Endotoxin exposure in inner-city schools and homes of children with asthma.

Abstract

Endotoxins are stimulators of the immune system and, despite their potential to protect against allergy, have been associated with early wheezing and asthma morbidity.
To compare inner-city school endotoxin exposure with home endotoxin exposure in children with asthma.
Students with asthma were recruited from 12 urban elementary schools. Settled and airborne dust samples, linked to enrolled students, were collected from school classrooms, gymnasiums, and cafeterias twice during the academic year. For comparison, settled dust was collected once from the bedrooms of students with asthma.
Two hundred twenty-nine school settled dust samples and 118 bedroom settled dust samples were collected and analyzed for endotoxin. The median endotoxin concentration for school samples was 13.4 EU/mg (range, 0.7-360.7 EU/mg) and for home samples was 7.0 EU/mg (range = LLOD-843.0 EU/mg). The median concentration within each individual school varied from 6.6 EU/mg to 24.0 EU/mg. One hundred four students with asthma had matched classroom and bedroom endotoxin exposure measurements performed in the same season and demonstrated significantly higher concentrations of endotoxin in the students' classrooms (mean log value, 1.13 vs 0.99, P = .04). The median of the classrooms was 12.5 EU/mg compared with their bedrooms, with a median of 7.0 EU/mg. Within the school environment, no significant difference was seen between the fall and spring samples (mean log value 1.14 vs 1.09; P = .35).
Inner-city children with asthma were exposed to higher concentrations of endotoxin in their classrooms as compared with their bedrooms. Further studies are needed to evaluate school endotoxin exposure as a factor in asthma morbidity.

Full text

Page 1

Endotoxin Exposure in Inner-City Schools and Homes of
Children with Asthma
William J. Sheehan, MDa,b, Elaine B. Hoffman, PhDc, Chunxia Fu, MSd, Sachin Baxi, MDa,b,
Ann Bailey, BSd, Eva-Maria King, MSc, PhDe, Martin D. Chapman, PhDe, Jeffrey P. Lane,
CIH, MPHf, Jonathan M. Gaffin, MD, MMScb,g, Perdita Permaul, MDb,h, Diane R. Gold, MD,
MPHb,d, and Wanda Phipatanakul, MD, MSa,b,d
aDepartment of Pediatrics, Division of Allergy and Immunology, Children’s Hospital, Boston, MA
bHarvard Medical School, Boston, MA
cDepartment of Biostatistics, Harvard School of Public Health, Boston, MA
dDivision of Respiratory Epidemiology, Channing Laboratory, Brigham and Women’s Hospital,
Boston, MA
eIndoor Biotechnologies Inc, Charlottesville, VA
fFacilities Management
gDepartment of Pediatrics, Division of Pulmonology, Children’s Hospital, Boston, MA
hDivision of Pediatric Allergy and Immunology, Massachusetts General Hospital, Boston, MA
INTRODUCTION
Endotoxins or lipopolysaccharides (LPS) are part of the outer membrane of Gram negative
bacteria and are shed into the environment after bacteria die.1 Endotoxins are widely
distributed in our environment and are potent stimulators of the immune system. Early
exposure to endotoxin may result in a decreased TH2 profile2, 3 and may be protective
against the development of atopic conditions.2, 4–6 In contrast, possibly as an irritant or a
modifier of pulmonary responsiveness to allergens, increased endotoxin exposure has been
associated with both the development of early childhood wheezing and increased current
asthma symptoms in subjects already diagnosed with asthma.4, 7–15
High levels of endotoxins exist in work environments such as agricultural areas, animal
production facilities, waste processing, and textile production.16 In homes, higher levels of
endotoxin have been associated with indoor pets, carpeting, air conditioning, and farming
exposures.17–19 There are some studies that have demonstrated the presence of endotoxins in
daycare centers and schools,20–24 but these studies do not have home levels for comparison
of the relative school endotoxin exposure. Our study is designed to evaluate both the school
and home environments in a cohort of inner-city children with asthma. Given the important
Corresponding Author: Wanda Phipatanakul, MD, MS, Children’s Hospital, Boston, 300 Longwood Ave. Boston, MA 02115,
617-355-6117 Phone, 617-730-0310 Fax, wanda.phipatanakul@childrens.harvard.edu.
Authorship credit: (1) conception and design of the study; (2) data generation (when applicable); (3) analysis and interpretation of
the data; and (4) preparation or critical revision of the manuscript.
1, 2, 3, 4: Sheehan, Hoffman, Bailey, Gaffin, Gold, Phipatanakul
2, 3, 4: Fu, Baxi, King, Chapman, Permaul
1, 2, 4: Lane
None of the authors have any conflicts of interest related to this research project.
NIH Public Access
Author Manuscript
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
Published in final edited form as:
Ann Allergy Asthma Immunol. 2012 June ; 108(6): 418–422. doi:10.1016/j.anai.2012.04.003.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 2

