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Wise et al.

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comparing AR prevalence rates between locations is the difference in methods used to recruit participants to studies and differences in assessing the presence of disease. For example, Bauchau and Durham 9 diagnosed Belgian patients via serological IgE testing after a positive telephone screen and reported that Belgium had an AR prevalence of 28.5% (the highest of the European countries evaluated). In contrast, Bousquet et al. 456 skin-tested a random sample of Belgian subjects and reported a positive rate in Belgium of 16.4% (one of the lowest of 15 countries examined). There have been major international efforts to compare variations in the national prevalence of AR using standardized methods (ie, ECRHS and ISAAC). These studies show marked geographic variation of “hay fever or nasal allergies” (adults) or “a problem with sneezing, or a runny, or a blocked nose when you DID NOT have a cold or the flu that was accompanied by itchy-watery eyes?” (children). A higher prevalence of these responses is seen in people living in “English-speaking” countries (eg, UK, Australia, New Zealand), a lower prevalence in Eastern Europe than in Western Europe, and a diagnosis of AR is more frequently seen in countries with higher asthma rates and sensitization to seasonal allergens. 455,475 Because these studies have evaluated national rates based on only one or a few centers within each country, substantial intracountry variation may have been overlooked. In understanding the effects of geographic location, differentiating between seasonal and perennial AR is an important consideration not examined in the ECRHS or ISAAC studies. Smaller studies over more limited geographic regions that examined PAR suggest increased sensitivity rates in urban settings and colder climates. 476-479 Several hypotheses have been put forward for these observed differences. Li et al. 477 theorized that urban dwellers participate in more indoor activities compared to their rural counterparts, amplifying their exposure to HDM, and possibly leading to increased sensitization to these perennial allergens. Additionally, some reports suggest that exposure to urban pollutants may be associated with increased risk for developing AR in children. 476 Latitude may also play a role with regard to PAR. For example, the prevalence of persistent AR was found to be higher in both Northern Europe and Northern China compared to their southern counterparts. 9,477 Latitude may also be an important determinant of SAR. Allergenic plant species may have a propensity for growing in certain geographic locations, and pollen concentrations of various species depend on the climate conditions of the area. Colder climates present at northern latitudes tend toward shorter growing seasons, and many allergenic species do not thrive in extreme northern climates. For instance, grass pollen, which is found across Europe, causes wide variations in atopic sensitizations across regions with different climates. 480 Additionally, this increased environmental exposure has been shown to affect development of AR and patient symptoms of atopic nasal diseases. 481,482 Overall, improved knowledge of the prevalence and seasonal variations in AR based on geographic location is important in that it allows patients to anticipate and better manage their symptoms through avoidance techniques and preemptive use of pharmacologic therapies. 480,482 Currently, prevalence data do not fully address the different phenotypes of AR and further study is needed to expand epidemiologic understanding of this disease.

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Int Forum Allergy Rhinol . Author manuscript; available in PMC 2020 June 10.