Longitudinal study of dust and airborne endotoxin in the home

Determinants of endotoxin levels in carpets in New Zealand homes

Endotoxin in house dust has been shown to be associated with asthma severity. Little is known about the influence of housing characteristics on endotoxin distribution. Using standardized methods, dust was sampled from a 1m(2) site and the whole accessible carpet area in selected Wellington, New Zealand homes (n = 77). Endotoxin was measured using a Limulus Amoebocyte Lysate assay. Relative humidity and temperature were recorded using sensors placed in carpet bases. Questionnaires were used to collect information on housing characteristics. All analyses were performed for endotoxin units (EU)/mg and EU/m2 for each site. Geometric mean endotoxin levels were 22.7 EU/mg [geometric standard deviation (GSD) = 2.4] or 30,544 EU/m2 (GSD = 3.2) from the 1m(2) site, and 28.4 EU/mg (GSD = 3.4) or 5653 EU/m2 (GSD = 6.4) from the whole room. After controlling for confounding, endotoxin was positively associated with dogs inside [geometric mean ratio (GMR): 0.9-2.0], total household occupants (GMR: 1.7-2.0, for 1 m2 sample only), vacuum cleaners <1-year old (GMR: 2.3-2.7), reusing vacuum dust collection bags (GMR: 1.4-3.1), steamcleaning or shampooing the carpet (GMR: 1.4-2.2) and high relative humidity (GMR: 1.4-1.6). Lower endotoxin was associated with floor insulation (GMR: 0.4-0.8), and north-facing living rooms (GMR: 0.4-0.8). This study has identified home characteristics that could be modified to reduce endotoxin exposure.

Reproducibility of allergen, endotoxin and fungi measurements in the indoor environment

Measurements of biocontaminants in settled house dust once a year are commonly used to assess long-term exposure. To examine stability over time and seasonal variation, we measured concentrations of mite and cat allergens, endotoxin and mold spores in living room floor dust in 745 German homes collected twice a year in two different seasons. The study population consisted of adults and children living in five different areas in Germany. All dust samples were collected in a standardized manner from the living room floor and taken during the years 1995 to 1998. The median interval between the two dust samplings was approximately 7 months. Mite and cat allergens were measured in settled house dust by monoclonal antibodies, endotoxin by the limulus amebocyte lysate method, and total spore counts by cultural methods. Crude Pearson's correlation coefficients between log-transformed concentrations in the first and second dust samples ranged between 0.65 and 0.75 for allergens, 0.59 for endotoxin and only 0.06 for total spore counts. The strongest and most consistent seasonal effects were observed for fungi with highest levels in July-September. Cat allergen concentrations were found consistently to be increased in January-March. Mite allergens did not show a strong and consistent seasonal pattern. We conclude that repeated measurements of mite and cat allergens and endotoxin in settled house dust improve the estimate for annual mean concentrations. However, even a single observation of these biocontaminants may be a good proxy for a 1-year exposure since repeated measures were highly correlated. However, repeated measurements of fungi levels were only weakly correlated and thus repeated observations for assessment of annual means of total spore counts are needed.

House dust endotoxin and allergic sensitization in children

A higher exposure to endotoxin was hypothesized to contribute to lower prevalence of allergic sensitization and hay fever in children growing up on a farm. We studied the association between house dust endotoxin and allergic sensitization. We randomly selected 740 children, aged between 5 and 10 years, from a group of children who participated in two cross-sectional surveys performed in Saxony-Anhalt, Germany, from 1992 to 1993 and from 1995 to 1996, such that 50% of the children were atopic or had a diagnosis of asthma. From 1996 to 1998, we collected living-room floor dust in the homes of 454 of these children (61%). The content of endotoxin in house dust was quantified using a chromogenic kinetic limulus amoebocyte lysate test and was related with health outcomes measured in the preceding cross-sectional surveys. Multiple logistic regression analyses adjusted for place of residence, sex, age, parental education, parental atopy, and pet ownership showed a negative association between exposure to endotoxin and sensitization to one or more allergens (aOR [95% CI] 0.95 [0.83; 1.10]) and two or more allergens (aOR [95% CI] 0.80 [0.67; 0.97]) using 0.35 kU/L as the cutoff value for sensitization. The protective effect was strengthened with increasing degree of sensitization. In conclusion, exposure to higher levels of house dust endotoxin is associated with lower prevalence of allergic sensitization in children.