association of endotoxin and asthma, our goal was to evaluate the school endotoxin
exposure relative to the home endotoxin exposure in children with asthma. Additionally, we
aimed to determine if animal allergen concentrations were associated with endotoxin
concentrations.
METHODS
This evaluation of endotoxin exposure in homes and schools is a sub-study of the School
Inner-City Asthma Study (SICAS). SICAS is an observational, prospective study evaluating
specific factors in both the home and school environments related to asthma morbidity. In
this study, 500 elementary school aged children with asthma are being recruited from 35–40
metropolitan schools over 5 years. Students are recruited annually and prospectively
followed during the subsequent academic year to monitor asthma morbidity. During the
academic year, enrolled students’ school and home environments are sampled for allergen
exposure in order to determine school and classroom-specific environmental risk factors,
relative to home exposures, associated with asthma morbidity. The primary hypothesis of
SICAS is that exposure to indoor allergens in the classroom will increase the risk of asthma
morbidity, even after controlling for home allergen exposures.
The focus of the study in this paper is a sub-study made possible through supplemental
funding (ACAAI Young Faculty Support Award) obtained to analyze a subset of
environmental dust samples for endotoxin. The endotoxin sub-study measured endotoxin
concentrations in schools and homes of children with asthma enrolled in SICAS during the
study’s first two years. All of the students during this time period were recruited from 12
inner-city elementary schools. Written informed consent was obtained and this study was
approved by the Children’s Hospital Boston institutional review board.
School Environment Assessment
In each school, settled dust samples were vacuumed from individual classrooms,
gymnasiums, and cafeterias as a measure of school-wide exposure. School settled dust
samples were collected twice during the academic year, once in the fall and once in the
spring, and were linked to the enrolled student. All students also provided a home bedroom
settled dust sample as a measure of home exposure. All school settled dust samples were
collected in the same manner. Briefly, an Oreck XL (model BB870-AD) vacuum was used
with a dust collector filter (DACI labs, Johns Hopkins, Baltimore, MD) fitted on the inlet
hose.25, 26 Vacuuming of the settled dust sample was performed for a total of 6 minutes per
sample, 3 minutes on the floor and 3 minutes on other surfaces, such as desks and chairs, as
previously described.27 Collected dust was sifted through a 40-mesh metal sieve (>425
micron particle exclusion), aliquoted, and stored at −20°C until extraction.
Home Environmental Assessment
In the home environment, dust samples were collected from the students’ bedrooms in a
similar manner as described in previous studies.28 In the students’ bedrooms, the area
around the bed was sampled. To do this, dust was vacuumed from both the child’s mattress
and from the bedroom floor. Settled dust samples were collected from the subjects’
bedrooms once during the year of observation.
Measurement of Endotoxin and Allergens in Dust Samples
Collected dust was extracted in pyrogene-free water/0.05% Tween 20 and serially diluted
for inclusion in the chromogenic Limulus Amoebocyte Lysate (LAL) assay (Lonza,
Walkersville, MD) for measurement of endotoxin. The concentration of endotoxin was
measured using the units of EU/mg. The lower limits of detection (LLOD) were 0.5 EU/mg
Sheehan et al.
Page 2
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 3

