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* From the Channing Laboratory (Drs. Celedón, Silverman, and Weiss), Brigham and Women’s Hospital, Harvard Medical School, Boston, MA; Department of Pediatrics (Dr. Soto-Quiros), Hospital Nacional de Niños, San José, Costa Rica; and Department of Clinical Immunology (Dr. Hanson), University ofGöteborg, Göteborg, Sweden.
Correspondence to: Juan C. Celedón, MD, MPH, FCCP, Channing Laboratory, 181 Longwood Ave, Boston, MA 02115; e-mail: juan.celedon{at}channing.harvard.edu
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Abstract |
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Objective: To examine the relation between potential risk factors and childhood asthma in Costa Rica.
Methods: Cross-sectional study of 214 schoolchildren aged 10 to 13 years participating in phase II of the International Study of Asthma and Allergies in Childhood.
Results: After adjustment for age, gender, area of residence, maternal smoking during pregnancy, and airway responsiveness to hypertonic saline solution, sensitization to house dust mites was associated with asthma (odds ratio [OR], 2.2; 95% confidence interval [CI], 1.1 to 4.4; p = 0.02). In the multivariate analysis, parental education no higher than high school (OR, 3.0; 95% CI, 1.4 to 6.4; p < 0.01) and parental history of asthma (OR, 2.6; 95% CI, 1.3 to 5.2; p < 0.01) were also independent predictors of childhood asthma.
Conclusions: Sensitization to house dust mites, low parental education, and parental history of asthma are associated with asthma in Costa Rica.
Key Words: childhood asthma • Costa Rica • International Study of Asthma and Allergies in Childhood
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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A number of epidemiologic studies have identified potential risk factors for childhood asthma, including sensitization to perennial aeroallergens (such as house dust mites),4 5 6 7 parental history of asthma,8 9 infections with respiratory syncytial virus,10 dietary habits,11 in utero smoking,12 residence in urban areas,13 and reduced exposure to other children.14 Although childhood asthma is a major public health problem in Costa Rica, little is known about the factors that may influence the pathogenesis and severity of asthma in this Central American nation. We report our findings among 214 Costa Rican schoolchildren participating in phase II of the ISAAC.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Study Population
In 1998, 75 of 5,000 educational centers registered in Costa
Rica were selected for inclusion in the study by random stratification
for geographic location, including urban and rural areas. Core
questionnaires from phase I of ISAAC15
were sent to the
parents of 1,500 10-year-old children enrolled in these schools, and
1,105 of these questionnaires (73.7%) were completed. Of these 1,105
schoolchildren, 299 had parental reporting of wheezing in the previous
12 months, and a random sample of 174 of these children and a random
sample of 132 of the remaining 806 children were included in this
study.
Procedures
Data were collected between November 1998 and November 1999.
After written informed consent was obtained from the parents of
participating children, the following procedures were carried out in
accordance with protocols from phase II of ISAAC16
: (1)
completion of a standardized questionnaire, including questions on
respiratory and nasal symptoms, respiratory health status, management
of asthma, rhinitis, and eczema, home environment, and family history
of respiratory and allergic illnesses; (2) spirometry; (3) measurement
of airway responsiveness to hypertonic saline solution; (4) skin
testing for reactivity to eight aeroallergens along with a positive and
negative control; and (5) collection of a blood sample for measurement
of serum total IgE.
Spirometry
A spirometer (Compact II; Vitalograph Ltd; Buckinghamshire, UK)
was used to perform spirometry in a standardized manner, with subjects
seated and wearing a noseclip. As many as eight attempts were made by
each participant in order to obtain three acceptable measurements.
Spirometry was performed in accordance with American Thoracic Society
specifications,17
and the higher
FEV1 value from two reproducible measurements
(within 5%) was recorded as the baseline FEV1.
Airway Responsiveness to Hypertonic Saline Solution
Hypertonic saline solution challenge testing, using the ISAAC
protocol,16
was performed in subjects whose
FEV1 was > 75% of predicted. Subjects were
asked to avoid bronchodilator use for at least 4 h before testing,
unless symptoms required bronchodilator treatment. A subject was
categorized as having increased airway responsiveness to hypertonic
saline solution if FEV1 fell by 
15% from
baseline at any time during testing.
Allergy Skin Testing
Skin testing was performed according to the ISAAC phase II
protocol.16
In addition to histamine and saline solution
controls, the following antigens were applied to the skin of the
forearm: Periplanetaria americana (cockroach);
Dermatophagoides pteronyssinus; Dermatophagoides
farinae; dog dander; cat dander; mixed tree pollen; mixed grass
pollen; and Alternaria tenuis. The result of a test was
considered to be positive if the maximum diameter of the wheal was
> 3 mm after subtraction of the negative control.
Measurement of Serum Total IgE
Serum total IgE levels were determined (IMx System; Abbott
Diagnostics; Abbott Park, IL). All values were transformed to a
log10 scale for analysis, in accordance with the
recognized logarithmic distribution of serum total IgE levels in the
general population.18
Definitions of Asthma and Rhinitis
Our definition of asthma was based on an affirmative answer to
the question "Has your child ever been diagnosed by a doctor as
having asthma?," as well as by the presence of one or more of three
respiratory symptoms (ie, current or usual cough without a
cold; wheezing; and nocturnal wheezing or cough) or a history of asthma
attacks during the 12 months preceding completion of the questionnaire.
