risk factors for asthma in school children from ciudad juarez, chihuahua

©2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016

JOURNAL OF ASTHMA

Vol. 40, No. 4, pp. 413–423, 2003

ORIGINAL ARTICLE

Risk Factors for Asthma in School Children from Ciudad Juarez, Chihuahua

Albino Barraza Villarreal, Sc.M.,1,* Luz Helena Sanın Aguirre, M.D., Sc.D.,2

Martha Marıa Tellez Rojo, Sc.M.,1 Marina Lacasana Navarro, Sc.M., Ph.D.,1

Isabelle Romieu, M.D., M.P.H., Sc.D.3

1Instituto Nacional de Salud Publica, Morelos, Mexico2Universidad Autonoma de Chihuahua, Mexico

3Center for Disease Control and Preventions, Pan-American Health Organization,

Washington, D.C., USA

ABSTRACT

Asthma and allergic rhinitis were analyzed in a random sample of school children

(n¼ 6174) residing in Ciudad Juarez, Chihuahua, Mexico. The International Study of

Asthma and Allergies in Childhood methodology was applied through a standardized

questionnaire. The sample was obtained with a bietapic design. Cumulative prevalence

of asthma and wheezing was 6.8% (95% CI 6.2, 7.4) and 20% (95% of CI 19.7, 21.8)

respectively; the prevalence of rhinitis was 5.0% (95% CI 4.5, 5.6). Family history of

asthma odds ratio (OR) 2.33 (95% CI 1.78–3.05), respiratory infection after birth (OR)

3.44 (95% CI 2.76–4.29), and exposure to environmental tobacco (OR) 1.35 (95% CI

1.06–1.68) were the strongest risk factors for asthma and allergic rhinitis. The

multifactorial etiology of asthma and allergic rhinitis was confirmed, as well as the

importance of early exposure to environmental factors.

Key Words: Risk factors; Asthma; Wheezing; Rhinitis; ISAAC; Juarez; Mexico.

INTRODUCTION

Several risk factors can contribute to the increasein the prevalence and incidence of asthma, includingindoor and outdoor pollutants, recurrent respiratoryinfections during the early years of life, and exposureto different aeroallergens (1–3).

Epidemiological studies conducted in differentcountries in the last decades have indicated associa-tions between diverse factors with respiratory symp-toms (cough, phlegm, wheezing) and an increase inthe prevalence and severity of asthma and other aller-gic diseases within the children’s population (4–6).Maternal smoking is a predominant risk factor in

*Correspondence: Albino Barraza Villarreal, Instituto Nacional de Salud Publica, Av. Universidad 655, Col. Sta. Ma.

Ahuacatitlan, C.P. 62508, Cuernavaca, Morelos, Mexico; Fax: (52777)311-11-48; E-mail: [email protected].

413

DOI: 10.1081/JAS-120018711 0277-0903 (Print); 1532-4303 (Online)

Copyright & 2003 by Marcel Dekker, Inc. www.dekker.com

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many studies (7–9); Strachan and Cook in 1998reported that parental smoking is responsible forwheezing bronchitis among nonatopic children andis an important factor for the emergence of manyrespiratory illnesses in children diagnosed withasthma (10). These factors can also increase morbid-ity and mortality because of this pathology. However,the relative importance of interaction of genetic andenvironmental factors in the development of asthmahas not yet been clarified. The epidemiological inves-tigations conducted recently have underlined thenecessity to generate new hypotheses that wouldhelp to clarify possible causes contributing to theincrease of the prevalence of asthma in differenttypes of populations around the world.

Asthma and allergic rhinitis are illnesses withmultifactorial etiology. Genetic factors are implicatedin the onset of bronchial hyperreactivity. In addition,these factors appear to determine the level of reactiv-ity or the predisposition to acquire the disease andthe presence of atopy (11–14). Currently, no specificetiology has been established that accounts forclinical characteristics and particular pathologies,immunological mechanisms, nor the environmentalfactors that influence the development of asthmaand allergic diseases (15–19).

In this article, risk factors for asthma and allergicrhinitis are examined in a random sampling ofchildren participating in a study on the prevalenceof allergic diseases from Juarez, Chihuahua, Mexico.