for endotoxin. The LLOD for measured allergens was 0.004 μg/g for Fel d 1, 0.012 μg/g for
Can f 1, and 0.002 μg/g for Mus m 1.
Seasonal Analysis
For purposes of analysis, the year was divided into “Fall” and “Spring” seasons. The “Fall”
season was defined as any time from September to March with the vast majority of samples
being collected in September, October, and November. The “Spring” season was defined as
any time between April to August with the vast majority of the samples collected in April,
May, and June. School samples were collected twice during the year, once in each of the
seasons with approximately 6 months between the collections of each sample. Home
samples were collected once during the year. These school and home samples were linked to
individual children with asthma. Home samples were matched to the school sample that was
performed within the same season and the time interval between sampling the home and
school was typically within two months.
Statistical Analysis
Medians were calculated for endotoxin levels in each setting (schools and homes) and for
each season (fall and spring) in the school samples. Values below the LLOD were assigned
the limit of detection for all statistical analyses. Each enrolled subject had personal links that
identified their bedroom, their school, and their exact classroom. Statistical analysis was
performed on settled dust samples of matched students’ classrooms and bedrooms collected
in the same season. Additionally, analyses were conducted on matched fall and spring
school samples. Endotoxin concentrations were log transformed so the distributions were
approximately normal for parametric statistical tests and correlations. Paired t-tests on log
transformed variables were used where p-values are reported. Pearson correlations were
computed for log transfored variables to determine levels of associations. Finally, allergen
concentrations for cat, dog, and mouse were evaluated as possible predictors of elevated log
transformed endotoxin concentrations using generalized linear models to account for the
clustering of students within schools (SAS 9.12, Cary, NC).
RESULTS
A total of 347 settled vacuumed dust samples were collected over the two year period. In the
subjects’ schools, a total of 229 settled dust samples were collected from multiple rooms in
12 different schools (5 schools in year 1 and 7 schools in year 2). School samples were
collected twice during the academic year with 117 settled dust samples collected in the fall
and 112 settled dust samples collected in the spring. Also, 118 bedroom settled dust samples
were collected.
In the school dust samples, 100% (229 of 229) had detectable levels of endotoxin with a
median concentration of 13.4 EU/mg. In the home dust samples, 96.6% (114 of 118) had
detectable endotoxin levels with a median concentration of 7.0 EU/mg. Additional
information on the overall home and school endotoxin concentrations including levels for
different schoolrooms, such as classrooms, cafeterias, and gymnasiums, are included in
Table 1.
A total of 104 enrolled subjects with asthma had matched samples collected from their
bedroom and their classroom in the same season. In this subset of matched samples, the
classroom endotoxin concentration was significantly higher than the bedroom endotoxin
concentration (mean log value = 1.13 vs. 0.99, mean difference = 0.144, 95% CI of
difference = 0.009–0.278, p = 0.04, paired t-test). The classroom median endotoxin
concentration of 12.5 EU/mg (range = 0.7 – 360.7 EU/mg) was higher than the median
Sheehan et al.
Page 3
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 4

