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Lead Poisoning and Asthma
An Examination of Comorbidity
Scott N. Myers, MD;
Bruce Rowell, MD;
Helen J. Binns, MD, MPH
Arch Pediatr Adolesc Med. 2002;156:863-866.
ABSTRACT
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Objectives To determine the comorbidity of lead poisoning and asthma in urban children,
and to examine associated clinical factors.
Methods One-hundred-one patients at an inner-city clinic with blood lead levels
(BLLs) of 25 µg/dL or higher ( 1.2 µmol/L) (BLL25 group) were
randomly selected from a tracking lead database and matched on age, sex, and
primary language to 101 randomly selected patients with a first BLL recorded
in the database of lower than 5 µg/dL (<0.2 µmol/L) (BLL5 group)
and no subsequent BLLs of 10 µg/dL or higher (0.5 µmol/L).
Medical records were reviewed to determine diagnosis or symptoms of asthma
or wheezing at any visit, immunization status, and number of visits. Analyses
for matched pairs were conducted.
Results The BLL25 and BLL5 groups did not differ on age at diagnostic BLL (26.6
months vs 24.2 months), sex (54% male), or language (12% Spanish). The BLL25
and BLL5 groups had a similar number of subjects with a diagnosis of asthma
(6% vs 11%; odds ratio, 0.5; 95% confidence interval, 0.2-1.6); 26% of BLL25
and 34% of BLL5 subjects had either a diagnosis or symptoms of asthma or wheezing
(odds ratio, 0.7; 95% confidence interval, 0.4-1.3). Subjects with BLL25 were
more likely to have delayed immunization and a first clinic visit when older
than subjects with BLL5.
Conclusions There was no increased likelihood of asthma diagnosis or symptoms among
young children with lead poisoning. Children with lead poisoning also had
delayed medical care. These data may help guide interventions aimed at preventing
or reducing the impact of lead poisoning and asthma.
INTRODUCTION
LEAD POISONING and asthma are common pediatric health problems. Both
diseases have environmental mechanisms. Lead paint hazards are a primary source
for lead poisoning,1 and there is evidence
that exposure to household allergens increases asthma morbidity.2-4
Household dust is an important vector for both lead and allergens.4-6 Risk factors for both
diseases are similar. Urban, low-income, and minority children are at highest
risk for lead poisoning7-9
and asthma.10-15
Age and condition of housing are risk factors for lead poisoning16
and asthma.17-18
Home repair has been used for prevention and intervention efforts for
both diseases. Lead poisoning prevention efforts target repair of lead-based
paint hazards.19 Efforts to reduce household
allergen exposure target focused home remediation, particularly related to
dust, mold, and moisture control.20 There has
been a recent increase in funding to create environmentally "safe" homes,
an approach that encompasses control of both lead and allergen or asthma hazards.21-22 From 1993 through 2000, the US Department
of Housing and Urban Development Office of Lead Hazard Control (which recently
changed its name to the Office of Healthy Homes and Lead Hazard Control) awarded
a total of $552 million in lead hazard control grants under the Lead-Based
Paint Hazard Control Grant Program.23-24
In 1999 and 2000, the office also allocated grants of $10 million per fiscal
year for projects that address a broader concept of home safety, titled the
Healthy Homes Initiatives.21-22
Determining the degree of comorbidity between lead poisoning and asthma may
provide information to guide interventions aimed at preventing or reducing
the severity or impact of lead poisoning and asthma.
Chicago, Ill, has high rates of both lead poisoning and asthma, making
it an ideal location to examine the relationship between these 2 diseases.
In 1999, 18% of Chicago children tested had a blood lead level (BLL) of 10
µg/dL or higher (0.5 µmol/L).25
A recent study of Chicago kindergarten students reported that 10.8% of children
had diagnosed asthma, and there was a 30.1% prevalence of asthma symptoms
unassociated with the diagnosis of asthma.26
Asthma hospitalizations and mortality in Chicago are high and rising.27
We hypothesized that, because of the high likelihood of exposure to
environmental risk factors, children with lead poisoning would experience
higher rates of asthma or wheezing than those without lead poisoning. This
study examines that hypothesis.
