Cockroach allergy: a study of its prevalence using skin tests with commercial extracts

Cockroaches have been increasingly recognized as an important source of indoor allergens. In this study we assessed the prevalence of cockroach sensitization among an outpatient population observed at our Department (155 patients with a mean age of 29 +/- 12 years), based on skin "prick" tests with four commercial cockroach extracts along with a common battery of standardized inhalant allergens. We found a positive wheal to at least one of these four extracts in 27 patients: 26 (96.2%) to Blatta orientalis, 10 (37%) both to Blatella germanica and 1 (3.7%) exclusively to Blatella germanica, with no significant concordance between them. We also observed in patients with cockroach positive skin "prick" test an association with atopy (p < 0.001) and with cutaneous reactivity to other indoor allergens, namely house dust mites (p = 0.02), danders (p = 0.01) and fungi (p = 0.01). These data confirm the higher risk of cockroach sensitization among the atopic population sensitized to indoor allergens. However, the heterogeneity of the positive cutaneous responses obtained in this study, possibly reflecting the incomplete standardization of cockroach extracts, questions the real prevalence and clinical significance of this particular sensitization.