Cockroach sensitization mitigates allergic rhinoconjunctivitis symptom severity in patients allergic to house dust mites and pollen

Allergic rhinoconjunctivitis (AR) is the most common of IgE-mediated diseases, with some surveys indicating it affects as much as 40% of the surveyed population. The familiarity of its symptoms such as itching nose, eyes, or throat; watering eyes; compromised ability to smell; and sneezing underscores its ubiquity. Patients with the same sensitivities to various allergens have wide variation in the severity of their AR symptoms. This may be due to varying allergen-concentration in each patient environment. Alternatively, the sum total of the number and kinds of aeroallergens to which one is sensitive may determine symptom severity.

There is increasing evidence that supports the hygiene hypothesis as a basis for the development of allergy. This is to say that exposure early in life to certain allergens and bacteria helps to reduce AR symptoms and atopy in later life. He et al have thus investigated whether cockroach sensitization (C+) or its lack (C-), used as an indicator of childhood microbial exposure, affects AR symptom severity (J Allergy Clin Immunol 2015; 136(3):658-666).

The authors challenged two study groups and measured their total AR symptom scores (TSS). Group 1 was allergic to house dust mite (HDM). Sixty-seven percent of this group was also allergic to pollen and 43% were C+. Their TSS was recorded following challenge in both allergen challenge chamber (ACC) and natural settings. Group 2 was allergic to various pollens, and these participants recorded their TSS following ACC exposure that took place both during the natural pollination season and out of season.

The data showed participants in Group 1 who are sensitized to both HDM and pollen experience more severe AR symptoms than those who are only sensitized to HDM. However, C+ status associates with reduced symptoms, especially in those who are also allergic to pollen. Participants in Group 2 who are sensitized to pollen and are also C+ experience reduced AR symptoms, both during pollination season and out of season. These observations support the hygiene hypothesis and suggest that accounting for the overall aeroallergen sensitization status of participants in clinical trials could help mitigate confounding variables.