Update on the prevalence of allergic sensitization to Russian thistle in South-eastern Ontario: retrospective chart review

Background

Russian thistle (RT) was identified as a potentially clinically significant allergen in phase three of the NHANES survey with over 15% of tested individuals having positive skin tests. Previously estimated prevalence rates of RT skin positivity in Kingston and surrounding catchment area were ~10%. RT was subsequently added to a standard allergen skin testing panel at Queen’s University’s Allergy clinic.

Objective

To determine the updated prevalence rate of skin test positivity to Russian Thistle in patients from Kingston and the Southeastern Ontario area, in an unselected patient population.

Methods

A retrospective chart review documented the rate of sensitization to RT extract (ALK-Abello). Only patients with appropriate histamine responses were included. Demographic data, presence of relevant clinical symptoms and skin test responses to RT and other cross-reacting allergens were recorded.

Results

609 charts were reviewed and 304 patients underwent skin testing for RT. Of these, 43 (13.8%) were positive. Of the test-positive cohort, 86% (37/43) had concomitant symptoms of allergic rhinitis/asthma. 41% (18/43) had symptoms that correlated with the predominant RT pollen season. 93% and 58% of these persons had concomitant positive skin tests to ragweed and birch; allergens with known cross-reactivity.

Conclusions

This suggests the prevalence of skin test positivity to Russian thistle in Kingston and surrounding area to be approximately 14%, with over 40% of patients reporting correlating symptoms. A higher degree of cross-reactivity with ragweed than previously known may exist. Continuing to include Russian thistle as part of routine allergen testing may further establish its clinical significance.