SUBJECTS AND METHODS
A matched case-control study was conducted, involving retrospective
review of BLLs and medical records. A goal of 100 subjects in each group was
set to provide 80% power and 95% confidence of detecting a difference in the
occurrence of asthma symptoms between groups of 20% and 40%.
SUBJECTS
The medical records of children receiving pediatric care at a single
Chicago inner-city health center were selected for review based on BLLs recorded
in a tracking database initially established in December 1996 and continually
updated. Variables in the database included child's name, medical record number,
sex, date of birth, address, and primary language and the dates and results
of blood lead analyses performed since December 1996. In November 1999, the
tracking database was reviewed, and 2 groups of subjects with BLLs obtained
at younger than 8 years were determined. First, subjects with any BLL of 25
µg/dL or higher (1.2 µmol/L) (BLL25 group) since December
1996 were determined, and their medical records were reviewed. This BLL was
chosen because it is the action level for environmental investigation in Illinois.
The first BLL25 in the child's medical record was defined as the diagnostic
BLL. The child's age at the diagnostic BLL was computed and used in the matching
process. Data were extracted if the complete medical record was available
and the child had received follow-up after the BLL25 was obtained. Twelve
potential subjects with BLL25 did not meet these criteria. Data from 101 subjects
with BLL25 were reviewed and included.
Next, subjects with an initial tracking database BLL lower than 5 µg/dL
(<0.2 µmol/L) (BLL5 group) and no subsequent BLLs of 10 µg/dL
or more (0.5 µmol/L) were determined. The initial tracking database
BLL5 was defined as the diagnostic BLL for this group. Children were ranked
by age at diagnostic BLL within sex and primary-language groups. Subjects
with BLL5 were randomly matched 1-to-1 to subjects in the BLL25 group on sex,
primary language, and age at diagnostic BLL (within 6 months for subjects
<2 years or within 12 months for subjects 2 years). Among potentially
eligible subjects, 13 with BLL5 selected during randomization were eliminated
owing to an unavailable record. In these cases, a second record was selected
and reviewed. This study was approved by the Children's Memorial Hospital
Institutional Review Board, Chicago.
The health center has a patient population that is 55% African American
and 42% Hispanic. About 68% of its patients are from families with an income
that is less than 100% of the poverty level. Approximately one third (35%)
of pediatric patients are uninsured, 61% have Medicaid coverage, and 4% have
private insurance. All blood lead specimens obtained at the clinic are obtained
by venous draw. During the first part of the study period, the health center
routinely checked BLLs annually. Since fall 1999, BLL screening at the center
has been conducted at 9, 15, 24, 36, and 48 months of age and as indicated
by risk.
Health center patients are primarily from 2 Chicago neighborhoods, North
and South Lawndale. North Lawndale is 96% non-Hispanic black and South Lawndale
is 85% Hispanic (1990 US census). Chicago Department of Public Health statistics
for 1998 reported that 36% of North Lawndale tested and 17% of South Lawndale
children tested had a BLL of 10 µg/dL or higher (0.5 µmol/L).28 Blood lead analyses were conducted by the Illinois
Department of Public Health Laboratory using atomic absorption spectrophotometry.
MEDICAL RECORD REVIEW
One of us (S.N.M.) reviewed medical records. The following computer
database variables were verified from the medical record: sex, date of birth,
primary language, and BLLs. The medical records were reviewed for child address
obtained at the time of the diagnostic BLL. The entire record was reviewed
for race, diagnosis of asthma, and history of asthma symptoms (defined as
a diagnosis of asthma, a clinical diagnosis of bronchiolitis, or a symptom
report of wheezing).
Health care use was determined by visit counts and immunization status.