bedroom endotoxin concentration of 7.0 EU/mg (range = <0.5 – 843.0 EU/mg). On an
individual-student basis, 59% of these subjects (61 of 104) had higher concentrations of
endotoxin in their classroom than in their bedroom.
There was wide variability between endotoxin concentrations in dust samples across the 12
schools as seen in Figure 1. The median dust endotoxin concentration at each of the
individual schools ranged from 6.6 EU/mg (School 10) to 24.0 EU/mg (School 5). For
comparison, Figure 1 also includes the median endotoxin concentration of the homes of
students attending that particular school. Additionally, a line on Figure 1 has been drawn to
demonstrate the median concentration for dust endotoxin in home bedroom samples (7.0
EU/mg). As depicted in Figure 1, all but one of the schools had a median dust endotoxin
concentration that rose above the median dust endotoxin level for home bedroom samples.
When comparing school settled dust endotoxin concentrations in the fall to those in the
spring, no difference was detected (mean log value = 1.14 vs. 1.09, mean difference = 0.048,
95% CI of difference = −0.054–0.150, p = 0.35, paired samples t-test). For this comparison,
111 rooms within the schools had matching fall and spring samples collected. The median
settled dust endotoxin concentrations in fall samples was 14.4 EU/mg (range 0.7 – 360.7
EU/mg) as compared to spring samples in the same rooms with a median settled dust
endotoxin concentration of 12.9 EU/mg (range 0.8 – 206.5 EU/mg). Although no difference
was detected, there was a weak correlation detected between the fall and spring schoolroom
samples (r=0.23).
Finally, dust samples were evaluated to see if higher allergen concentrations were associated
with higher endotoxin concentrations. As seen in Table 2, higher concentrations of dog and
cat allergens in school dust samples were associated with higher concentrations of endotoxin
when adjusting variances for within school variability and repeated observations. There
were significant differences in endotoxin concentrations between the schoolrooms in the
higher tertiles of cat and dog allergens as compared to the lowest tertile. In contrast, there
were no differences in settled dust endotoxin concentration between the schoolrooms when
grouped by tertile level of settled dust mouse allergen (data not shown).
DISCUSSION
In our study, inner-city children with asthma were exposed to higher concentrations of
endotoxin in their school classrooms as compared to their home bedrooms. To our
knowledge, this is the first study to directly compare school endotoxin exposure to home
endotoxin exposure in children with asthma. This result demonstrates that in an urban
environment, schools, and not homes, may represent the most significant location for
endotoxin exposure. Given that children spend a large proportion of their childhood in
school, this endotoxin exposure may substantially contribute to asthma morbidity. Further
studies are needed to evaluate the school environment as a cause of asthma morbidity.
Previous studies have found detectable endotoxin in schools, but did not evaluate students’
homes. As expected, Andersson et al discovered that endotoxin levels in daycares and
schools were lower than endotoxin levels found in animal sheds;20 however, the home
environment provides a better comparison for childhood exposure. Most previous studies
have evaluated places of education for the youngest children, such as daycare centers and
pre-elementary schools.21, 23, 24 Interestingly, Rullo et al demonstrated that these facilities
for younger children had endotoxin levels that were three times higher than endotoxin levels
in elementary schools for older children. Our study evaluated elementary schools and found
the endotoxin concentrations to be higher than homes. It is possible that if we evaluated
Sheehan et al.
Page 4
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 5

