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.