Immunization status for each child at the current age was reviewed and compared
with the following schedule, which is based on Centers for Disease Control
and Prevention and Illinois Department of Public Health recommendations.29-30 Children were considered not delayed
if they met the following schedule: aged 9 to 11 months with 3:3:3 (diphtheria
and tetanus toxoids and pertussis, Haemophilus influenzae type B, and inactivated polio vaccines); aged 12 to 23 months with
3:3:3; aged 24 to 71 months with 4:3:1:3 (diphtheria and tetanus toxoids and
pertussis, Haemophilus influenzae type B, measles-mumps-rubella,
and inactivated polio vaccines); and 6 years or older with 5:4:3:2. Additionally,
older children were considered delayed if their immunization status when they
were 24 months old was delayed. Coding decisions on unclear record notations
were reached by consensus opinion with a health center physician (B.R.). Data
from primary care visits at other sites were not available.
The year homes were built was determined from 1999 tax records released
by the Cook County (Illinois) Tax Assessor. Records are available at the Web
site, http://www.newschicago.org (accessed April 2, 2001).
ANALYSIS
Data were analyzed using SAS statistical software (SAS Institute, Cary,
NC). Matched-pairs analyses were conducted and the significance of results
tested using odds ratios (ORs), 95% confidence intervals (CIs),31
and Wilcoxon signed rank tests. P<.05 was considered
significant.
RESULTS
There were 101 subjects with BLL25 and 101 with BLL5 included. As shown
in Table 1, groups did not differ
on age at diagnostic BLL, sex, or use of Spanish as their primary language.
These variables were used in the matching process. Child's age at medical
record review was significantly older for the BLL25 group.
Race was determined for 101 subjects with BLL25 and 90 subjects with
BLL5. Of those whose race was known, the majority of children in both groups
were African American (BLL25, 89 [88%] of 101 vs BLL5, 74 [82%] of 90).
There was no significant between-group difference on diagnosis of asthma
or history of asthma symptoms; 6% of subjects with BLL25 and 11% of subjects
with BLL5 had a diagnosis of asthma (OR, 0.5; 95% CI, 0.2-1.4), and 26% of
subjects with BLL25 and 34% of subjects with BLL5 had a history of asthma
or asthma symptoms (OR, 0.7; 95% CI, 0.4-1.3) documented in the medical record
at the time of review.
Subjects with BLL25 had delayed health care but did not differ on total
number of clinic visits. Of subjects with BLL25, 53% had delayed immunization
vs only 20% of subjects with BLL5 (n = 97 matched pairs; OR, 5.0; 95% CI,
2.5-9.9). Children with BLL5 were more likely than subjects with BLL25 to
initiate care at the clinic as a newborn (median age [range], months, at first
clinic visit: BLL25, 5 [0-91]; BLL5, 0 [0-64]; Wilcoxon P = .003). However, the groups had a similar total number of visits
(median [range], No. of visits: BLL25, 15 [3-54]; BLL5, 15 [3-73]; Wilcoxon P = .09).
The ages of 88 BLL25 homes and 71 BLL5 homes were identified from city
and county tax records. Distribution of the year homes were built is shown
in Figure 1. Of BLL25 homes, 30%,
66%, 2%, and 2% were built before 1900, from 1900 through 1929, from 1930
through 1949, or from 1950 through 1979, respectively. For the BLL5 group,
these percentages were 24%, 61%, 6%, and 10%, respectively. In an analysis
restricted to matched pairs in which both subjects had the year their home
was built identified, BLL25 homes were significantly older than the BLL5 homes
(n = 68 matched pairs; Wilcoxon P = .04).
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Year homes were built for subjects with blood lead levels (BLLs)
of 25 µg/dL or higher (BLL25) and subjects with blood lead levels lower
than 5 µg/dL (BLL5). To convert BLLs to micromoles per liter, multiply
micrograms per deciliter by 0.0483.
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COMMENT
We found no increased likelihood of asthma diagnosis or symptoms among
young children with lead poisoning compared with age-, sex-, and language-matched
children with low BLLs who were attending the same clinic. In both groups,
the prevalence of asthma symptoms among preschool-aged children was high,
as is commonly found in Chicago.
These findings have implications for strategies used to target homes
in the US Department of Housing and Urban Development–funded Healthy
Homes Initiatives. Strategies that target homes based on the presence of children
with lead poisoning are likely to encounter preschool-aged children with asthma
at the expected rate, as determined for that area, and provide services or
repair to older buildings. Strategies that focus on "case" identification
by identifying preschool-aged children with asthma will include more recently
built homes among the group selected for repair. We cannot speculate on whether
lead poisoning is more prevalent among children with asthma because our sample
was not selected to answer that question.