The presence of allergic rhinitis was determined by affirmative answers
to the questions "Has your child ever had hay fever or a runny or
blocked nose with sneezing and itching when he/she did not have a
cold?" and "Does your child still have these symptoms?"
Definition of Predictor Variables
Sociodemographic variables included the following: age; gender;
parental education, classified according to the highest educational
level (primary or middle school, high school, college, or postgraduate)
attained by either parent; and area of residence (central valley vs
coastal areas). Perinatal and familial factors included the following:
in utero exposure to maternal smoking (yes or no); breast
feeding (yes or no); number of months of breast feeding (< 4 months,
4 to 6 months, or 7 months); history of asthma in at least one
parent (yes or no); birth weight (< 3 lb vs 3 lb); and number of
siblings (0 vs 1 or more siblings).
Statistical Methods
Bivariate relationships between the predictor and outcome
variables were analyzed with 
2 tests for pairs
of categoric variables or with two-tailed t tests for a
categoric and a continuous variable. Stepwise logistic regression was
used to develop the multivariate models. In the final models, we
included those variables that satisfied a change-in-estimate criterion
(ie, 10% in the odds ratio [OR] estimate) or that
were significant at the p < 0.05 level. All of the analyses were
performed with a statistical software package (SAS; SAS Institute;
Cary, NC).
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Results |
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No statistically significant differences in age, gender, parental education, number of siblings, serum total IgE level, or STR to aeroallergens were found between subjects included in the current analysis (n = 214) and those excluded (n = 92). Since the study was designed to enroll approximately 100 asthmatic subjects and 100 control subjects, the prevalence of asthma was predictably higher in subjects included in the current analysis than in those excluded (53.3% vs 8.7%, respectively; p < 0.01).
Table 1 summarizes the main characteristics of study participants. The mean age ± SD of the study subjects was 11.1 ± 0.5 years.
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Discussion |
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A significant number of studies conducted around the world have found an association between parental history of asthma and asthma in children.8 9 19 20 Since this association could result from genetic factors or a shared environment, twin studies have been conducted to separate the relative contributions of genetic and environmental factors to the development of asthma.21 22 23 24 25 Estimates of heritability (the proportion of phenotypic variance attributed to genetic factors) from several twin studies conducted around the world have ranged from 36 to 79%, with the highest values coming from studies that had a more comprehensive phenotypic assessment of asthma.26 Thus, asthma is most likely a complex disease, resulting from the interaction between genetic and environmental factors.
Many epidemiologic studies conducted in countries with a western lifestyle have found an association between sensitization to house dust mites and asthma.4 5 6 7 The concentration of mite allergens and the number of mites found in bed dust collected in Costa Rican homes are very high,27 which likely leads to the sensitization of susceptible children to this allergen. Factors such as high humidity (particularly in coastal areas) and a change in bedding material may be responsible for the high mite infestation of Costa Rican homes. Whereas 50 years ago most mattresses were made of a soft plant that had to be changed frequently (paja), most mattresses in contemporary Costa Rica are made of synthetic materials that allow mite proliferation.
In a study of 499 families living in the Boston metropolitan area, Litonjua and coworkers28 found that low parental education (not higher than high school) was an independent predictor of childhood asthma (OR, 1.5; 95% confidence interval [CI], 1.1 to 2.0) after adjustment for race, household income, area of residence, and other potential confounders. Studies conducted in western countries have also shown an association between low socioeconomic status and asthma severity,29 30 asthma symptoms,29 31 and airway hyperresponsiveness.31 In contrast, earlier studies32 33 from Great Britain found that asthma was more common among subjects of high socioeconomic status. Our findings with regard to parental education and asthma in Costa Rica may be due to greater allergen exposure in poor dwellings, residual confounding by maternal smoking during pregnancy, or selection bias (if parents of nonasthmatic children who lacked a college education were significantly less likely to respond to the initial survey than highly educated parents of nonasthmatic children).
We recognize several limitations to our findings. First, as this is a cross-sectional study, we cannot determine whether, for instance, sensitization to dust mites preceded the development of childhood asthma. Second, because of the relatively small sample size, our statistical power may not have been adequate to detect an association between a particular factor and the outcome of interest.
In Costa Rica, a socially developed Latin American country, independent predictors of childhood asthma include sensitization to house dust mites, parental history of asthma, and low level of parental education. Since most of the Costa Rican population is ethnically homogenous, the current high prevalence of childhood asthma in Costa Rica may be the result of an interaction between lifestyle changes occurring in the last half of the 20th century and yet-unidentified genetic factors.
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Acknowledgements |
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Footnotes |
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Dr. Celedón is supported by National Research Service Award grant No. HL07427 and by a Charles A. King Trust Fellowship Award from the Medical Foundation.
Received for publication December 20, 2000. Accepted for publication April 16, 2001.
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This article has been cited by other articles:
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  N. P. Ly, M. E. Soto-Quiros, L. Avila, G. M. Hunninghake, B. A. Raby, D. Laskey, J. S. Sylvia, and J. C. Celedon Paternal Asthma, Mold Exposure, and Increased Airway Responsiveness Among Children With Asthma in Costa Rica Chest, January 1, 2008; 133(1): 107 - 114. [Abstract] [Full Text] [PDF]
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