Allergy to cockroaches: challenges in diagnosis.

BACKGROUND: Blattella germanica and Periplaneta americana are the most common domestic species of cockroaches, found all over the world under favorable conditions. Allergen sensitivity can be detected through in vivo tests, such as skin prick tests (SPT) for immediate hypersensitivity and in vitro techniques, represented mainly by the sIgE determination. Nevertheless, there is no gold standard for the detection of hypersensitivity to cockroaches. This study aims to evaluate the agreement between skin prick test to different cockroach allergenic extracts with serum specific IgE determination in the diagnosis of cockroach allergy in asthmatic and non-asthmatic children. METHODS: A case-control study involving 74 asthmatic and 42 non-asthmatic children aged between 6 and 14 years was conducted in Recife, Brazil. All individuals were submitted to a skin prick test (SPT) with Dermatophagoides pteronyssinus, D. farinae, Blomia tropicalis (IPI-ASAC) and three different commercial cockroach extracts (Greer, Hollister-Stier, and IPI-ASAC Brasil) of B. germanica and P. americana, and to the quantification of total serum IgE and specific serum IgE to B. germanica and P. americana. RESULTS: The mean diameter of induced papule was considerably greater among the asthmatic patients when compared to non-asthmatic controls, regardless of the species or type of cockroach extract. The correlations between the various types of utilized extracts for the two species studied were not sufficiently strong. Hollister-Stier extract was the most sensible extract among asthmatics in this study for both B. germanica (54.1% [N = 40]) and P. americana (59.5% [N = 44]). A satisfactory correlation was found between the serum levels of specific IgE and total IgE for both species of cockroaches. The correlation of specific IgE serum level from each species with its respective SPT was not considered satisfactory. CONCLUSIONS: The weak correlation between the different extracts clearly indicates a need for standardization of the extracts for SPT for cockroach allergy diagnosis. According to this study, only a patient with high specific IgE serum levels and a positive SPT to a cockroach species should be truly classified as hypersensitive to B. germanica and/or P. americana.