MATERIAL AND METHODS

The study was conducted in the metropolitanarea of Juarez, Chihuahua, Mexico, using the meth-odology proposed by ISAAC (International Study ofAsthma and Allergies in Childhood) (20).

The investigation was planned in accordancewith potential areas of pollution within the city,which was divided into three major strata based onair pollution data and expert assessment. Strata 1corresponded to the center of the city and was con-sidered the most polluted zone, based on particulatematter data, as well as the area with most motorvehicle traffic; strata 2 covered the largest zone ofthe city and was considered the area with mediumair pollution levels; and strata 3 corresponded tothe surrounding area of the city and was consideredthe least polluted zone.

The sample size was calculated to be able to suf-ficiently detect variations in the prevalence amongcities and in the prevalence of the severity of the

studied cases—between 3% and 5% respectively,according the ISAAC specifications and given themulticenter character of the study. A randomsample of 7200 school-aged children (6 to 8 yearsand 11 to 14 years) was chosen, obtaining approxi-mately 3000 children for each study group, plus anadditional 20% to prevent losses.

Data Collection

In collaboration with the Ministry of PublicEducation (SEP) in Chihuahua, Mexico, we obtainedgeneral information on elementary schools, whichallowed us to elaborate the database. The initialframework included 335 elementary schools. Thesampling fraction was assigned using proportionalallocation. The sample included 53 schools thatwere listed by total students in the first and sixthyears of elementary school.

The questionnaire included the basic ISAACquestions on asthma, rhinitis, and eczema, which per-mits recognition of prevalence by medical diagnosisand by the presence of symptoms of these diseases, aswell as general information on medical history andpotential risk factors for asthma and other allergicdiseases.

Data Analysis

First, a descriptive data analysis was conductedto understand the characteristics of the study group.A stratified analysis was run according to age group,gender, family history of asthma, and strata air pol-lution. To detect the main predictors of asthma andallergic rhinitis, a bivariate analysis was conductedusing logistic regression models. We defined the bestmodel by dropping covariates one by one from asaturated model that included all variables. Ourfinal multivariate model included all-important pre-dictors with a statistically significant association( p<0.05). The results were expressed in odds ratios(OR), calculated using methods of maximum likeli-hood with their corresponding confidence intervals of95% (95% CI). To determine the reproducibility ofour questionnaire we used kappa statistics comparingresponses to the questionnaire applied twice weekly.

The operational definitions used for asthmawere: current wheezing, wheezing without flu orcold in the last 12 months, and three or more episodesof wheezing in the last 12 months. For rhinitis, twodefinitions were considered: rhinitis without flu or

414 Barraza Villarreal et al.

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cold in the last 12 months and rhinitis and ocularsymptoms. Genetics is a factor considered as indicat-ing predisposition in the development of these ill-nesses; for the purposes of this study, a child wasconsidered atopic if the father, mother, or any siblinghad a history of asthma. Respiratory problem atbirth was defined as any type of respiratory problemthat needed medical attention, and respiratory infec-tion at birth was defined as any type of respiratoryinfection accompanied by fever and that needed med-ical attention. All the analyses and the sample sizecalculation were performed using Stata (StataStatistical Software, Release 5.0, Stata Corporation,College Station, TX) (21).

RESULTS

Among 6749 eligible children, 6200 were activelyenrolled, of which only 26 were excluded from theanalysis because they did not belong to the estab-lished age groups, leaving a response rate of 92%.A total of 3082 of the participants were male and3092 female. A total of 92.5% of the schools includedin the study were public schools and 7.5% were pri-vate schools. Regarding the level of education, 2.2%of the mothers had no education, 49.1% had com-pleted elementary level education, 32.8% reached thesecondary school level, and 8.2% achieved aprofessional level (Table 1).

The prevalence of asthma and rhinitis by medicaldiagnosis and symptoms are shown in Table 2. Theoverall prevalence of current wheezing was 7.9%.Higher prevalence was observed in the younger agegroup (9.7% vs. 5.8%). The overall prevalence ofallergic rhinitis including ocular symptoms was16.6% and was slightly higher in the younger agegroup (17.0% vs. 16.1%).

