The link between the upper and the lower respiratory tracts has been consistently established in the past few years. Epidemiological, functional and immunological evidence have led to the unifying hypothesis of upper and lower airways (united airways disease) (5). Allergic conjunctivitis may be part of this entity, but has not been specifically evaluated as co-morbidity. Little focus has been set on the impact of allergic conjunctivitis as co-morbidity to asthma and rhinitis in atopic patients (1).
We determined the prevalence of allergic rhinoconjunctivitis and its relationship with other allergic diseases in a cross-sectional study of individuals aged 13–14 years in public and private schools, in Curitiba. The procedures followed ISAAC methodology (2, 3). Briefly, the participants were randomly selected from schools, according to data provided by the State Education Department. The ISAAC written questionnaire had been previously translated to Portuguese (Brazilian culture), translated back to English and validated. The written questionnaire was self-completed by the students in classrooms. Symptom prevalence was calculated by dividing the number of positive responses to each question by the number of completed questionnaires. The relationship of rhinitis with wheezing and eczema was targeted for by the question referring ocular allergic symptoms (itchy-watery eyes) in addition to its association with nasal symptoms during the last 12 months without upper airway infection (nasal pruritus, sneezing and rhinorrhoea) (2, 3).
Three thousand six hundred and twenty-nine subjects answered the written questionnaire (96% returning rate), of whom 625 (17%) presented nasal and ocular symptoms. The frequency of allergic conjunctivitis was similar between boys (48%) and girls (52%). All of the subjects with rhinitic symptoms also presented with ocular symptoms. Among patients with allergic rhinoconjunctivitis, 34% had wheezing during the last 12 months and 7% had eczema (see Fig. 1).
Seasonal rhinitis and rhinoconjunctivitis in the absence of other signs of respiratory infection are strong indicators of IgE-mediated allergy. Rhinitis as a single entity is less specific than rhinoconjunctivitis, as in addition to allergy it is often triggered by infections, air quality and physical stimuli. This may explain the divergent outcomes for rhinitis when compared with rhinoconjunctivitis. However, the prevalence of symptoms in this study was the same. It is possible that in some subjects naso-ocular reflex contributed to the ocular symptoms associated with allergic rhinitis (4). The prevalence of symptoms of allergic rhinitis and conjunctivitis was 17% in this population. In the USA, ocular allergies are estimated to affect 15–20% of the general population (5).
Response to a written questionnaire followed by a subsequent interview of 396 Swedish schoolchildren aged 12–13 years estimated the cumulative prevalence of allergic conjunctivitis of 19.1%. The prevalence of the combination of allergic conjunctivitis and allergic rhinitis was 17.6% suggesting a co-morbidity of 92% (6).
Patients with allergic rhinitis frequently present with symptoms of allergic conjunctivitis. However, terms such as hay fever or allergic rhinoconjunctivitis have been used and prevalence studies have not been specifically addressed to allergic conjunctivitis. Children with allergic conjunctivitis had other diagnosis in a secondary paediatric outpatient clinic: 97% had allergic rhinitis (7). From a pathophysiological point of view, it may be important to assess the relevance of allergic conjunctivitis for the ‘one airway, one disease’ concept (7). The prevalence of allergic conjunctivitis is high, as well as its association with other atopic diseases, commonly with allergic rhinitis. Focusing on conjunctivitis could improve the diagnosis of allergic rhinitis. In the ISAAC study, we missed the opportunity to assess the prevalence of conjunctivitis symptoms. If validated questions for ocular symptoms had been included, it could have facilitated the identification of the prevalence of conjunctivitis and its relationship with other allergic diseases.