Childhood asthma and the indoor environment in a subtropical area

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DOI 10.1378/chest.114.2.393 1998;114;393-397

Chest

Chun-Yuh Yang, Meng-Chiao Lin and Kuang-Chi Hwang

Environment in a Subtropical Area

Childhood Asthma and the Indoor

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(2)

Childhood Asthma and the Indoor

Environment

in

a

Subtropical

Area'

Chun-Yuh

Yang,

PhD,

MPH;

Meng-Chiao

Lin, MD, MPH; and

Kuang-Chi

Hwang,

MD

Study

objectives:

The

objective

of this

study

is to examine the

relationship

between indoor environmental factors andchildhoodasthmain a

subtropical

area.

Design:

A case-control

study

was

performed

using participants

of a

prevalence

survey that

included 165 schoolchildren withasthma and 165 age-and

gender-matched

control

subjects.

Setting:

The

study

was confined to 4,164 schoolchildren

aged

6 to 12 years

attending eight

primary

schoolsin

Kaohsiung

County

rural

municipalities

who

participated

ina

prevalence

study

concerning

the healtheffects of the indoorenvironment.

Participants:

Cases

(n=165)

were defined as children with current asthma confirmed

by

a

physician.

Control

subjects

(n=165)were selected from thesame school and class and matched

for age and

gender,

and

they

didnothavea

diagnosis

of

asthma,

history

of

physician-confirmed

atopic

diseases,

persistent

wheezing,

cough,

or

phlegm,

or

reported

chest

illness,

pneumonia,

orbronchitis.

Measurementsand results: Information

regarding

the home environmentwasobtained

using

a

structuredwritten

questionnaire,

completed by

theparents of the children. Of the many indoor environmental factors includedin this

study, only

home

dampness

showedan associationwith

asthma

(odds ratio=2.65).

Conclusions:Weconclude that

dampness

inthehomeisanew

public

healthissuein

subtropical

areas.

(CHEST

1998;

114:393-397)

Keywords: asthma;case-control

study;

dampness;

indoorenvironment

Abbreviations: CI=confidenceinterval; OR=oddsratio

4

sthma,

which is an

important

medical

problem

^*-worldwide,

is the most common chronic disease

among

pediatric

patients.

It often leads to

costly

treatment,

disability,

and school absence.1-2 The

prevalence

of asthma in

developing

countries has increasedinrecent

years.3

The

prevalence

of asthma

in schoolchildren in

Taipei

increased from 1.3% in 1974to5.1%in 19854andto 10.8%in 1994

(unpub¬

lished

data;

K.H.

Hsieh;

NationalTaiwan

University

Hospital;

1994).

Asthma is also the most common

lung

disease

associatedwith indoorair

pollution.5

Most

people

in

subtropical

areas

spend

much oftheir life

indoors,

and concern about the health effects of the indoor

environmenthas been

growing

in recent

years.6

The *Fromthe SchoolofPublicHealth,

Kaohsiung

Medical

College,

Kaohsiung,

Taiwan, ROC.

Supported

inpart

by

agrantfrom the NationalScienceCouncil,

ExecutiveYuan, Taiwan(NSC-84-2621-P-037-001).

ManuscriptreceivedOctober21,1997;revisionacceptedJanuary

8, 1998.

Correspondence to: Chun-Yuh Yang, MD, School of Public Health,

Kaohsiung

Medical College, 100 Shih-Chuan 1st RD,

Kaohsiung, Taiwan 80708;email:chunyuh@cc.kmc.edu.tw

indoor environment in

developing

countries is sub¬

jected

to

pollutants

from numerous sources.7 In

1994,

we conducted a

large questionnaire-based

study

ofthe

respiratory

health effects of the indoor

environment inthe ruralareasof

Kaohsiung

County,

which has a

subtropical

climate. This article focuses onthe

possible

associationbetween indoorenviron¬

mental factors and asthma among

participants

of this

prevalence

surveyof

elementary

schoolchildren.

Materials and Methods

Study

Areas andSurveyProcedures

FourmunicipalitiesinKaohsiungwereselected for thepresent

study

basedontheurban-rural classificationinTaiwan.8Accord¬

ing to this classification, each municipality was given a 1 to 8

urbanizationcategory7. Municipalitieswith the

highest

urbaniza¬ tionlevel,suchastheTaipeimetropolitanarea,were

assigned

to

category 1,while

municipalities

withthelowest urbanization level

were

assigned

to category 8. The four

municipalities

selected

were

predominantly

rural and

they

were

assigned

tocategory8.

