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Reducing relative humidity to control the house dust mite Dermatophagoides farinae.

AUTHORS: Arlian LG; Neal JS; Vyszenski-Moher DL
AUTHOR AFFILIATION: Department of Biological Sciences, Wright State University, Dayton, Ohio 45435-0001, USA.
SOURCE: J Allergy Clin Immunol 1999 Oct; 104(4 Pt 1): 852-6
CITATION IDS: PMID: 10518832 UI: 99449684

BACKGROUND: Indoor relative humidity (RH) is the key factor that determines the survival and population development of the house dust mite Dermatophagoides farinae. Maintaining RH below 50% is one recommendation in a comprehensive plan to reduce house dust mites and mite allergen levels in homes. Even when mean daily RH is reduced below 50%, RH may rise above 50% intermittently for brief periods because of activities in the home (eg, cooking, bathing, and ventilation).
OBJECTIVE: The purpose of this study was to determine how brief daily periods of moist air alternating with long spells of low ambient RH (0% or 35%) influence population survival and growth of D farinae.
METHODS: Population growth was determined for D farinae at daily RH regimens of 2, 4, 6, and 8 hours at 75% or 85% RH alternating with 22, 20, 18, and 16 hours at 0% or 35% RH.
RESULTS: D farinae populations declined at daily regimens of 2 hours at 75% or 85% RH alternating with 22 hours at 0% or 35% RH. Daily regimens of 4, 6, and 8 hours at 75% RH alternating with 20, 18, and 16 hours, respectively, at 35% RH provided sufficient moisture for small growths in population size. These growths after 10 weeks were reduced by 98.2%, 98.0%, and 97.3% for daily regimens of 4, 6, and 8 hours, respectively, at 75% RH (with the remainder of the day at 35% RH) compared with the growth of populations continuously exposed to 75% RH. Continuous exposure to 85% RH inhibited population growth, but alternating daily regimens of 16, 18, and 20 hours at 35% RH allowed small populations to develop, although they were reduced by 99.4%, 98.8%, and 99.1% compared with population growth at a continuous 75%RH.
CONCLUSIONS: This study indicates that maintaining mean daily RH below 50%, even when RH rises above 50% for 2 to 8 hours daily, effectively restricts population growth of these mites and thus the production of allergen. To completely prevent population growth of D farinae, RH must be maintained below 35% for at least 22 hours per day when the daily RH is 75% or 85% for the remainder of the day.



AUTHORS: Lintner TJ; Brame KA
AUTHOR AFFILIATION: Vespa Laboratories, Inc., Spring Mills, PA 16785.
SOURCE: J Allergy Clin Immunol 1993 Apr; 91(4): 862-7
CITATION IDS: PMID: 8473674 UI: 93232476

BACKGROUND: Clinical evidence reveals a strong relationship between dust mite allergen levels and asthma. This study suggests the relative importance and interactions among factors that influence mite allergen levels in human dwellings.
METHODS: Dermatophagoides pteronyssinus allergen (Der p 1) and D. farinae allergen (Der f 1) were measured in 536 dust samples collected from 424 homes across the United States.
RESULTS: There were distinct seasonal fluctuations of Der p 1 and Der f 1. Der p 1 rapidly increased to peak in July then gradually decreased through October. Der f 1 slowly rose to peak later, around September, before declining. Different climates in regions of the United States had no significant effect on the quantity of Der p 1 or Der f 1. However, regional climate differences seemed to influence the prevalence of either D. pteronyssinus or D. farinae. Air-conditioning significantly reduced (p<0.0001) Der 1 mite allergens detected in the dust samples, and a tendency existed for Der f 1 to be higher than Der p 1 in air-conditioned homes. There was a significant (p<0.01) interaction between air-conditioning and seasons. The most dramatic effect was observed during the summer months, the cooling season, from approximately May to September.
CONCLUSIONS: These findings show that distinct seasonal fluctuations exist of D. pteronyssinus and D. farinae mite populations, and suggest that differences in the microclimate within homes may have a dramatic effect on Dermatophagoides mite populations.