In the bivariate analysis, several factors wererelated to the risk of wheezing and rhinitis, includingyounger age, family history of asthma, older age of themother, exposure to tobacco in utero, respiratoryproblems after birth, respiratory infections afterbirth, exposure to tobacco during the first 2 years oflife, presence of cockroaches within the home, andhumidity in the home. Breast-feeding for more than6 months was a protective factor against wheezing ascompared with children who never breastfed (Table 3).A total of 8.1 % of children had a family history ofasthma; among these children, the prevalence ofasthma and allergic rhinitis (as indicated by medicaldiagnosis) was greater (21.6% and 7.8%, respectively)and an important risk factor for this illness.

Smoking during pregnancy was a significant riskfactor in the case of asthma, defined as currentwheezing (OR 1.79, 95% CI 1.32–2.43) and morethan three episodes of wheezing (OR 2.92, 95% CI1.67–5.24). The sample showed that 6.7% of themothers smoked while pregnant. For rhinitiswithout flu or cold, this was also shown to be astatistically significant risk factor (OR 1.34, 95% CI1.09–1.67).

Twenty-one percent of the mothers gave birth atthe age of 19 or younger and only 4.3% gave birthafter age 34. The bivariate analysis showed thathaving a child after age 30 increased significantlythe risk for current wheezing, using as reference theage 20 group (OR 1.35, 95% CI 1.03–1.77). In thecase of rhinitis without flu, it was found that givingbirth between age 25 and 29 was a statisticallysignificant risk (OR 1.23, 95% CI 1.05–1.44).

Approximately 65% of the mothers breast-fedtheir children whereas 36% reported to have breast-fed their children for at least 6 months. Breast-feedingprovided a protective effect that was statistically sig-nificant for more than 6 months (OR 0.69, 95% CI0.54–0.88) using the operational definition for wheez-ing in the last 12 months. There was no statisticallysignificant association for rhinitis based on both itsoperational definitions.

Table 1. Frequency of sociodemographic variables.

Variable na %

Sex

Male 3082 49.91

Female 3092 50.08

Age

6–8 years 3390 54.91

11–14 years 2784 45.09

Mother’s education

None 133 2.20

Elementary 2987 49.15

Middle 1994 32.81

High 467 7.68

Professional 496 8.16

Father’s education

None 168 2.88

Elementary 2453 42.00

Middle 1726 29.55

High 690 11.82

Professional 803 13.75

Type of school

Public 49 92.54

Private 4 7.53

an varies from 5840 to 6174 within the studied variables.

Risk Factors for Asthma in Children from Juarez 415

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Of the sample population, 7.9% reported sometype of respiratory problem after birth, and this wasshown to be a statistically significant risk factor forthe following illnesses: current wheezing (OR 3.03,95% CI 2.35–3.89), wheezing without flu or cold(OR 4.02, 95% CI 2.74–5.90), and more than threeepisodes of wheezing (OR 2.49, 95% CI 1.39–4.46).For rhinitis without flu or cold (OR 1.78, 95% CI1.47–2.16), rhinitis plus ocular symptoms (OR 1.97,95% CI 1.58–2.43), and for asthma and rhinitis, thisfactor was observed to be important inasmuch as thedefinition was more specific.

The same trend was observed for respiratoryinfection after birth. The sample showed that 6.5%presented respiratory infections before 6 months ofage, and that 3.1% presented infections between 6and 12 months. Respiratory infections constitute animportant risk factor for current wheezing (OR 3.81,95% CI 3.08–4.73), wheezing without a cold (OR3.84, 95% CI 2.70–5.47), more than three episodesof wheezing (OR 5.22, 95% CI 3.32–8.21), rhinitiswithout flu or cold (OR 1.48, 95% CI 1.25–1.74),and for rhinitis plus ocular symptoms (OR 1.83,95% CI 1.52–2.21).

Thirty-three percent of the parents smoked in thepresence of the child; 18.5% of these smoked fewerthan 3 cigarettes per day, 11.0% smoked 3–10cigarettes, and 2.1% smoked more than 11 cigarettesper day. Passive smoking represents a significant risk

factor for asthma and rhinitis based on its differentoperational definitions: current wheezing (OR 1.35,95% CI 1.12–1.64), wheezing without a cold (OR1.32, 95% CI 0.95–1.84), more than three episodesof wheezing (OR 1.86, 95% CI 1.20–2.88), rhinitiswithout flu or cold (OR 1.23, see 95% CI1.10–1.38), and rhinitis plus ocular symptoms (OR1.21, 95% CI 1.05–1.40) (see Table 3).