Different effects of endotoxin versus mite and cat allergen exposure on T-cell differentiation in infants

BACKGROUND

Early exposure to bacterial endotoxin has been proposed to protect against allergy development in children. Whether endotoxin is able to direct T-cell differentiation into a predominance of type 1 immunity is still unresolved.

OBJECTIVE

We sought to compare the effects of endotoxin and mite and cat allergens on T-cell differentiation in infants.

METHODS

In a random population sample of 135 2-year-old children of an ongoing birth-cohort study, peripheral blood CD4+ and CD8+ T-cell subsets were defined by the expression of the chemokine receptors CCR5 and CCR3 as surrogate markers for type 1 and type 2 T cells, respectively. Endotoxin and mite and cat allergens were measured in house dust collected from the mother's mattress at the child's age of 3 months to assess early exposure.

RESULTS

In the CD4+ T-cell subset, endotoxin levels were positively associated with high proportions of type 1 CCR5+ cells (odds ratio for fourth exposure quartile [OR(Q4)], 7.68; 95% CI, 1.35-43.75), whereas cat allergen levels were associated with increased proportions of type 2 CCR3+ cells (OR(Q4), 4.07; 95% CI, 1.05-15.85). In contrast to endotoxin, allergen levels were associated with CD8+ T cells, showing an inverse relationship between mite allergen concentrations and high proportions of CCR5+ or CCR3+ cells (CCR5+ cells: OR(Q4), 0.14; 95% CI, 0.03-0.74; CCR3+ cells: OR(Q4), 0.16; 95% CI, 0.03-0.89) and a positive association of cat allergen levels with increased proportions of CCR5+ cells (OR(Q4), 9.24, 95% CI, 1.61-53.10), as well as CCR3+ cells (OR(Q3), 6.64; 95% CI, 1.21-36.51).

CONCLUSION

Our results indicate that endotoxin has the potential to promote the development of type 1 CD4+ T cells, whereas mite and cat allergens primarily modify the proportion of CD8+ cells of both types.

Dust mite allergens: mitigation and control

In recent years, greater attention has been given to the role of indoor allergens as a cause of sensitization and allergic respiratory diseases. Although indoor allergen control measures to reduce symptoms in individuals allergic to mites have produced controversial results, environmental allergen avoidance is today one of the four primary goals of asthma management recommended in several guidelines of asthma treatment. Exposure to high indoor aeroallergen levels, especially to house dust mite allergens, is an important environmental risk factor for allergic sensitization and the subsequent development and exacerbation of asthma. Therefore, effective aeroallergen avoidance is of use to prevent and treat allergic diseases. Although endotoxin exposure may be protective in early life, it has been demonstrated that the inhalation of endotoxin may exacerbate asthma in house dust mite sensitized patients. Mite-allergic asthmatic patients should be aware of the dangerous combination of mite allergen exposure associated with high endotoxin levels in house dust. These two immunologically active substances have been associated with severe asthma and seasonal exacerbation of symptoms. Effective house dust mite allergen avoidance will never be achieved using a single control measure; various methods are required to affect the multiple factors that facilitate high indoor allergen levels. Education of the patients and their families is also an important component of environmental control strategies.

