Robert Graul and Faculty Mentor: Dr. James Johnston, Public Health – Health Science

Introduction
Asthma is the leading chronic disease among children in U.S. Low-income populations, minorities,
and children living in poor housing experience more emergency department visits, hospitalizations,
and deaths due to asthma that the general population. HDM allergens are linked to the exacerbation
of asthma and are found within homes all throughout the United States. Previous studies have shown
that HDM exposure is lower in arid and semi-arid climates, such as Utah, but robust data is still
lacking. Although HDM thrive in climates more humid than Utah, we have found that they are still
present based on certain indoor environmental factors.
Studies have shown that homes in dry climates with evaporative “swamp” coolers have a higher
prevalence of house dust mites (HDM) than homes with central air or no air conditioning. It also
appears that there is a relationship between evaporative cooler use and the presence of HDM based
on socio-economic factors. A previous study showed that low-income homes ( 200% of federal
poverty guidelines) in Utah County had detectable HDM allergens, but this study did not include a
comparison group. The purpose of our study was to evaluate levels of HDMs and their allergens in
low-income homes ( 100% of federal poverty level) in Utah County with evaporative coolers
compared with homes with central air or no air conditioning.
Methodology
Study homes (N=48) were recruited among individuals exiting the Woman, Infants, and Children
(WIC) office at the Utah County Health Department. All homes were in Utah County and used
evaporative cooling (N=20) or central air conditioning (N=28) during summer months. Interested
participants were excluded if they (1) used humidifiers or vaporizers, (2) previous water damage
covering more than 9.29 m2 (100 ft2), and (3) household income ≥100% of the 2017 Federal Poverty
Guidelines. During the sampling visit, study personnel administered a survey to collect information
about features of the home. Survey items included age of home, square footage, number of
residents, and age of mattress, furniture, and carpet (if applicable). Occupant density, reported as
number of people per 100 m2, was calculated from the number of residents and square footage of
each home.
Indoor air temperature and RH measurements were collected continuously for approximately 72 hrs
in each home between the months of July and October, 2017. Temperature and Humidity
measurements were collected using humidity/temperature dataloggers. These dataloggers were
placed in a central living area in the home and set to record temperature and RH every 5 minutes.
Outdoor air temperature and relative humidity measurements were collected from a weather
monitoring station located on the campus of Brigham Young University.
Reservoir dust samples were collected from four areas in each home: the homeowner’ s mattress, the
floor adjacent to the mattress, upholstered furniture in a main living area of the home, and the floor
adjacent to the upholstered furniture. Samples were collected from each surface by vacuuming within
a taped 1m2 area for 3 min. The samples were transferred to 15 ml polypropylene conical tubes, and
stored at 1.6° C until analyzed.
For mite analysis, 50 mg of dust from each sample were suspended in 25 ml of saturated sodium
chloride and a few drops of detergent with a Maxi-Mix. The suspension was rinsed through a 235
mesh (45 mm opening) sieve and the mites and dust retained on the sieve were stained with crystal
violet. The stain caused everything other than the mites to turn the color violet, making it easier to find
the almost transparent mites. After excess stain was rinsed off with distilled water, remaining material
was rinsed into an intergrid Petri dish and the live and dead mites were counted with the aid of a
stereoscope. All mites found were removed from each dust sample and cleared in lactic acid, which
makes species identification under microscope easier. Mites were then mounted on microscope
slides for species identification and gender analysis.
Results
Of the study homes, 28 with central air conditioning and 20 with evaporative coolers completed the
sampling. The average size of evaporative cooler homes was 91 m2 (979 ft2) whereas the average
size of central air conditioning homes was 104.7 m2 (1126.9 ft2). The homes in our study were an
average of 23.1m2 (249 ft2) smaller and had an occupation density 30.5% higher than the middleincome
homes sampled in a previous study in Utah. Homes with evaporative coolers had an average
RH and temperature of 44.5% and 23.3℃ respectively and homes with central air conditioning had an
average RH and temperature of 43.9% and 24.5℃. During the sampling period, the mean RH and
daily outdoor temperature were 38.5% and 19℃ respectively. Evaporative cooler homes did have an
occupation density (people/100m2) 17% higher than homes with central air conditioning. Both D.
pteronyssinus and D. farinae mites were found within homes with evaporative coolers and central air
conditioning. Prevalence of dust mites in evaporative cooler homes was 20% compared to 7% in
homes with central air conditioning
Discussion
The results found suggest that prevalence of house dust mites D. pteronyssinus and D. farinae as
well as their allergens (Der p 1 and Der f 1) may be higher in low-income homes with evaporative
coolers compared to homes with central air conditioning. The lower-income homes were on average,
significantly smaller and had higher occupation densities than homes previously studied. These may
be contributing factors, along with evaporative cooler use, for increased HDM levels. A regression
analysis needs to be created to determine the effects of collecting 40% of the evaporative cooler data
from homes during the month of October, when average temperature was lower than the previous
months. HDM allergen analysis is still being performed and results will provide improved data.
Conclusion
The results of our study suggest that low-income homes with evaporative coolers are more likely to
have higher prevalence of HDM and HDM allergens, specifically Der f 1. Our findings may be used in
future intervention studies to reduce HDM prevalence in low-income homes in semi-arid climates by
focusing on socioeconomic factors contributing to increased rates of allergy exposure. We hope that
this study will help to reduce the amount of emergency room visits, hospitalizations, and deaths due
to asthma.