daycares or preschool settings, the differential over home endotoxin concentrations may
have been even greater.
Another factor important to our study was the inner-city environment. Our comparison
showed higher concentrations in urban schools as compared to urban homes, but it is
difficult to translate these findings to a rural environment. Morcos et al found that rural
schools have higher levels of endotoxin as compared to urban schools.22 Likewise, higher
levels of endotoxin have been found in rural homes, especially those homes in close
proximity to farm animals.19 Based on these studies, it would be expected that both rural
schools and rural homes would have higher exposure of endotoxin, but the comparison
between schools and homes in these communities is unknown.
Previous studies have demonstrated that predictors of increased endotoxin levels include
pets, carpeting, moisture sources, increased total dust, and increased inhabitants in a living
area.17, 18 For our study, the number of residents in the home was not correlated with the
bedroom endotoxin concentration (r = 0.02). In the schools, the age of the school was not
correlated with the concentration of endotoxin (r = −0.08). There was no correlation
between the matched school and home samples when evaluating endotoxin concentrations (r
= 0.16). None of our schools had pets, and the majority of our schoolrooms did not have
carpeting. It is possible that the increased number of children in each classroom, as
compared to a bedroom, could have contributed to our findings. This is supported by our
finding that levels of dog and cat allergens were associated with higher concentrations of
endotoxin in the schools. Given that there were no pets in the schools, this association may
indicate that children are tracking endotoxin into the schools along with pet allergens.
We acknowledge that we have measured endotoxin concentration in the collected dust
samples and not total endotoxin load. Previous studies have demonstrated that endotoxin
concentration (EU/mg) and endotoxin load (EU/m2) are highly correlated.14, 15 Additionally,
endotoxin concentration has been used in primary analyses in a number of previous
studies. 9, 11, 14 We present medians rather than means because our dataset has a wide range
of values and we do not want a couple of extreme observations to overly influence results
that use means. Irrespective of this, p-values were calculated on log transformed data that
was normally distributed.
We recognize that our median endotoxin concentrations are lower than those found in
previous studies in rural communities19, metropolitan areas3, and inner-city studies.14
Although our median levels are lower than previous studies, our ranges of concentration
were wide with some samples having very high concentrations of endotoxin similar to
previous reports. Our lower median concentration may be related to a variety of factors
including climate, neighborhoods, and relatively few pets in our cohort. Another factor is the
complete lack of detectable cockroach allergen in our settled dust samples. We did not have
any home or school samples with detectable cockroach allergen in our cohort. Previously,
Thorne et al demonstrated that cockroach allergen has been associated with elevated
endotoxin levels.29 However, our lower concentrations may also be related to inter-
laboratory variations. Due to large inter-laboratory variations between the protocols used for
analyses of endotoxins, it is generally recommended that only intra-laboratory results are
directly compared.16 As such, our discovered concentrations should not be compared with
other studies, but should be compared within our own study. Given this, our lower
concentrations do not detract from our primary conclusion that, in our study, there was a
higher concentration of endotoxin in the school classrooms as compared to the home
bedrooms. We can not, at this time, make a statement regarding the possible implications of
these discovered concentrations on asthma morbidity, but we recognize that schools should
be considered important when evaluating exposures that may be related to asthma morbidity.
Sheehan et al.
Page 5
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 6

One of our limitations is that our home sample was from the bedroom and not from other
rooms in the home. It is possible that other rooms in the home may have higher
concentrations of endotoxin due to a number of factors that may be present in non-bedroom
areas, such as pets, moisture sources, more foot traffic, and closer proximity to home
entrances. We chose the child’s bedroom as this was the site of sampling for previous
asthma studies, such as the National Cooperative Inner-City Asthma Study which
demonstrated bedroom allergen exposure to be associated with asthma morbidity.30
Additionally, interventional studies have shown that reduction of allergen levels in the
bedroom resulted in improved asthma control.31 Focusing on the bedroom makes sense as
this is the place were the child spends at least 7–8 hours each night. Within a 24 hour period,
this is likely the one room in a home where children spend the most time. This bedroom
exposure is comparable to their classroom exposure assuming that they spend approximately
7 hours per day in school. Thus, we designed our study for the main comparison between the
classroom and the bedroom.
Another limitation of our study is the potential bias that may arise from selecting a
population with asthma. We do not expect their school environments to differ from children
without asthma, but it is possible that their home environments may differ. For example,
children with asthma and animal allergies may be less likely to have a pet in their home or
allow a pet in their bedroom which would possibly decrease the amount of endotoxin in their
bedroom. In our study, 24.1% of the enrolled subjects reported having cats or dogs in their
home. Additionally, parents of children with asthma may be more likely to keep their child’s
bedroom cleaner which may result in less endotoxin compared to non-asthmatic children.
Regardless of the possible bias, the importance of the comparison in children with asthma is
that it may affect the child’s asthma morbidity. If families of children with asthma are
undertaking practices that decrease home endotoxin exposure, then the school endotoxin
exposure becomes even more important as parents have little, if any, control over this
environment.
Future studies should evaluate if school endotoxin exposure is associated with asthma
morbidity, controlling for home exposure. If school-based exposures are found to be
important in asthma morbidity, then interventional strategies should be aimed at the schools.
For years, physicians have been suggesting tactics to help improve the home environments
for children with asthma. Targeting school-based environmental exposures may prove to be
a cost-effective way to improve asthma health of many children.
Acknowledgments
Financial Support: Foundation of ACAAI, Young Faculty Support Award (Dr. Phipatanakul)
NIH Grants: R01 AI 073964 and R01 AI 073964-02S1.
Dr. Sheehan received partial support from T32-AI-007512
This work was conducted with support from Harvard Catalyst Catalyst | The Harvard Clinical and Translational
Science Center (NIH Award #UL1 RR 025758 and financial contributions from Harvard University and its
affiliated academic health care centers). The content is solely the responsibility of the authors and does not
necessarily represent the official views of Harvard Catalyst, Harvard University and its affiliated academic health
care centers, the National Center for Research Resources, or the National Institutes of Health
References
1. Zhu Z, Oh SY, Zheng T, Kim YK. Immunomodulating effects of endotoxin in mouse models of
allergic asthma. Clin Exp Allergy. Apr; 40(4):536–546. [PubMed: 20447074]
Sheehan et al.
Page 6
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 7

