Background:
Early wheezing induced by rhinovirus infection has been recognized as an important  risk 
factor  for  recurrent 
wheezing  and  asthma. 
Different  rhinovirus  species may also vary in their pathogenicity
to cause severe illness. Oral corticosteroid has been shown  to 
decrease  the  risk 
for  recurrent  wheezing 
episodes  after  the 
early  rhinovirus induced
wheezing. However, limited data exist on the first wheezing episode induced by rhinovirus.

Aims and
methods: The aim of this thesis was to study the virus etiology of the first wheezing
episode in small children by using PCR methods, as well as to specify the role of
rhinoviruses in wheezing. Rhinovirus species were analyzed using sequencing and
their association with atopic characteristics in small children was studied.
The one-year virus surveillance was conducted focusing on rhinoviruses. The
efficacy of oral corticosteroid, prednisolone, 
on  short-  and 
long-term  outcomes  was 
investigated  using  randomized controlled trial conducted in
children of 3-23 months of age.

Results:
Rhinovirus infection was found in 76% of children aged 3-23 months experiencing
their  first  wheezing 
episode.  Rhinovirus  induced 
first  wheezing  episode 
was  positively associated with
atopic characteristics and prolonged cough. Of the rhinovirus species, rhinovirus
C (58%) was the most common, followed by rhinovirus A (21%) and B (1.2%). Atopic
characteristics and illness severity factors were more common with rhinovirus A
and C than with other respiratory infections. Children with rhinovirus A or C
infection had an increased risk for recurrent wheezing episodes and the
initiation of regular controller medication 
for  asthma  symptoms. 
Children  with  high 
rhinovirus  load  benefitted 
from prednisolone in long- and short-term outcomes.

Conclusions:
Rhinovirus is a common pathogen in causing the first wheezing episodes in 3 -23
months old children. In wheezing children, the most important rhinovirus
species are A and C. These species are associated with a high recurrence rate.
Prednisolone might be effective in a subgroup of first-time wheezing children
with a high rhinovirus load.