Volumetric sampling of the air has repeatedly shown that concentrations of mite allergens are generally very low to undetectable. The International Association of Allergology and Clinical Immunology (IAACI) has recommended sampling settled dust to evaluate exposure to dust mite allergens. The ACGIH has stated that it is important to sample multiple indoor locations to obtain a reasonable determination of mite prevalence. Dust samples for dust mite allergens can be collected using a dust cassette or by using a specially designed dust trap attached to a vacuum cleaner. A filter or a 9 square inch bed linen can otherwise be placed between the hose and the attachment of vacuum cleaner to collect the dust. Keep samples cool (place in refrigerator until shipped to the lab) and ship the samples to the laboratory for allergen testing using a cold pack or in a cooler. By not cooling the samples, the dust mites present in the sample may grow in numbers and produce more fecal pellets than actually present at the time of sampling and so may produce inaccurate test results.
Detection and measurement of dust-mite antigen (allergen) is performed using an immunoassay. An Enzyme Linked Immuno-Sorbant Assay (ELISA) is used to quantify mite allergen concentration in dust samples. Using monoclonal antibodies specific for dust mite allergens Der p1, Der f1 and mite group 2, the level of dust mite allergens present in the sample are analyzed. The level of dust mite allergen present in the sample is reported in micrograms per gram (µg/g) of dust.
The IAACI proposed dust-mite allergen limits for residential dwellings considers exposure to dust containing 2µg/g of mite allergen to increase the risk of dust-mite sensitization as well as the development of asthma and bronchial hyperreactivity in affected persons. Exposure to dust containing 10µg/g of mite allergen represents a higher risk level and an increased chance of acute asthma attacks.
Prevention and Control
A few suggestions on how to minimize mite reproduction and allergen release following confirmation that dust mites are present indoors are as follows:
- Where mites may breed, maintain relative humidity below 50%.
- Vacuum regularly and discard vacuum bags immediately.
- Wash bedding every week in hot water (54°C).
- Replace carpet with hard flooring if possible
- Use allergen free mattress and pillow covers to minimize contact with the dust mites.
- Keep upholstered furniture to a minimum.
- Use HEPA air filters to keep mite particles out of air. (Note that since mite particles settle rapidly due to their relatively large size, this may be of limited value.)
- Minimize the use of curtains or drapes by using shades.
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