Differential effects of air conditioning type on residential endotoxin levels in a semi-arid climate

Abstract

Residential endotoxin exposure is associated with protective and pathogenic health outcomes. Evaporative coolers, an energy-efficient type of air conditioner used in dry climates, are a potential source of indoor endotoxins; however, this association is largely unstudied. We collected settled dust biannually from four locations in homes with evaporative coolers (n=18) and central air conditioners (n=22) in Utah County, Utah (USA), during winter (Jan-Apr) and summer (Aug-Sept), 2014. Dust samples (n=281) were analyzed by the Limulus amebocyte lysate test. Housing factors were measured by survey, and indoor temperature and relative humidity measures were collected during both seasons. Endotoxin concentrations (EU/mg) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons. Endotoxin surface loads (EU/m ) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons and in upholstered furniture during winter. For the nine significant season-by-location comparisons, EU/mg and EU/m were approximately three to six times greater in homes using evaporative coolers. A plausible explanation for these findings is that evaporative coolers serve as a reservoir and distribution system for Gram-negative bacteria or their cell wall components in homes.

Associations between evaporative cooling and dust‐mite allergens, endotoxins, and β‐(1 → 3)‐d‐glucans in house dust: A study of low‐income homes

“…16 Johnston et al, in a study of middle-income homes in Utah, reported endotoxin levels three to six times higher in homes with evaporative coolers compared to homes with central air conditioners. 18 Similarly, Lemons et al found that endotoxin levels were approximately three times greater in homes with evaporative coolers compared to homes with central air conditioners in the Reno, NV area. 19 Although endotoxin levels were relatively low in our study, the observed proportional differences in endotoxin levels between the two types of air conditioning systems are consistent with Lemons et al and Johnston et al, suggesting that evaporative coolers do tend to significantly increase residential endotoxin levels.…”

“…3 Children spend approximately 60%-80% of their time, 4 and adults spend approximately 70% of their time indoors at home, 5,6 making the home a key microenvironment for bioaerosol exposure. [17][18][19][20] Evaporative coolers are predominantly used in climates with low relative humidity (RH) and seasonally high outdoor temperatures 21 such as the Rocky Mountain States in the US. A few studies also suggest that evaporative coolers may significantly alter the bioaerosol profile in homes for immunologically important exposures such as house dustmite (HDM) allergens Der p1 and Der f1, bacterial endotoxins, and β-(1 → 3)-d-glucans.…”

“…[17][18][19][20] Evaporative coolers are predominantly used in climates with low relative humidity (RH) and seasonally high outdoor temperatures 21 such as the Rocky Mountain States in the US. 18,19 Early-life exposure to endotoxins, the lipopolysaccharide portion of the cell wall in Gram-negative bacteria, may confer protection against the development of allergic diseases, including asthma, [25][26][27][28][29] while simultaneously causing airway inflammation and asthma symptoms in children and adults. 20,22 The higher RH from evaporative coolers may create an ecological niche for HDMs to survive in arid and semi-arid climates, 17,20 potentially exposing home occupants to mite allergens.…”

“…A few studies also suggest that evaporative coolers may significantly alter the bioaerosol profile in homes for immunologically important exposures such as house dustmite (HDM) allergens Der p1 and Der f1, bacterial endotoxins, and β-(1 → 3)-d-glucans. [17][18][19][20] Evaporative coolers are predominantly used in climates with low relative humidity (RH) and seasonally high outdoor temperatures 21 such as the Rocky Mountain States in the US. Residential evaporative coolers remove heat from dry ambient air by drawing the air across a wetted filter media, resulting in lower indoor air temperature, but higher RH.…”

“…23 Furthermore, untreated evaporative cooler sump water provides a growth medium for Gram-negative bacteria during summer months 24 and may be a significant source of residential endotoxin load in homes. 18,19 Early-life exposure to endotoxins, the lipopolysaccharide portion of the cell wall in Gram-negative bacteria, may confer protection against the development of allergic diseases, including asthma, [25][26][27][28][29] while simultaneously causing airway inflammation and asthma symptoms in children and adults. [30][31][32][33] Finally, fungi are more common, and fungal species associated with allergies are more prevalent, in homes with evaporative coolers compared to homes with other forms of air conditioning.…”