Exposure to passive smoking was evaluated forthe first 2 years of the life of the child, and was foundto be strongly associated to asthma for its three defi-nitions: OR 1.60, 95% CI 1.30–2.0; (OR 1.63, 95%CI 1.13–2.36; and OR 2.02, 95% CI 1.25–3.24,respectively. In the case of rhinitis and both its defini-tions, passive smoking was also found to be animportant risk factor.

Approximately 55% of the fathers mentionedhaving had domestic animals during the last 12months; the animal most frequently mentioned wasa dog, followed by a cat. These animals represented arisk factor for rhinitis without flu or cold (OR 1.19,95% CI 1.06–1.33).

Thirty-three percent of the parents declaredthe presence of carpeting or rugs in the child’sbedroom. The rug or carpeting behaved as arisk factor for wheezing without a cold (OR 1.62,95% CI 1.17–2.23), more than three episodesof wheezing (OR 1.74, 95% CI 1.12–2.70), rhinitiswithout flu (OR 1.23, 95% CI 1.09–1.38), and for

Table 2. Prevalence of asthma and rhinitis by medical diagnosis and by symptoms among school children.

Variable

All ages 6–8 yr 11–14 yr

na % (95% CIb) na % (95% CIb) na % (95% CIb)

Medical diagnosis

Asthmac 264 4.3 (3.8–4.8) 143 4.2 (3.5–4.9) 121 4.4 (3.65–5.2)

Asthmatic bronchitisc 302 4.9 (4.4–5.5) 169 5.0 (4.3–5.8) 133 4.8 (4.1–5.7)

Rhinitisc 308 5.0 (4.5–5.6) 158 4.7 (4.0–5.7) 150 5.4 (4.6–6.3)

Asthma and/or asthmatic bronchitisc 419 6.8 (6.2–7.4) 227 6.7 (5.9–7.6) 192 7.4 (6.4–8.4)

By symptom reports

Wheezing at some timec 1271 20.7 (19.7–21.8) 759 22.4 (21.0–24.0) 512 18.4 (17–20)e

Current wheezingd 491 7.9 (7.3–8.6) 329 9.7 (8.7–11.0) 162 5.8 (5.0–6.8)e

Wheezing after exercised 291 4.7 (4.2–5.3) 174 5.2 (4.4–5.9) 116 4.2 (3.5–5.0)e

Wheezing without flu or coldd 153 2.5 (2.1–2.9) 101 2.9 (2.4–3.6) 52 1.9 (1.4–2.5)e

More than 3 episodes of wheezingd 99 1.6 (1.3–1.9) 55 1.6 (1.2–2.1) 44 1.6 (1.2–2.2)e

Nasal symptoms without flud 1772 28.8 (28.0–30.0) 974 28.8 (27.3–30.4) 798 29.0 (27.0–31.0)e

Nasal symptoms plus oculard 1016 16.6 (15.6–17.5) 572 17.0 (15.7–18.2) 444 16.1 (15–17.4)e

an¼ number of children.b95% CI¼ 95% confidence interval.cAccumulated prevalence.dCurrent prevalence.ep<0.001 (calculated with Pearson chi2).


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rhinitis plus ocular symptoms (OR 1.22, 95% CI1.06–1.40).

Nine point nine percent of the parents mentionedhaving mold or humidity within the home, and thiswas a factor strongly associated to the followingillnesses: current wheezing (OR 1.99, 95% CI1.55–2.57), wheezing without a cold (OR 2.12, 95%CI 1.39–3.22), more than three episodes of wheezing(OR 2.25, 95% CI 1.30–3.91), rhinitis without flu orcold (OR 1.61, 95% CI 1.36–1.92), and rhinitis plusocular symptoms (OR 1.94, 95% CI 1.60–2.36).