Work-related asthma and implications for the general public

Asthma has been increasing over the last two decades in the United States. The onset of asthma has also been increasingly reported as a result of occupational exposures to over 350 different agents. Work-related asthma (WRA) has become the most frequently diagnosed occupational respiratory illness. Epidemiologic studies from the United States reported WRA incidence rates of 29-710 cases per million workers per year and suggest that 10-25% of adult asthma is work related. Much can be learned about asthma in the general population from investigations of asthma in the workplace. Surveillance of WRA continues to highlight an important role for low molecular weight chemical sensitizers, as well as high molecular weight antigens. Additionally, recent reports implicate mixed exposures, including commercial cleaning solutions, solvents, and other respiratory irritants, as well as contamination in nonindustrial environments, including schools and offices. Investigations of WRA have demonstrated a clear dose-related increase in sensitization and symptoms for exposures to both chemical and protein sensitizers. High proportions of exposed working groups can be affected. Skin exposures may affect the likelihood of individuals developing respiratory symptoms. Atopy increases the risk of sensitization and illness from workplace exposure to antigens but not to chemical sensitizers. Irritant exposures can act as adjuvants among individuals exposed to sensitizing substances, increasing the proportion who become sensitized. Atopy might also be a result of irritant exposures in some persons. Occupational asthma often has important long-term adverse health and economic consequences but can resolve completely with timely control of exposures. Detailed study of such asthma "cures" may prove useful in understanding factors that influence asthmatic airway inflammation in the general population.

Pollutants and asthma: role of air toxics

Asthma is a disease characterized by intermittent bronchoconstriction due to increased airway reactivity to both allergic and nonallergic stimuli. Most asthma exacerbations that result in hospitalization are associated with viral upper respiratory tract infections. Such infections typically induce T-helper type 1 (T(H)1) responses in the airway, involving activation of nuclear factor-kappaB (NF-Kappa B). However, a more recently appreciated cause of asthma exacerbation is exposure to pollutants, including ozone and various components of particulate matter (PM), including transition metals, diesel exhaust, and biologicals such as endotoxin. Although the role of air toxics in asthma pathogenesis remains incompletely examined, many components of PM that are active exacerbants of asthma are also prominent air toxics (metal ions and organic residues). These agents have been observed to activate NF-Kappa B. Reviewed in this article are the actions of specific air pollutants on airway inflammation in humans and potential common response pathways for ozone, PM, and several air toxics.

Endotoxin, atopy and asthma

Endotoxin is infamous for its ability to exacerbate existing allergy and asthma symptoms. Current research supports this phenomenon, demonstrating its significance in the home, as well as in the workplace. At the same time, evidence is emerging that exposure to endotoxin may drive immune development away from the T-helper lymphocyte type 2-mediated allergy and asthma profile. This fits in nicely with the 'hygiene hypothesis', which attributes the past century's rise in allergy and asthma to a reduction in microbial burden. Indeed, infections have been associated with less atopy and asthma. Recent investigations have suggested that naturally-occurring non-infectious exposure to microbial components such as endotoxin might mitigate atopy and asthma as well.

Endotoxin exposure in allergy and asthma: reconciling a paradox

Well-established evidence links endotoxin exposure, especially in the workplace, to airways disease. Endotoxin can increase disease severity by acting as a natural adjuvant to augment asthma and atopic inflammation. Recent studies suggest that it can even act on its own, causing a distinct endotoxic form of asthma. Other studies, however, contradict the paradigm that endotoxin's influence is solely a negative one. Epidemiologic associations of environmental endotoxin exposure with allergy and asthma prevention are consistent with hygiene hypothesis associations of other microbial exposures or infections with a lower incidence of atopic disease. Currently, microbe-derived products are being developed as potential therapies for allergy and asthma. Thus it is an ideal time to consider endotoxin as a prototype of a natural intervention with microbial components. Nature's ongoing experiment with endotoxin can provide clues for the development of effective and safe microbe-based products for disease treatment and prevention. This article will discuss (1) conventional paradigms in which endotoxin-induced immune modulation by T(H)1-type induction leads to mitigation of T(H)2-type immune development, allergen sensitization, and atopic inflammation; (2) newer concepts of T(H)1-type immune responses that may provide additional asthma-protective effects by preventing airways remodeling; (3) home and environmental features that significantly contribute to endotoxin exposure; (4) different aspects of asthma mediated by endotoxin exposure; and (5) how to understand endotoxin's paradoxical nature of serving as both friend and foe.

