• wheat flour;
  • mite allergy

In 1996, we described two children in whom anaphylaxis occurred after the ingestion of a flour product contaminated with storage mites (1). We recently observed two similar cases due to mite-contaminated food; therefore, we are perhaps dealing with a medical problem that may occur more frequently than initially supposed.

A 9-year-old girl (patient 1) presented with chest tightness, hoarseness, sneezing, and streaming eyes immediately after eating homemade “okonomi-yaki”. Within 30 min, weakness, urticaria, wheezing, cyanosis, and loss of consciousness appeared. A 16-year-old boy (patient 2) noticed an itchy throat soon after eating homemade “okonomi-yaki”. In 60 min, skin flushing, wheezing, and dyspnea appeared. These patients had eaten stored but already opened flour-containing food products several times, but no adverse reaction had been observed.

The “okonomi-yaki” powder had been purchased 5 months previously in the case of patient 1 and 7 months previously in that of patient 2, had been opened once, and had then remained untouched in a cupboard until the day of the reaction. The powders were composed of flour, and dried scallop, bonito, and mackerel. A positive skin prick test reaction was observed in the patients with the remaining mixes. Skin prick test reactions to individual ingredients of the homemade “okonomi-yaki” and the unopened commercial mixes were negative, and no adverse reaction was observed in the oral provocation tests with the unopened mixes. Approximately 487 Tyrophagus putrescentiae mites were found in 100 mg of patient 1's mix and 198 Dermatophagoides farinae mites were counted in 100 mg of patient 2's mix. The result of CAP-RAST analysis of T. putrescentiae in the serum of patient 1 was 2.09 Ua/ml, and that ofD. farinae in the serum of patient 2 was 159.00 Ua/ml.

The study was performed to determine whether mite contamination could have occurred in the factory before the flour products had been packed or at home after the package had been opened. Twenty-eight “okonomi-yaki” packages from the factories were screened for mites. Since mature mites were not found in these samples, the samples were cultured at 25°C in a 75% humidified chamber for 4 weeks and then screened again for mites. Microscopic examination revealed no live or dead mites in these samples. The prevalence of mite contamination of unselected flour packages of the 16 brands marketed was also studied in 30 unrelated urban homes in Kumamoto city. All packages had been opened for periods ranging from 2 to 11 weeks, and all had been stored at room temperature. Mature mites were not found in any packages; therefore, the samples were cultured as described above and screened again for mites. Mites of four different species were found in four samples, as shown in Table 1.

Table 1.  Mite species in 30 unselected flour samples
SpeciesNo. of positive samples*Mites/g
  1. * A total of four samples (13%) analyzed contained mites. One sample contained three mite species.

T. putrescentiae22, 1
D. farinae211, 1012
Suidasia nesbitti18
Ascidae spp.12

An improperly sealed container would allow the entry of mites; therefore, mite-sensitive patients must be advised to store flour products in firmly sealed containers in the refrigerator to prevent mite invasion and proliferation.


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  2. Reference
  • 1
    Matsumoto T, Hisano T, Hamaguchi M & Miike T. Systemic anaphylaxis after eating storage mite-contaminated food. Int Arch Allergy Immunol 1996;109:197200.