Another of the variables that plays a very impor-tant role as a risk factor for these illnesses was thepresence of cockroaches within the home; this wastrue for current wheezing (OR 1.80, 95% CI1.48–2.19), more than three episodes of wheezing(OR 1.72, 95% CI 1.08–2.74), rhinitis without flu orcold (OR 1.15, 95% CI 1.03–1.30), and rhinitis plusocular symptoms (OR 1.15, 95% CI 1.03–1.29); in allcases, the presence of cockroaches was statisticallysignificant.

In the multivariate analysis, the only factors thatremain significant predictors of current wheezingwere younger age (OR 1.67, 95% CI 1.36–2.05),family history of asthma (OR 2.33, 95% CI1.78–3.0), respiratory infection at birth (OR, 3.4495% CI 2.76–4.29), and exposure to tobacco duringthe first 2 years of life (OR 1.34, 95% CI 1.06–1.68)(Table 4).

For rhinitis, the model showed that rhinitis basedon its two operational definitions had almost thesame predictors as asthma; having rugs or carpetswithin the home was an additional predictor for rhi-nitis without flu or cold during the last 12 months(OR 1.17, 95% CI 1.03–1.32); for rhinitis plusocular symptoms during the last 12 months, the pre-sence of cockroaches within the home was anotherimportant predictor (OR 1.28, 95% CI 1.11–1.47)(Table 5).

DISCUSSION

This investigation is the second of its kind con-ducted in Mexico. The previous study was conductedin Cuernavaca, Morelos, to determine the risk factorsassociated with asthma and allergic rhinitis within theschool population through the same standardizedquestionnaire. Other studies conducted in Mexicowith different methodologies cannot be readilycompared with the present results (22–24).

Several longitudinal studies have identified differ-ent risk factors for asthma in children; nevertheless,

the complex interaction between environmental andgenetic factors and the different phenotypes ofasthma according to age are not clearly understood.Our findings confirm that asthma is more prevalent inthe group ages 6–8 years, which is consistent with thereports in literature (6,19), and that this same agegroup is where the severity of the illness is observedmore. We also observed that the prevalence ofasthma and rhinitis was significantly greater inchildren with a family history of asthma, whichconstituted a strong predictor in all of the studiedillnesses (25–28).

As observed in other studies (29–34) familyhistory of asthma has a strong risk factor for bothasthma and allergic rhinitis. In addition, we con-ducted a stratified analysis comparing children withand without family history of asthma and observedthat environmental factors played a strong roleamong children without a family history, suggestingthat environmental factors may play a major role inchildren without genetic predisposition. This wasclear when we adjust for symptom severity in whichrespiratory infections were a much greater risk factorin children without a pertinent family history. If, asindicated, it is impossible to correct the geneticburden, we can at least modify the important rolethat environmental factors play as predictors, and,as a result, diminish the presence and severity of thestudied diseases.

Another strong factor associated to these twoillnesses was the presence of respiratory infectionbefore 1 year of age. Studies have confirmed thatrespiratory infection before age 1 not only favorsthe presence of bronchial hyperreactivity, but also isrelated to a diminishing of lung function during ado-lescence and to chronic obstructive illness duringadult life (35). However, we did not have informationon the type of infection, and there is still controversyon the role of viral and bacterial infection on theincidence of children asthma.

Exposure to passive smoking during the first 2years of life appears to be a major risk factor forwheezing and allergic rhinitis, even more thansmoking during pregnancy, as shown in our finalmultivariate models. In this aspect, special atten-tion should be paid to smoking, which hasincreased in recent years and that includes ever-younger age groups. Smoking increases the contactbetween allergens and immunocompetent cells,and possibly reflects an abnormal functioningof the respiratory muscles induced by inhaledpollutants. It has been observed that tobacco pro-vokes a greater bronchial hyperreactivity when


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Table

3.

Risk

fact

ors

for

childhood

ast

hm

aand

rhin

itis,biv

ariate

analy

sis.

