This is the first study to present estimates of the prevalence of allergic disorders in the two communities of Cyprus that have been living apart on either side of the division line on the island for nearly 40 years. In the G/C community, prevalence of current wheeze in 7–8 year-old children assessed with the use of ISAAC questionnaire was 8.7% in 2008, demonstrating a rising trend from the previous recorded estimate of 6.9% in 2000–01 . In the T/C community, there is currently no evidence regarding the temporal prevalence trends of allergic conditions in childhood. The literature is restricted to a single study, performed in 1999, when prevalence of current wheeze among children aged 6–14 years was estimated at 4.8% . Although the ISAAC protocol was also employed in this study, no direct comparisons can be made with our findings due to the different age spectrum of the study populations.
The main strength of our report is the use of the same standardized protocol to study concurrently childhood allergies in large population samples from two communities that live apart on a small divided island. However, due to the cross-sectional nature of the study and absence of objective markers of atopy no causative inferences can be made between the identified risk factors and study outcomes. The response rate among the G/C community was lower than the one in the T/C community, possibly as a result of the steady rise in the number of surveys performed in G/C schools in the last decade. Nevertheless, we do not think that this has compromised the representativeness of the G/C sample since the socio-demographic characteristics of the participants compare very favorably with the profile recorded in other epidemiological studies performed at a similar time in this population with much higher response rates; details of this, and other sensitivity analyses performed to assess the possible magnitude of selection bias in the G/C sample were published in a previous report . Even though the socio-demographic composition of the G/C sample supports its representativeness, we cannot entirely rule out that the findings are not affected by the lower participation among G/C children. Differential selection bias (whereby allergic G/C children were less likely to participate in the study than T/C allergic children) would result in an underestimation of the true prevalence in the G/C community. However, it is more likely that affected children from both communities were probably more likely to have an incentive to participate in the survey. In that case, the lower response among the G/C would have led to an overestimation of the prevalence rates, and hence, differences in the prevalence of symptoms between the two communities may be even larger than those observed.
The fact that the T/C community presumably leads a less “westernized” lifestyle than the G/C community, made us speculate that the prevalence of allergies may be lower amongst T/C children. Refuting our original hypothesis, our results showed that the prevalence of allergic disorders, with the exception of eczema, was consistently lower in the G/C community, which can not accounted for by the socio-demographic and lifestyle characteristics of the participants.
In contrast, lower prevalence of self-reported family history of allergies was found in the T/C community, suggesting a paradox of a community with lower prevalence of family history of allergy among parents but increased risk of allergies among children. Although such a possibility can not be excluded, it is generally accepted that parental allergy is associated with increased risk of allergies in the offspring [17, 18]. It is likely that allergic diseases were underdiagnosed among family members of the T/C participants. Perhaps, this may be the consequence of lower access of the previous generation of T/C to specialized primary care and, as a result, under-detection of allergic diseases or, alternatively, it may be the result of using other diagnostic terms for asthma, eczema or rhinoconjuctivitis in the T/C community at the time. Such a possibility can not be ruled out as in a recent national multicenter study for allergic diseases in schoolchildren in Turkey  there was a substantial discrepancy in prevalence between lifetime wheezing ( range 31–37,9% ) and lifetime asthma diagnosed by physician (1.8-6.3%). Despite the possible misclassification in the T/C community, there was no statistical evidence of a weaker association between self-reported family history of allergy and symptoms in the T/C community. We believe that the possible discrepancies in diagnostic labeling between the two communities in Cyprus do not affect the estimates of our study on the prevalence of allergic disorders as we focused on answers to questions of the ISAAC questionnaire referring on symptoms and not on diagnostic labeling.
In contrast to the pattern observed in the case of asthma and hay fever, eczema was more frequent in the G/C community. Although in most European countries high prevalence of eczema is observed along with high prevalence of wheezing [20, 21], this is not always the case. In Sweden for instance, the prevalence of reported eczema  is considered among the highest in the world (35,7%) whereas the prevalence of asthma  is rather moderate (8%).