The rural areas selected forthepresent

study

also hadnolocal sources of industrialairpollution.9These areaswerejudgedto

(3)

the healthof childrenintheseareas was

unlikely

tobe influenced

by

regional

air

pollution.

Webelieve that the levels andtypesof

outdoorair

pollution

were

essentially

similarinthestudiedareas. All16

public

primaryschools within the

study

areas

agreed

to

participate in the

study.

A random

sample

ofone halfofthe

primary schools was chosen. All school

buildings

are made of

concreteandthe conditions inside the classroomsarealmostthe same.with no

particular

indoor air

pollution

sources for the

studied schools. All children from the first

through

the sixth

grades

(children6to 12yearsof

age)

inthe

eight

schoolswere

enrolledinthis

study.

Sample

sizes inparticipatingschools varied from350to700

pupils.

Aquestionnairethatevaluatedrespiratoryillnesses and symp¬

tomsofchildrenwas distributed tothechildren inthepartici¬

patingschools

by

theirteachers

during

the

period

fromSeptem¬

bertoNovember, 1994. Thequestionnairewas

completed

by

a

parent or

guardian

most familiar with the child's health and

returnedtotheschool.Thequestionswereobtainedormodified from other

previously

usedquestionnaires,

namely,

theAmerican

ThoracicSociety-DivisionofLungDiseaseRespiratorySymptom

Questionnaire,10 which was used in the Harvard Six Cities

Study,11

andthe questionnaireused

by

the Health andWelfare

DepartmentinCanadafora

community-based

study

of children's

health.12

Fromthe questionnaire, the

following

factorswere assessed:

environmental exposures in the homes of a chemical nature,

including

presence ofahouseholdsmokerinthehome;exposure to gas

cooking appliances;

mosquito

repellant burning;

and

incense

burning.

Otherenvironmentalfactorsofa

physical

nature

such aswhetherthe housecontained anaircleaner,

dehumidi-fier,orairconditioner,and other

biologic

factors

including family

ownership

of

furry

pets, carpeting,

plants

inside thehome, and home

dampness

werealsoassessed.Home

dampness

wasdefined

aspresence ofanyoneof the

following:

visiblemold ormildew

growth

onthe surfaces inside thehome, appearance of

standing

waterwithin the home;water

damage;

orwaterleaks into the

building.

Study Subjects

The

subjects

for the presentcase-control

study

wereselected fromtheparticipantsofthe

prevalence study.

Thequestionused

forcasedefinitionwas"Hasthe childeverhad asthma

diagnosed

by

adoctor?" Thecontrol

subjects,

selectedfromthesameschool and class and matchedonageand

gender,

didnothaveaprevious

diagnosis

ofasthma,

history

of

physician-confirmed

atopic dis¬ eases,persistent

wheezing, cough,

or

phlegm,

or

reported

chest

illness,pneumonia, orbronchitis.

Itwasestimatedthat,ifthetrueoddsratio(OR)was2,inorder

to detect an association betweenindoor environmental factors

and asthma witha

specificity

of95% (a=0.05) and apower of 80% (B=0.2),a

sample

sizeof75casesandan

equal

numberof controlsubjectswouldbeneeded.13

Statistics

Allstatistical

analyses

were

performed

usingstatistical software

(Statistical

Analysis

System; SAS; Cary, NC). A conditional

logistic

regression model was used to calculate OR and 95% confidence intervals (CIs)

adjusted

for other risk factors and for

potential confounding

factors.14 All statistical tests were two

sided.

Covariables used to adjust the associations between indoor environmental factors and asthma included the

following:

age,

gender,

highest

level of education achievedbyeitherparent,the child's

allergies,

eg,tofood, dust,orpollen,

parental

asthma,and

breast

feeding.

Results

The

parents

of all 4,389 children enrolled in the

eight

schoolsstudied receiveda

questionnaire;

4,213

(96%)

questionnaires

were returned.

Complete

in¬

formationwas availableon

4,164

children. Theprev¬

alence of asthma was 4%

(n=165)

and an

equal

number of matched control

subjects

wereidentified.

The

prevalence

is less than that

reported

by

a

study

conducted in

Taipei.4

This

study,

however,

usedadifferentcasedefinition

(they

definedcases as "achild who had hadat least three

recurrent,

paroxysmal

attacks of

wheezing

and

dys¬

pneain the

past

12

months")

andwas conductedin

an urban area.

Table 1shows the distribution ofcasesand control

subjects by

selected

personal

characteristics. There

were morecasesthancontrol

subjects

with

allergies,

a

family

history

of asthma

(parental

asthma),

and

higher

paternal

education. Control mothers breast

fed their child more often than case mothers did.