2. Braun-Fahrlander C, Riedler J, Herz U, et al. Environmental exposure to endotoxin and its relation
to asthma in school-age children. N Engl J Med. Sep 19; 2002 347(12):869–877. [PubMed:
12239255]
3. Abraham JH, Finn PW, Milton DK, Ryan LM, Perkins DL, Gold DR. Infant home endotoxin is
associated with reduced allergen-stimulated lymphocyte proliferation and IL-13 production in
childhood. J Allergy Clin Immunol. Aug; 2005 116(2):431–437. [PubMed: 16083802]
4. Celedon JC, Milton DK, Ramsey CD, et al. Exposure to dust mite allergen and endotoxin in early
life and asthma and atopy in childhood. J Allergy Clin Immunol. Jul; 2007 120(1):144–149.
[PubMed: 17507083]
5. Karadag B, Ege MJ, Scheynius A, et al. Environmental determinants of atopic eczema phenotypes
in relation to asthma and atopic sensitization. Allergy. Dec; 2007 62(12):1387–1393. [PubMed:
17983373]
6. Sordillo JE, Hoffman EB, Celedon JC, Litonjua AA, Milton DK, Gold DR. Multiple microbial
exposures in the home may protect against asthma or allergy in childhood. Clin Exp Allergy. Jun;
40(6):902–910. [PubMed: 20412140]
7. Horick N, Weller E, Milton DK, Gold DR, Li R, Spiegelman D. Home endotoxin exposure and
wheeze in infants: correction for bias due to exposure measurement error. Environ Health Perspect.
Jan; 2006 114(1):135–140. [PubMed: 16393671]
8. Leung TF, Wong YS, Chan IH, et al. Indoor determinants of endotoxin and dust mite exposures in
Hong Kong homes with asthmatic children. Int Arch Allergy Immunol. 152(3):279–287. [PubMed:
20150746]
9. Park JH, Gold DR, Spiegelman DL, Burge HA, Milton DK. House dust endotoxin and wheeze in
the first year of life. Am J Respir Crit Care Med. Feb; 2001 163(2):322–328. [PubMed: 11179100]
10. Rennie DC, Lawson JA, Kirychuk SP, et al. Assessment of endotoxin levels in the home and
current asthma and wheeze in school-age children. Indoor Air. Dec; 2008 18(6):447–453.
[PubMed: 18681911]
11. Rizzo MC, Naspitz CK, Fernandez-Caldas E, Lockey RF, Mimica I, Sole D. Endotoxin exposure
and symptoms in asthmatic children. Pediatr Allergy Immunol. Aug; 1997 8(3):121–126.
[PubMed: 9532251]
12. Zhao Z, Sebastian A, Larsson L, Wang Z, Zhang Z, Norback D. Asthmatic symptoms among
pupils in relation to microbial dust exposure in schools in Taiyuan, China. Pediatr Allergy
Immunol. Aug; 2008 19(5):455–465. [PubMed: 18221461]
13. Michel O, Kips J, Duchateau J, et al. Severity of asthma is related to endotoxin in house dust. Am J
Respir Crit Care Med. Dec; 1996 154(6 Pt 1):1641–1646. [PubMed: 8970348]
14. Perzanowski MS, Miller RL, Thorne PS, et al. Endotoxin in inner-city homes: associations with
wheeze and eczema in early childhood. J Allergy Clin Immunol. May; 2006 117(5):1082–1089.
[PubMed: 16675336]
15. Thorne PS, Kulhankova K, Yin M, Cohn R, Arbes SJ Jr, Zeldin DC. Endotoxin exposure is a risk
factor for asthma: the national survey of endotoxin in United States housing. Am J Respir Crit
Care Med. Dec 1; 2005 172(11):1371–1377. [PubMed: 16141442]
16. Radon K. The two sides of the “endotoxin coin”. Occup Environ Med. Jan; 2006 63(1):73–78. 10.
[PubMed: 16361410]
17. Giovannangelo M, Gehring U, Nordling E, et al. Determinants of house dust endotoxin in three
European countries - the AIRALLERG study. Indoor Air. Feb; 2007 17(1):70–79. [PubMed:
17257154]
18. Park JH, Spiegelman DL, Gold DR, Burge HA, Milton DK. Predictors of airborne endotoxin in the
home. Environ Health Perspect. Aug; 2001 109(8):859–864. [PubMed: 11564624]
19. Waser M, Schierl R, von Mutius E, et al. Determinants of endotoxin levels in living environments
of farmers’ children and their peers from rural areas. Clin Exp Allergy. Mar; 2004 34(3):389–397.
[PubMed: 15005732]
20. Andersson AM, Weiss N, Rainey F, Salkinoja-Salonen MS. Dust-borne bacteria in animal sheds,
schools and children’s day care centres. J Appl Microbiol. Apr; 1999 86(4):622–634. [PubMed:
10212408]
Sheehan et al.
Page 7
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 8

