University
Children’s Hospital, Finland in 1992–1993 14 to early
adulthood. The aim of this study
was to evaluate early childhood risk factors for asthma in later life
(i.e. aged 17–20 years) in this prospectively followed cohort. An
additional aim was to describe the evolution on asthma from infancy
through to early adulthood after hospitalization for viral wheezing in
early childhood.