Dust mite infestation in cooking flour: experimental observations and practical recommendations

Background: The first documented case of oral mite anaphylaxis has recently been reported in Thailand, with mites possibly originating from cooking flour.  Objective: Our study was designed to assess the effects of cooking flours enhancement and storage conditions on mite proliferation and to provide practical recommendations to prevent mite anaphylaxis. . Methods: In a factorial experiment, six commercial brands of cooking flours were selected and either inoculated or set free of mites and stored in one of the four containers chosen for the study: original package, plastic bag, plastic box and glass bottle. The resulting experimental units where then stored at either room temperature or in a refrigerator (+4C). In order to determine levels of Der f 1 allergen, 0.1 gram of flour was sampled from each experimental unit and tested by ELISA. Sampling was carried out immediately after inoculation and subsequently at week 2, 4, 6, 8, 10, 12, 16 and 20. Results: Levels of Der f 1 allergen in the inoculated samples increased significantly in all conditions 6 weeks after inoculation ( p <0.001) and reached the highest levels at week 8. While experimental units left at room temperature  showed higher levels of mite growth ( p <0.001), no statistical differences were found among types of containers. The highest amount of Der f 1 was observed for Gogi, followed by Gold Label, tempura flour, corn flour, wheat flour and tapioca starch, respectively ( p <0.01). Conclusions: In the context of our experiment, mites preferably grew in cooking flours containing high amounts of wheat at room temperature, particularly after 8 week of storage. According to our results, we thus advise to keep household cooking flour refrigerated and while the type of container does not matter, storage should not exceed 20 weeks.