The significance of the lack of comorbidity between lead poisoning and
asthma in this study may be limited by the disparate peak incidences of these
diseases. Other studies report that lead poisoning peaks among preschool-aged
children1 and asthma peaks among school-aged
children.10 Further, asthma symptoms among
preschool-aged children are predictive of ongoing asthma in fewer than 50%
of patients.32-33 Nevertheless,
efforts to provide home remediation to prevent asthma progression may need
to focus on young children at a time when the certainty of asthma progression
is not clear but the certainty of lead poisoning has been established.
A longitudinal prospective study in diverse sites, following subjects
from preschool through school age, may be more effective at demonstrating
a comorbidity between lead poisoning and asthma and would define longer-term
relationships between these diseases. Such a study would overcome limitations
of our study related to retrospective medical record review methods and single-site
enrollment. Confounding variables, including family history of asthma, breastfeeding
history, and exposure to smoking, would also be important to consider. Although
children were matched on age at diagnostic BLL, children in the BLL25 group
were somewhat older than children in the BLL5 group at record review. This
bias would have given children with BLL25 extra opportunities to receive care
for asthma symptoms, something that we did not find to occur.
Children with lead poisoning received less optimal health care than
children with low BLLs and were more likely to have delayed immunizations
and began their care at this clinic at a later age. However, because the numbers
of clinic visits were similar, we do not feel that an underreporting bias
for asthma or asthma symptoms because of lack of access to care at this site
contributed significantly to our inability to detect a significant between-group
difference for these variables. The finding of delayed care reinforces the
difficulty in identifying children with lead poisoning because those who do
not seek care may be at highest risk. Health providers should use all patient
contacts to update immunizations34 and conduct
blood lead screening.35
Although nearly all children in this study resided in homes built before
1950, there was increased risk for lead poisoning among residents of the oldest
homes. Houses in the BLL25 group were significantly older than in the BLL5
group. The increased age of homes among BLL25 subjects is consistent with
the environmental risk factors (eg, household lead) and demographic/social
risk factors (eg, poverty) associated with lead poisoning and is consistent
with previous studies.36-39
In summary, among these young children, there was no significant association
between lead poisoning and asthma diagnosis or asthma symptoms. This may be
owing to disparate peak incidences of these diseases. Further studies of school-aged
children should be conducted to confirm and expand our findings. We did find
that lead poisoning was associated with delayed immunizations, a late start
to pediatric primary care at this clinic, and residence in the oldest houses.
These data should be considered when developing a strategy for entry into
comprehensive home environmental remediation programs.
| What This Study Adds
Asthma and lead poisoning are common in urban areas, and both diseases
have an environmental mechanism. There has been a recent increase in funding
to create environmentally "safe" homes. Determining lead and asthma comorbidity
may contribute to our understanding of the efficiency of comprehensive environmental
remediation investments.
In the sample of children studied, there was no increased likelihood
of asthma diagnosis or symptoms among young children with lead poisoning.
Children with lead poisoning received less timely health care and lived in
older homes. These data may provide information that will guide interventions
aimed at preventing or reducing the severity or impact of lead poisoning and
asthma.
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AUTHOR INFORMATION
Accepted for publication April 26, 2002.
This study was presented in part at the annual meetings of the Midwest
Society for Pediatric Research, Chicago, September 21, 2000, and the Pediatric
Academic Societies, Baltimore, Md, April 28, 2001.
We thank Tianyue Chen, MS, for assistance with data analysis.
Corresponding author: Helen J. Binns, MD, MPH, Children's Memorial
Hospital, 2300 Children's Plaza, Box 208, Chicago, IL 60614 (e-mail: hbinns{at}northwestern.edu).
From the Department of Pediatrics, Hope Children's Hospital, Oak Lawn,
Ill (Dr Myers), Lawndale Christian Health Center, Chicago, Ill (Dr Rowell),
and the Department of Pediatrics, Children's Memorial Hospital, Northwestern
University, Chicago (Dr Binns).
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