Having

a

history

of

pneumonia

or

tonsillectomy

was

not

reported by

any ofthe cases or control

subjects

(not

shown in Table

1).

Table 2 shows the indoor environmental charac¬ teristicsofthe

study subjects.

Therewere nonotable

differences between the cases and control

subjects

with

regards

tohousehold

smoking,

useof

dehumid-ifiers,

useofanair

cleaner,

useofanair

conditioner,

owning

furry

pets,

useof

carpets,

mosquito

repellent

burning,

and

having plants

inside the home. Home

dampness

had a

positive

and

statistically significant

associationwith asthma.

However,

a

negative

associ¬

ation was observed between asthma and incense

burning

and

frequency

ofgas

cooking.

AsshowninTable

3,

asthmawas

only

significantly

associated with home

dampness

(OR=2.65,

95%

01=1.52,

4.62)

when conditional

multiple

logistic

regression

was used to obtain estimates of

associa-Table 1.Characteristics

of

the

Study Population

Cases, % ControlSubjects,

(n=165) (n=165)

Age,yr,mean±SD

Malegender

Parental education^highschool Father* Mother Householdcrowding (people/room) >1 <1 Parentalasthma*

Allergy(food,dust,pollen)(any)"*

Breastfeeding* 10.68±2.86 53.3 63.6 43.6 88.5 11.5 7.9 35.8 38.2 10.61±2.74 53.3 50.3 41.2 90.3 9.7 0.6 8.5 44.8 *p<0.05. 394 ClinicalInvestigations

(4)

Table 2.Crude ORand95% CI

of

Indoor EnvironmentalFactors and Asthma

Factors

Cases, Control

No. Subjects,No. OR(95% CI) Householdsmoking None Any Useofadehumidifier No Yes

Useofanaircleaner

No Yes

Useofanairconditioner

No Yes Furrypets No Yes Carpets No Yes

Mosquitorepellent burning No

Yes

Incenseburning* No

Yes

Plantsinside the home

No Yes Gascooking* <l/d >l/d Homedampness* No Yes 75 90 140 25 157 31 134 120 45 144 21 79 72 93 89 76 21 144 44 121 67 98 136 29 158 38 127 105 60 144 21 103 62 41 124 99 66 10 155 85 80 1.00 0.83(0.54-1.27) 1.00 0.83(0.46-1.51) 1.00 1.16(0.39-3.47) 1.00 1.32(0.76-2.29) 1.00 0.67(0.43-1.06) 1.00 1.00(0.52-1.92) 1.00 1.51(0.98-2.35) 1.00 0.42(0.25-0.68) 1.00 1.28(0.83-1.93) 1.00 0.48(0.24-0.96) 1.00 2.95(1.80-4.84) *p<0.05.

tions

adjusted

for other risk factors. ORs were

adjusted

for age, sex,

parental

education,

parental

asthma,

physician-confirmed allergy

to food or

dust,

etc, and breast

feeding.

After

adjustment

for these

factors,

gas

cooking

and incense

burning

were not

significantly

associated with asthma.

Discussion

The

present

case-control

study

indicated that re¬

ported

home

dampness

wasthe

only

indoorenviron¬

mental factor that is associated with asthma for

children

residing

in

Kaohsiung

rural areas. This

finding

is in

agreement

with the

findings

of other

epidemiologic

studies.1523

Determinationofthe presenceof home

dampness

in this

study

relies on

self-reporting

and therefore was

subjective.

If

dampness

is

widely

held to be a cause of

asthma,

an association based

entirely

on

self-reported

information should be considered proneto

reporting

bias. This could be

possible

ifthe

parents

ofasthmaticchildren

report

dampness

inthe

home more

readily

than those whose children are

not asthmatic. This seems

unlikely,

however,

be¬ cause the

potential

role of

dampness

in thehome as arisk factor for asthma hasnotreceived much

public

attention in Taiwan.

Since determination of the presence of home

dampness

was based

entirely

on

self-reporting,

this

could result in misclassification of exposure and reduce the observed associations. However, several studies have

reported

the

validity

of

self-reported

housing

conditions and

independent

objective

as¬

sessments of

temperature,

humidity,

and mold

growth.19'20'24-26

In

addition,

the

questionnaire

did

notfocus

exclusively

on

dampness

inthe home. The

questions

related to

dampness

in the home and

growth

of molds were

widely separated

inthe ques¬

tionnaire and the

respondents generally

did not

know that

dampness

in the home and molds could

cause adverse health effects.

Therefore,

itwould be

reasonable to believe that it is

unlikely

that

overre-porting

or

underreporting

of

damp housing

condi¬

tions could have biased the

study

results.

