Washing Dusting Dry cleaning Vacuuming

Public Health Significance of Urban Pests 107 HDMs. However, the mites were soaked in the solutions for a considerable period of time, which does not necessarily reflect real life conditions, where mites may only be exposed to the disinfectants for a short period of time or else come into contact with them after the water has evaporated.

3.3.4.2. Washing

HDM allergens are extremely soluble in water, enabling them to be removed from items during washing. Watanabe and colleagues 1995 found that washing blankets with a hot 55ºC soap solution reduced Der p 1 levels by an average of 97 and Der p 2 levels by an average of 91. McDonald Tovey 1992 found washing bedding at 55ºC killed all mites present, while reducing the temperature to 50ºC killed only half of them. Most was- hing machines have washing cycles at 40ºC, 60ºC and 90ºC; temperatures of 60ºC or more are therefore recommended. If the bedding has to be washed at low temperatures, it is possible to add special products to the wash to kill the mites McDonald Tovey, 1993; Bischoff et al., 1998. In addition to bedding, clothing can also be a source of allergens Tovey, Mahmic McDonald, 1995.

3.3.4.3. Dusting

Dusting is an effective method of removing house dust and therefore allergens; damp dusting is particularly effective. No specific studies have been reported, although Tovey 1992 found that a vigorous cleaning regime in addition to a number of other measures generally is important in the success of clinical trials.

3.3.4.4. Dry cleaning

Kniest, Liebenberg Bischoff 1989 reported that all HDMs were killed by dry clea- ning in perchloroethylene. Watanabe and colleagues 1995 found that dry cleaning of blankets with perchloroethylene reduced levels of Der p 1 by a mean of 69 and Der p 2 by an average of 54. These levels of allergen reduction are significantly less than would be achieved through washing at 55ºC.

3.3.4.5. Vacuuming

Householders primarily use vacuuming to remove dirt and dust from carpets and other floor coverings, but in this way they are also able to reduce the quantity of allergen within the home. However, this can take a substantial period of time de Boer, 1990b and is best achieved by regular vacuuming Munir, Einarsson Dreborg, 1993. The concentration of airborne allergens has been found to increase significantly after vacuuming with a stan- dard vacuum cleaner, thus increasing the risk of exposure to these allergens. This can be minimized when vacuum cleaners are fitted with high efficiency filters Kalra et al., 1990. Vacuuming an area has been shown to decrease the number of mites present Hill, 1998, although it does not remove all of them. Bischoff, Fischer Liebenberg 1992 reported that vacuuming a 1 m 2 area of carpet for two minutes may only remove 10 of the HDM population. Hay 1995 vacuumed the surface area of a spring mattress and recorded a population density of 3–46 living mites per m 2 , three orders of magnitude lower than the estimate of 8,200 m 2 26,800 living mites per m 2 obtained by extracting mites from a core taken from the upper 1.5 cm of the same mattress. This demonstrates not only the inef- House dust mites 106 Finally, the evidence on the effect of air conditioning is conflicting. Some studies have found a beneficial effect on mite numbers and allergen levels Lintner Brame, 1993; van Strien et al., 2004, while others have not Chan-Yeung et al., 1995; Chew et al., 1998. When considering the suitability of air-conditioning as a possible solution for controlling mites, its energy requirements should be taken into account. Smaller scale mechanical systems that modify environmental conditions, such as porta- ble dehumidifiers and bed heaters, are discussed in sections 3.3.5 and 3.3.8.

3.3.3.4. N on-mechanical passive ventilation systems