Does environmental endotoxin exposure prevent asthma?

The evidence as to whether exposure to environmental airborne endotoxin plays a protective or an inducing role in the development of asthma is reviewed. Studies of endotoxin and atopy, endotoxin and asthma, and farming and asthma are considered and, in each instance, a distinction is made between evidence of primary causation and evidence of secondary causation. It is concluded that, although it is plausible that bacterial endotoxin may protect against the development of asthma, there is considerable reason for caution regarding this hypothesis.

Predictors of airborne endotoxin in the home

We identified home characteristics associated with the level of airborne endotoxin in 111 Boston-area homes enrolled in a cohort study of home exposures and childhood asthma, and we developed a predictive model to estimate airborne endotoxin. We measured endotoxin in family-room air and in dust from the baby's bed, family room, bedroom, and kitchen floor. Level of airborne endotoxin was weakly correlated (r < 0.3) with level of endotoxin in each of the four types of dust samples and was significantly correlated with endotoxin in family-room dust (p < 0.05). Endotoxin in family-room dust accounted for < 6% of the variability of airborne endotoxin. In a multivariate model, certain home characteristics were positively (p < 0.05) associated with airborne endotoxin. These included current presence of dog (difference in level, dog vs. no dog = 72%, partial R(2 )= 12.8%), past presence of dog (partial R(2) = 5.5%), and endotoxin level in family-room dust (partial R(2) = 5.3%). Use of a dehumidifier (partial R(2) = 6.4%) was negatively associated (p = 0.02; difference = -31%) with airborne endotoxin. Other home characteristics were identified as important determinants of increased airborne endotoxin in this model, but individual coefficients were not statistically significant (alpha = 0.05): total amount of fine dust collected in the home (partial R(2 )= 3.8%), concrete floor in family room (3.7%), water damage (3.6%), and use of cool-mist humidifier in past year (2.7%). This multivariate model explained 42% of the variability of airborne endotoxin levels, a substantial improvement over that with dust endotoxin alone. Airborne endotoxin in Boston-area homes appears to be determined by the presence of dogs, moisture sources, and increased amounts of settled dust.

Metropolitan home living conditions associated with indoor endotoxin levels

BACKGROUND

Household endotoxin exposure in allergy and asthma has been gaining attention for its dual potential to exacerbate these conditions in individuals with established disease and to abrogate atopy before disease onset.

OBJECTIVE

We sought to better understand the home environmental and lifestyle factors influencing house dust endotoxin levels.

METHODS

From the homes of 86 infants with wheeze in metropolitan Denver, Colorado, house dust endotoxin (detected with a standardized Limulus Amebocyte Lysate assay) and common indoor allergen (Fel d 1, Can f 1, Der p 1, Der f 1, and Bla g 1) contents were quantified. Comprehensive home environment and lifestyle questionnaires were completed during home visits by trained study staff and parents.

RESULTS

House dust endotoxin levels were associated with only 2 home environmental features: animals in the home and the presence of central air conditioning. The strongest positive associations were found with animals in the home. Interestingly, the homes without cats or other animals revealed a negative correlation between house dust Fel d 1 and endotoxin (P =.03). Central air conditioning, especially during months of typical use, was associated with lower house dust endotoxin levels. No significant associations between house dust endotoxin levels and home dampness, number of household inhabitants or young children, cleaning frequency, or presence of tobacco smokers in the home were found.

CONCLUSIONS

Indoor endotoxin exposure can be increased by the presence of animals in the home and decreased with central air conditioning. In some homes without animals, where allergen exposure adequate for sensitization still occurs, there are lower levels of house dust endotoxin. Therefore in homes without animals, factors that influence allergen and endotoxin levels in house dust probably differ. Households with detectable allergen levels but low endotoxin levels may provide a predisposing environment for animal allergen sensitization.