Variable

n

Whee

zing

last

12

month

s

Whee

zing

without

aco

ld

More

than

3ep

isodes

of

whee

zing

Rhin

itis

without

flu

or

cold

last

12

month

s

Rhin

itis

plu

socu

lar

sym

pto

ms

last

12

month

s

OR

a95%

CIb

OR

a95%

CIb

OR

a95%

CIb

OR

a95%

CIb

OR

a95%

CIb

Aged 1

1–14

2784

1.0

1.0

1.0

1.0

1.0

6–8

3390

1.7

3(1

.42–2.1

1)

1.6

1(1

.15–2.2

6)

1.1

0(0

.71–1.7

1)

1.0

0(0

.89–1.1

2)

1.0

6(0

.93–1.2

2)

Type

of

schoold

Publicc

5796

1.0

1.0

1.0

1.0

1.0

Private

378

1.0

1(0

.68–1.4

8)

1.3

3(0

.73–2.4

2)

0.5

8(0

.18–1.8

5)

1.4

9(1

.20–1.8

5)

0.9

7(0

.73–1.2

9)

Fam

ily

histo

ryof

ast

hm

ad

No

c5671

1.0

1.0

1.0

1.0

1.0

Yes

503

2.5

8(2

.00–3.3

4)

2.7

3(1

.80–4.1

4)

3.2

4(1

.90–5.1

1)

2.0

4(1

.69–2.4

5)

1.4

5(1

.15–1.8

1)

Moth

er’s

age

<20

yea

rsc

1690

1.0

1.0

1.0

1.0

1.0

21–24

yr

1626

1.0

1(0

.78–1.3

2)

0.9

8(0

.62–1.5

4)

0.8

3(0

.44–1.5

9)

1.0

3(0

.89–1.2

1)

0.9

7(0

.81–1.1

7)

25–29

yr

1460

1.2

1(0

.93–1.5

7)

1.0

7(0

.68–1.6

9)

1.3

2(0

.73–2.3

9)

1.2

3(1

.05–1.4

4)

1.0

8(0

89–1.3

0)

>¼

30

yr

1085

1.3

5(1

.03–1.7

7)

1.3

3(0

.84–2.1

3)

1.4

2(0

.76–2.6

5)

1.0

2(0

.86–1.2

1)

0.9

2(0

.74–1.1

3)

Moth

er’s

educa

tion

None

133

1.3

5(0

.78–1.3

2)

0.8

7(0

.27–2.8

0)

0.8

4(0

.52–1.3

7)

0.9

3(0

63–1.3

9)

1.2

5(0

.80–1.9

4)

Ele

men

tary

c2987

1.0

1.0

1.0

1.0

1.0

Mid

dle

1994

0.8

0(0

.65–1.0

2)

0.8

1(0

.56–1.1

9)

0.3

9(0

.17–0.9

4)

1.0

1(0

.89–1.2

1)

0.9

3(0

.80–1.0

9)

Hig

hsc

hoolor

more

963

0.8

6(0

.65–1.1

4)

1.0

4(0

.67–1.6

5)

1.9

7(0

.70–5.5

6)

1.4

0(1

.20–1.6

4)

1.2

5(1

.01–1.4

7)

Sm

okin

gduring

pre

gnancy

d

No

c5705

1.0

1.0

1.0

1.0

1.0

Yes

412

1.7

9(1

.32–2.4

3)

1.5

2(0

.89–2.6

2)

2.9

2(1

.67–5.2

4)

1.3

4(1

.09–1.6

7)

1.2

5(0

.97–1.6

1)

Tim

ebre

ast

-fee

din

g

Nev

erc

2143

1.0

1.0

1.0

1.0

1.0

Les

sth

an

2m

onth

s689

0.9

6(0

.71–1.3

0)

1.1

1(0

.65–1.8

9)

0.7

0(0

.31–1.6

0)

1.0

1(0

.84–1.2

2)

1.1

1(0

.89–1.4

0)

2–6

month

s1578

0.9

2(0

.73–1.6

7)

0.9

1(0

.59–1.4

1)

1.1

4(0

.67–1.9

3)

0.9

3(0

.81–1.0

8)

0.9

1(0

.77–1.1

0)

More

than

6m

onth

s1738

0.6

9(0

.54–0.8

8)

0.9

7(0

.64–1.4

7)

0.7

2(0

.40–1.2

8)

0.9

4(0

.82–1.0

9)

1.0

4(0

.87–1.2

3)


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Res

pirato

rypro

ble

ms

atbirth

d

No

c5614

1.0

1.0

1.0

1.0

1.0

Yes

483

3.0

3(2

.35–3.8

9)