21. Instanes C, Hetland G, Berntsen S, Lovik M, Nafstad P. Allergens and endotoxin in settled dust
from day-care centers and schools in Oslo, Norway. Indoor Air. Oct; 2005 15(5):356–362.
[PubMed: 16108908]
22. Morcos MM, Morcos WM, Ibrahim MA, Shaheen MA. Environmental exposure to endotoxin in
rural and urban Egyptian school children and its relation to asthma and atopy. Minerva Pediatr.
Feb; 63(1):19–26. [PubMed: 21311426]
23. Oldfield K, Siebers R, Crane J. Endotoxin and indoor allergen levels in kindergartens and daycare
centres in Wellington, New Zealand. N Z Med J. 2007; 120(1248):U2400. [PubMed: 17277816]
24. Rullo VE, Rizzo MC, Arruda LK, Sole D, Naspitz CK. Daycare centers and schools as sources of
exposure to mites, cockroach, and endotoxin in the city of Sao Paulo, Brazil. J Allergy Clin
Immunol. Oct; 2002 110(4):582–588. [PubMed: 12373265]
25. Mitchell H, Senturia Y, Gergen P, et al. Design and methods of the National Cooperative Inner-
City Asthma Study. Pediatr Pulmonol. Oct; 1997 24(4):237–252. [PubMed: 9368258]
26. Phipatanakul W, Cronin B, Wood RA, et al. Effect of environmental intervention on mouse
allergen levels in homes of inner-city Boston children with asthma. Ann Allergy Asthma
Immunol. Apr; 2004 92(4):420–425. [PubMed: 15104193]
27. Smedje G, Norback D, Edling C. Asthma among secondary schoolchildren in relation to the school
environment. Clin Exp Allergy. Nov; 1997 27(11):1270–1278. [PubMed: 9420130]
28. Arbes SJ Jr, Sever M, Vaughn B, et al. Feasibility of using subject-collected dust samples in
epidemiologic and clinical studies of indoor allergens. Environ Health Perspect. Jun; 2005 113(6):
665–669. [PubMed: 15929886]
29. Thorne PS, Cohn RD, Mav D, Arbes SJ, Zeldin DC. Predictors of endotoxin levels in U.S.
housing. Environ Health Perspect. May; 2009 117(5):763–771. [PubMed: 19479019]
30. Rosenstreich DL, Eggleston P, Kattan M, et al. The role of cockroach allergy and exposure to
cockroach allergen in causing morbidity among inner-city children with asthma. N Engl J Med.
May 8; 1997 336(19):1356–1363. [PubMed: 9134876]
31. Kattan M, Stearns SC, Crain EF, et al. Cost-effectiveness of a home-based environmental
intervention for inner-city children with asthma. J Allergy Clin Immunol. Nov; 2005 116(5):1058–
1063. [PubMed: 16275376]
Sheehan et al. Page 8
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 9

