Discussion
This study is one of the only few allergy birth cohort conducting in
developing Asian countries. The cumulative incidence of allergic
diseases in early childhood in our population was comparable to studies
in other countries 6,18,19. The percentage of multiple
allergic phenotypes was about the same rate as previous cross-sectional
studies 20,21. The contribution of both genetic and
early-life environmental factors for the risk of allergic diseases was
confirmed in our cohort. Maternal atopic disease, not paternal or
siblings, was found to increase risk of FA and the development of atopic
march. This suggests the prominent influence of maternal factors to
atopic outcome than the general family history of atopy.
Similar to several previous studies 22,23, our study
has shown that early antibiotic exposure in infants was a predisposing
factor of FA, wheezing and rhinitis. Antibiotics use in early life could
modify gut microflora and subsequently promotes Th2-predominant allergic
immune responses 24. Strong associations were also
found with multiple courses of antibiotic treatment. Families with high
socioeconomic status supposed to have more hygienic lifestyles, leading
to the less exposure to microorganisms and might relate to increase risk
of allergies and atopic march development. Pet owner, on the contrary,
protected for AD development in our population which is similar to the
previous findings in German birth cohort study 25.
Taken together, factors related to hygiene hypothesis seems to be
important on the development of allergy in our population.
Breastfeeding is the preferrable method for infant nutrition. However,
the protection against the development of allergic diseases is
inconclusive. Recent meta-analysis showed the protective effect of
prolonged breastfeeding on asthma in children aged 5–18 years, AR in
children up to 2 years of age, AD in children up to 2 years of age26. However, no association was found between
breastfeeding and FA 27. Our study found a negative
effect of prolonged exclusive breastfeeding on the development of FA.,
even though the influence of reverse causality cannot entirely be rule
out. As the parents with a family history of atopy might tend to
breastfed the infants, with the prospect that breastfeeding might
minimize the risk of allergy.
Other contributing factors to the development of allergic diseases such
as delivery mode, gender, parental education, having siblings, daycare
attendance, regular moisturizer used and smoke exposure3,4 were not significantly associated with allergic
manifestations in our cohort. Interestingly, our findings are in line
with some other studies such as GUSTO Singapore cohort28 and Avon Longitudinal Study of Parents and Children29, revealing that the cesarean section was not
associated with allergic diseases. This fact is opposed to the finding
of Norwegian birth cohort studies 30. These findings,
again, emphasized that data from other cohorts cannot directly be
adopted to developing Asian populations.
There are many strengths of our study. First, the subjects were
prospectively followed by allergy specialists. The diagnosis of allergy
was done using the International criteria and supported by positive
physical findings. Food allergy was confirmed by an oral food challenge
test. All these reasons made our data highly reliable. Recall bias is
minimized due to the frequent and regular visits. The limitation of our
study is the small number cohort from a single center, which recruited
only the healthy term subjects from the inner city area.
In conclusion, our study confirmed that allergic diseases are among the
most common health diseases in young children, even in developing Asian
country where the incidence of allergic diseases was previously
perceived to be low. Natural course, risk and protective factors of
allergic diseases and atopic march development were identified in the
prospective birth cohort manner. Identify the populations who are
at-risk and early modification of influence factors might promote
immunologic tolerance and prevent the development of atopic march.