So advise researchers from several European countries following a huge international study. A major international study shows that the frequency of non-infectious rhinitis in children varies considerably among regions of the world. The project, which monitored some 54,000 children from 22 countries, also shows that only a small proportion of such rhinitis cases are caused by allergy.

According to the researchers who authored the study, to be published in the European Respiratory Journal (ERJ, the official publication of the European Respiratory Society), the role of other environmental factors has so far been underestimated, particularly in developing countries.

Frequent sneezing and a runny nose followed by a blocked nose turning runny again: such symptoms, where the child shows no signs of infection, are often considered to point to allergic rhinitis or "hay fever", particularly if the eyes are affected by conjunctivitis.

Yet there are few data to support this hypothesis, and a review of the recent literature indicates that only slightly over half of these cases are likely to be caused by atopic sensitisation.

So a team set out to assess the frequency and, in particular, the nature of paediatric rhinitis by geographical location, and to try to elucidate the mechanisms involved.

Gudrun Weinmayr (Institute of Epidemiology, Ulm University, Germany) and her colleagues in a number of countries studied over 54,000 children recruited in thirty centres, located in 22 countries spanning five continents. The subjects, aged between eight and twelve years old, were part of the International Study of Asthma and Allergy in Childhood (ISAAC) Phase Two. This follows Phase One from the mid-1990s, which first quantified paediatric asthma and allergy frequency and severity with questionnaires worldwide.

Questionnaires and skin prick tests

In Phase Two of ISAAC, the subjects' parents were asked to fill in a questionnaire that asked whether their children had suffered rhinitis symptoms during the previous twelve months, outside of any episodes of cold or flu infection. If they had, the parents were asked to specify whether the rhinitis had been accompanied by symptoms of conjunctivitis (watery or itchy eyes). In some countries with a high level of illiteracy, the questions were asked directly of the parents at a face-to-face interview.

In addition, most centres conducted skin prick tests to see whether the children had atopic sensitisation to common airborne allergens, both seasonal (predominantly tree and grass pollens) and perennial (house dust mites and cat dander). Furthermore, they were encouraged to test for other allergens on the basis of local geographical characteristics.

Record levels in Spain and China

The first result revealed in the ERJ by this international team is that the prevalence of both rhinoconjunctivitis and rhinitis without conjunctivitis varies strongly among countries, sometimes by up to fifteen times!

As Weinmayr points out, "the Ecuadorian province of Pichincha has 1.5% of children suffering from rhinitis and conjunctivitis, while the Spanish City district of Almeria has 24.5%". The UK is ranked midway, at 16.2%, close to France (14.6%), Sweden (13.8%) and Norway (12.6%).

Rhinitis without conjunctivitis is also found at its lowest levels in Pichincha province (2.7%), and the prevalence is ten times higher in the Chinese City district of Guangzhou (29.1%), which holds the record for this affliction.

Meanwhile, France (15.4%) and the Netherlands (15.3%) are close to the mid-point, as are the Hong Kong Special Administrative Region (15.2%) and Latvia (15.7%).

Complex association between atopy and rhinitis

With regard to allergies, the study once again shows that the prevalence of sensitisation to allergens (both seasonal and perennial) can vary considerably from one country to another. For example, the frequency of allergy to perennial allergens (mainly cat dander or house dust mites) varies from 1.4% in Ghana to over 45% in Hong Kong, and seasonal allergy (mainly due to pollen) affects only 0.1% of Ghanaian children but 25.8% of their Norwegian peers!

Interestingly, as Weinmayr comments, "we can see a strong association between rhinoconjunctivitis and sensitisation to seasonal or perennial allergens, but, for rhinitis without conjunctivitis, a link can be seen only with perennial allergens".

In other words, emphasise the ERJ article's authors, atopy is a major risk factor for rhinoconjunctivitis, but marginal for rhinitis without conjunctivitis.

Poorer countries have fewer allergic children

In parallel, the researchers note that the proportion of rhinitis cases with an allergic link is much higher in industrialised countries than in the developing world. Indeed, sensitisation to seasonal or perennial allergens explains 36% and 25%, respectively, of rhinoconjunctivitis cases in the wealthy countries, but only 12.6% and 1.3% in developing countries.

Yet, as Weinmayr admits, skin prick tests are not a perfect tool for measuring allergies of the nasal membrane, and other common allergies, such as food allergies, were not covered by the study.

Despite these limitations, however, this major international study sheds new light on non-infectious paediatric rhinitis and, importantly, underscores the poorly understood role of non-allergic factors in relation to this condition.

A number of these factors have already been suggested by earlier studies, including: parental smoking, particularly during pregnancy or breastfeeding; high birth weight; early introduction of solid foods; central heating; damp and mould in the home; and atmospheric pollution.

Now, the ERJ article's authors intend to determine the exact role played by these parameters in non-infectious paediatric rhinitis. In fact, Weinmayr reports that additional studies are already under way, again within the framework of ISAAC Phase Two. The results may be ready within the next two to three years.

TITLE OF THE ORIGINAL ARTICLE
International variation in prevalence of rhinitis and its relationship with sensitisation to perennial and seasonal allergens

The European Respiratory Journal

The European Respiratory Journal is the peer-reviewed scientific publication of the European Respiratory Society (more than 8,000 specialists in lung diseases and respiratory medicine in Europe, the United States and Australia).

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