Our prevalence estimates are generally within the range observed in other countries of the region such as Greece  and Turkey  The prevalence of current wheeze in Greece ranged from 5.7% to 8.7% in 2001  while in Turkey in 2005 estimates were as high as 14.1% to 22.6% , despite the fact that westernized lifestyle is more prominent in Greece. At least with respects to wheeze, estimates from Turkey appear even higher than the prevalence observed among T/C children in our study. The interaction of genetic predisposition with environmental exposures has been shown to influence immune responses relating to asthma pathogenesis and might be of particular importance especially in early life [22, 23]. Perhaps genetic susceptibility or unknown environmental risk factors underlie the observed difference between the Greek and Turkish populations and might also be responsible for the observed higher prevalence of atopic symptoms in the T/C children in our study.
Differences between the younger and older age groups in terms of identified risk factors were mainly observed with regards to (a) the association with number of siblings (i.e. restricted to the younger children), (b) area of residence (with lower prevalence of wheeze in rural areas among older children only) and (c) exposure to tobacco smoke (with higher risk of all study outcomes in older children but only rhinoconjunctivitis).
A higher number of siblings seems to protect the younger children against wheezing and eczema but no similar effect was observed in the older group. In contrast, family size was not associated with the risk for rhinoconjuctivitis in the younger group, but increased the risk by 40% in the older group. Most epidemiological studies reported an inverse association between number of siblings and eczema, asthma and more consistently with hay fever [24, 25]. However, Matheson et al.  showed that number of siblings were important predictors only for the development of early onset allergic rhinitis (<7 years of age) but not for later onset allergic rhinitis perhaps explaining the lack of inverse associations in the older children.
Other hygiene hypothesis factors such as early nursery attendance and contact with farm animals at home were not associated with any allergic disorder although the latter could be attributed to the small number of families (260/10156) who kept farm animals at home. Thus, the protective effect for asthma conferred in older children residing in rural areas cannot be attributed to exposure to farm animals but it is more likely reflecting adverse environmental exposures in children residing in urban areas instead, such as high traffic-related emissions, or the generally more westernized lifestyle of the urban population. It is interesting that no similar urban–rural differences were observed in the younger age-group. A recent study by Kolokotroni et al.  showed that, at least in G/C community, there was an increase in the prevalence of wheeze and hay fever between 2000 and 2008 that occurred primarily in the rural rather than the urban areas. It is possible that environmental and lifestyle changes experienced by both communities in the past decade might have led to increasing “urbanization” of rural areas affecting primarily the younger cohort of children. Similarly, in the case of older children the prevailing environmental and lifestyle factors in the rural areas during the first years of their life might have had a protective effect that is extended until adolescence.
In line with the evidence provided by Bruke et al.  in a recent meta-analysis we found strong association of wheeze and maternal smoking during pregnancy in the younger children for whom information was available. Exposure to tobacco smoke at home was also associated with at almost 60% increase in the risk of wheezing, nearly doubling the risk for eczema and three times for rhinoconjuctivitis, but only among older children. In younger children, the effect was apparent only for rhinoconjunctivitis. A meta-regression study found that older children exposed to second hand tobacco smoke were more likely than younger children to develop asthma, hypothesizing that the risk increases in later childhood as a result of a longer exposure to smoke . Interestingly, after we stratified the analysis by community, we also observed a significant risk of wheezing with passive exposure to tobacco smoke amongst the younger T/C, but not in the G/C children. This finding may reflect a changing pattern in smoking habits at home amongst the younger generation of parents in the G/C but not in the T/C community (i.e. outdoors instead of indoors).
Active smoking among the 13–14 year olds was not common as it was reported in less than 2% in both communities. Nevertheless, active smoking in our study was a significant risk factor for wheeze and severity of asthma as well as for rhinoconjuctivitis, even after adjusting for passive household tobacco exposure, consistent with the findings of previous studies [29–31].
Finally, we did not observe any clear socio-economic gradient in allergic symptoms, at least when examining parental education as a surrogate measure of socioeconomic status. Current evidence on the impact of socio-economic status on development of allergies is rather conflicting [32–36] with some studies indicating a social gradient for allergic disorders in childhood [33, 35] and others not .