FIGURE 1. Median Endotoxin Concentration in Each Inner-City School as Compared to Homes
of Students Attending that Particular School
Black Bars Represent the Median School Endotoxin Concentration
Grey bars represent the Median Home Endotoxin Concentration
Dashed Line Shows Median Home Concentration for All Samples
Sheehan et al.Page 9
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.
NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript

Page 10

NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript
Sheehan et al.Page 10
TABLE 1
Endotoxin Levels in Schools and Homes of Children with Asthma
Number of Samples Collected
Samples with Detectable Endotoxin
Median Endotoxin Level
Endotoxin Range
Endotoxin Interquartile Range
HOMES (All Bedrooms)
118
96.6% (114)
7.0 EU/mg
<0.5 – 843.0 EU/mg
4.6 – 22.5 EU/mg
SCHOOLS (All Rooms)
229
100% (229)
13.4 EU/mg
0.7 – 360.7 EU/mg
7.0 – 23.0 EU/mg
Different Schoolroom Types:
Classrooms
195
100% (195)
13.8 EU/mg
0.7 – 360.7 EU/mg
7.2 – 23.5 EU/mg
Cafeterias
22
100% (22)
16.0 EU/mg
0.9 – 126.8 EU/mg
9.0 – 27.8 EU/mg
Gymnasiums
12
100% (12)
5.6 EU/mg
2.3 – 21.3 EU/mg
3.2 – 8.3 EU/mg
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.

Page 11

NIH-PA Author Manuscript
NIH-PA Author Manuscript
NIH-PA Author Manuscript
Sheehan et al.Page 11
TABLE 2
School Dust Endotoxin Level by Tertile of Allergen Level
Number
Median Endotoxin Level
Mean Log Endotoxin Level (SD)
CAT ALLERGEN (Fel d 1)
Low
≤ 0.04 μg/g
76
9.6 EU/mg
0.98 (0.51)
Reference
Middle
> 0.04 – < 0.43 μg/g
76
10.7 EU/mg
1.12 (0.41)
p = 0.019
High
≥ 0.43 μg/g
77
16.7 EU/mg
1.23 (0.32)
p < 0.001
DOG ALLERGEN (Can f 1)
Low
≤ 0.012 μg/g
77
9.0 EU/mg
0.95 (0.51)
Reference
Middle
> 0.012 – < 0.15 μg/g
76
13.2 EU/mg
1.13 (0.42)
p = 0.003
High
≥ 0.15 μg/g
76
17.0 EU/mg
1.24 (0.32)
p < 0.001
Ann Allergy Asthma Immunol. Author manuscript; available in PMC 2012 June 05.