Environmental Engineering Reference
In-Depth Information
measures used to reduce exposures are case specific; i.e., unique control
measures are used to control individual allergen sources.
The probability that an individual will develop allergy
or asthma from exposures to dust mite antigens (allergens) depends on his/her
genetic predisposition and dust mite populations that produce significant
levels of mite antigens. Dust mites must have a suitable environment to live
and multiply. Primary environmental requirements are a source of human skin
scales and elevated relative humidity. These are facilitated by high building
moisture conditions, carpeted flooring, and bedding. A number of control
measures have been evaluated to control exposures to dust mite antigens.
a.
Dust mites.
i. Dust control. Many allergists advise their patients to use dust con-
trol measures. These include enclosing mattress tops and sides with a plastic
cover; thoroughly vacuuming (with a HEPA vacuum) mattresses, pillows,
and the base of the bed; daily damp dusting the plastic mattress cover; and
weekly changing and washing of pillow cases, sheets, and underblankets.
These practices are designed to reduce dust mite populations, allergen pro-
duction, allergen exposure, and allergen-transporting dust. The plastic sheet-
ing prevents allergen-containing fine dust particles from being embedded
in the mattress and facilitates vacuuming. Other dust control measures
include frequent vacuuming of textile floors and soft furnishings.
Though physicians recommend the use of dust control measures, studies
evaluating their effectiveness in reducing dust mite allergens and asthmatic
and allergic symptoms have shown mixed results, varying from completely
ineffective to highly effective. The reason for such differences is likely due
to differences in patient compliance with dust control measures. Good com-
pliance typically occurs with procedures that are easy (bedding changes)
and poor compliance with those that are more demanding (frequent vacu-
uming). Vacuuming must be done with a HEPA vacuum, as conventional
devices increase airborne dust concentrations and aggravate symptoms.
ii. Climate control. Dust mites obtain their water requirements from
the atmosphere. They require a minimum relative humidity (R.H.) of 70%.
Humidity requirements to sustain dust mite population growth are achieved
by a combination of elevated indoor humidity and higher humidity in
microenvironments associated with textile floor coverings. Therefore, the
control of dust mite populations, and, indirectly, mite allergen levels, can be
achieved by various climate control measures. These include building on a
dry site, dehumidifying to R.H. <50%, air conditioning during humid
months, and removing carpeting from bedroom flooring of mite-sensitive
individuals. These control measures have been shown to significantly reduce
dust mite populations and allergen exposure potential.
iii. Biocides. Dust mite populations can be controlled effectively by
application of aqueous and powdered acaricides to mite-infested surfaces
(e.g., bedding, carpeting, and upholstery). Mite acaricides include formula-