4.0

2(2

.74–5.9

0)

2.4

9(1

.39–4.4

6)

1.7

8(1

.47–2.1

6)

1.9

7(1

.58–2.4

3)

Res

pirato

ryin

fect

ion

after

birth

d

No

c5382

1.0

1.0

1.0

1.0

1.0

Yes

699

3.8

1(3

.08–4.7

3)

3.8

4(2

.70–5.4

7)

5.2

2(3

.32–8.1

2)

1.4

8(1

.25–1.7

4)

1.8

3(1

.52–2.2

1)

Pass

ive

Sm

okin

gd

No

c4115

1.0

1.0

1.0

1.0

1.0

Yes

2026

1.3

5(1

.12–1.6

4)

1.3

2(0

.95–1.8

4)

1.8

6(1

.20–2.8

8)

1.2

3(1

.10–1.3

8)

1.2

1(1

.05–1.4

0)

Anim

als

inhom

ed

No

c2727

1.0

1.0

1.0

1.0

1.0

Yes

3441

1.1

4(0

.95–1.3

8)

1.2

0(0

.86–1.6

6)

1.7

8(0

.75–1.8

4)

1.1

9(1

.06–1.3

3)

1.1

4(0

.99–1.3

1)

Carp

ets

and

rugsd

No

c4095

1.0

1.0

1.0

1.0

1.0

Yes

2051

1.1

7(0

.97–1.4

2)

1.6

2(1

.17–2.2

3)

1.7

4(1

.12–2.7

0)

1.2

3(1

.09–1.3

8)

1.2

2(1

.06–1.4

0)

Hum

idity

inhom

ed

No

c5228

1.0

1.0

1.0

1.0

1.0

Yes

607

1.9

9(1

.55–2.5

7)

2.1

2(1

.39–3.2

2)

2.2

5(1

.30–3.9

1)

1.6

1(1

.36–1.9

2)

1.9

4(1

.60–2.3

6)

Str

atu

m

11564

0.9

0(0

.58–1.4

1)

0.7

7(0

.38–1.5

8)

0.9

8(0

.33–2.9

1)

1.1

5(0

.88–1.5

1)

1.0

9(0

.79–1.5

1)

24271

1.1

0(0

.73–1.6

6)

0.8

5(0

.44–1.6

4)

1.2

0(0

.43–3.3

2)

1.1

9(0

.93–1.5

3)

0.9

1(0

.78–1.4

4)

3c

339

1.0

1.0

1.0

1.0

1.0

Exposu

reto

tobacc

o

firs

t2

yea

rsof

life

d

No

c5024

1.0

1.0

1.0

1.0

1.0

Yes

1107

1.6

0(1

.30–2.0

)1.6

3(1

.13–2.3

6)

2.0

2(1

.25–3.2

4)

1.4

5(1

.26–1.6

6)

1.4

4(1

.26–1.6

6)

Cock

roach

esd

No

c2779

1.0

1.0

1.0

1.0

1.0

Yes

3257

1.8

0(1

.48–2.1

9)

1.2

1(0

.87–1.6

8)

1.7

2(1

.08–2.7

4)

1.1

5(1

.03–1.3

0)

1.1

5(1

.03–1.2

9)

aO

R¼

odds

ratio.

b95%

CI¼

95%

confiden

cein

terv

al.

cR

efer

ence

.dD

ichoto

my

variable

s.


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Table 5. Risk factors for childhood asthma, multivariate analysis.

Variable n

Wheezing last 12 months Wheezing without a cold

More than 3 episodes

of wheezing

ORa (95% CId) ORb (95% CId) ORc (95% CId)

Family history of asthma

Yes 503 2.33 (1.78–3.05) 2.37 (1.54–3.66) 2.62 (1.53–4.53)

No 5671 1.00 1.00 1.00

Respiratory infection after birth

Yes 699 3.44 (2.76–4.29) 2.45 (1.50–4.01) 4.64 (2.94–7.35)

No 5382 1.00 1.00 1.00

Exposure to tobacco

first 2 years of life

Yes 1107 1.35 (1.06–1.68) 1.54 (1.07–2.26) 1.66 (1.02–2.72)

No 5024 1.00 1.00 1.00

Age group

6–8 3390 1.67 (1.36–2.05) 1.60 (1.13–2.27) 1.02 (0.62–1.52)

11–14 2784 1.00 1.00 1.00

aOR¼Odds ratio adjusted for cockroaches, humidity in home, and breast-feeding; all variables are included simultaneously

in the model.bOR¼Odds ratio adjusted for presence of carpeting and respiratory problems after birth; all variables are included simulta-

neously in the model.cOR¼Odds ratio adjusted for presence of carpeting and humidity in home; all variables are included simultaneously in the

model.d95% CI¼ 95% confidence interval.

Table 4. Risk factors for childhood rhinitis, multivariate analysis.

Variable n

Rhinitis without flu or

cold last 12 months

Rhinitis plus ocular symptoms

last 12 months

ORa (95% CIc) ORb (95% CIc)

Family history of asthmad

Yes 303 1.86 (1.54–2.56) 1.33 (1.05–1.68)

No 5671 1.00 1.00

Respiratory problems after birthd

Yes 483 1.65 (1.36–2.05) 1.53 (1.15–2.05)

No 5614 1.00 1.00

Exposure to tobacco first

2 years of lifed

Yes 1107 1.39 (1.21–1.60) 1.34 (1.12–1.58)

No 5024 1.00 1.00

Carpeting/rugsd

Yes 2051 1.17 (1.03–1.32) 1.21 (1.05–2.14)

No 4095 1.00 1.00

Humidity in homed

Yes 607 1.50 (1.25–1.78) 1.74 (1.42–2.14)

No 5228 1.00 1.00

aOR¼Odds ratio adjusted by type of school, all variables are included simultaneously in the model.bOR¼Odds ratio adjusted by respiratory infection after birth and presence of cockroaches in home, all

variables are included simultaneously in the model.c95% CI¼ 95% confidence interval.


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comparing subjects who smoke with nonsmokingsubjects (9).

Humidity or mold within the home constitutedanother risk factor strongly associated to these sick-nesses. Humidity and a warm climate influenced theresults in two ways. Both favored the development ofmites, which grow well during warm seasons with alevel of relative humidity around 70–80% as well asthe growth of mold. Both mites and molds can triggerasthma and rhinitis crises in children (16).

Our study has limitations that need to beaddressed. It is important to consider the possibilityof selection and information bias given that peoplewith children suffering from one of the studied prob-lems might tend to be more willing to participate orto provide more information related to the illness oftheir child. To evaluate a potential selection bias, acharacterization of losses was made through theapplication of a shorter questionnaire to the childrenthat did not return their questionnaire. No significantdifference was observed with regard to general char-acteristics and symptoms prevalence. In our study,the response rate was 92% (6174 vs. 6749), whichdiminishes considerably the possibility of any kindof bias. Because this questionnaire was autoadminis-tered and responses rely in many instances on thememory of the subjects, misclassification might haveoccurred. However, to classify a subject as asthmatic,one question alone was not considered, but rather theresponses to various questions posed in different waysto define the sicknesses. This process increases thevalidity of the studies. In addition, it is unlikelythat parents are aware of the relation between therisk factors studied and the prevalence of asthmaand rhinitis; therefore, the misclassification is likelyto be random and to underestimate the associationobserved.

To verify the reproducibility of the instrument,the questionnaire was applied on two occasionsweekly to a subsample of 85 schoolchildren. A goodreproducibility was observed, the kappa statisticsranging from 0.67 to 1.00.

In conclusion, among the risk factors moststrongly associated with asthma and allergic rhinitiswe found: family history of asthma, respiratoryinfection after birth, and passive smoking duringthe first 2 years of the life of the child. In addition,the presence of rugs at home and of humidity wasrelated to the risk of allergic rhinitis. These confirmthe multifactorial etiological character of these ill-nesses and the importance of interventions todecrease environmental exposures. In addition, thisstudy provides a baseline to evaluate the change of

prevalence in time and the impact of environmentalinterventions.

ACKNOWLEDGMENTS

This study was supported by the National Centerfor Environmental Health, the Center for DiseaseControl and Preventions and the Pan-AmericanHealth Organization (NCEH/CDC/PAHO).

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risk factors for asthma in school children from ciudad juarez, chihuahua

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