Though

differences in

questionnaire

design,

lan¬ guage,

climate,

and

housing

conditions mayexist,the

ORs found inthe

present

study

are similar to those

reported

from other countries.1517'2022 The consis¬

tency

of our results with those of

epidemiologic

asso¬

ciationto beconsidered causal.

Therefore,

the asso¬

ciations between asthma and

dampness

inthe home

are

probably

causal,

although

doubtremainsbecause

ofthe

subjective

nature of the

self-reporting.

Fungi,

house dust mites, and cockroaches are

known tobe more

prevalent

in

damp

homes than in

dry

homes,

and allare knownto

produce

substances

that may

trigger

allergic

reactions.27-35Taiwanis in a

subtropical

climate,

and

high

relative

humidity

(>80%)

occurs

throughout

the year. House dust

mites and

fungi

are the

major

allergens

in our

subtropical

area.36

Aspergillus,

Penicillium,

and

Cla-dosporium

are the

predominant

genera, and their

Table

3.Adjusted

ORs (95% CIs)

for

theAssociation RetweenIndoor EnvironmentalFactorsand Asthma*

Variable CrudeOR _Adjusted_OR_(95%_CI)

Gascooking Incenseburning Home dampnessf 0.48 0.42 2.95 1.16(0.50-2.68) 1.53(0.90-2.58) 2.65(1.52-4.62)

*Adjustedfor age, sex, parentaleducation, parentalasthma, physi¬

cian-confirmedallergytofood, dust,orpollen, andbreastfeeding.

(5)

indoor levels are

higher

than levelsin other

parts

of

the world.3738 A

study

has demonstrated the

validity

of

questions

in

regard

to

dampness

and

molds as indicators of indoor mold

growth,

and the

respondent's

perception

of home

dampness

hasbeen correlated with measured spore levels.20 In the

present

study,

however,

the concentrationsof

fungi,

house dust mites, and cockroaches were not deter¬

mined.

Therefore,

there is no direct evidence to

show that this mechanism is

responsible

for the

observed associations between

dampness

of the home and asthma.

The indoor environmental factors that have re¬

ceived the most attention in the

past

are environ¬

mental tobacco smoke and

directly

or

indirectly

measured

nitrogen dioxide,

which

mainly

comes

from gas

cooking appliances. Although

manystudies have shown a

statistically significant relationship

between

passive

smoking

and childhood asth¬

ma,111839-45

our

study

did not. This inconsistent

finding

maybe due

partly

tothe fact thatwedidnot assess whether household smokers

actually

smoked

indoorsor

because,

in

developing

countries, manyof

those who smoke

actually

smoke

only

a few

ciga¬

rettes per

day.

Also we did not determine which

parent

smoked. This could be

important

since ma¬

ternal

smoking

indoorsmaybea

greater

riskfactorto

children.

Furthermore,

almost all the students in rural Taiwan walk to school. We think that the

probability

that the effects of

parental

smoking

inside the car with the children

present

may have

affected ourresults is

negligible.

We didnot findanassociation between gas cook¬

ing

andasthma. Thisresultis consistentwith several

other

reports

that also found that the use of gas

cooking appliances

was not

significantly

associated

with asthma.1141-44'46In

reality,

itwasnot

possible

to

see any

impact

of gasstove use on

respiratory

health

because

nearly

91% of the homes of the

study

subjects

(87.3%

of thecasesand93.9%ofthecontrol

subjects)

used gas stoves for food

preparation

more

than onetime per

day.

The

burning

of Chinese incense for

worshipping

deities is a

daily

routine for most Chinese. The

smoke

produced by

this

practice

has been found to

contain

formaldehyde.47

Exposure

toindoor formal¬

dehyde

may cause asthma48 or asthma-like symp¬

toms.49 Incense

burning

was not shown to be a

significant

risk factorinthis

study (adjusted

OR,

1.53

[CI,

0.90 to

2.58]).

Burning

mosquito

repellents

isa common sourceof indoorair

pollution

in

subtropical

rural areas. In this

study,

the

prevalences

of mos¬

quito

repellent burning

were 47.9% and 37.6% for

thecases and the control

subjects,

respectively.

The

potential

harmfulness of

products produced

by

burn¬

ing mosquito

repellent

has been

acknowledged.50

Two studies conducted in

tropical

countries have

found that exposure to

mosquito

repellent

smoke

wasassociated withasthma.5152Inthis

study,

wedid

notfind anassociationbetweeneitherincenseburn¬

ing

smoke or

mosquito

repellent

smoke exposure

andasthma.

However,

their

potential

forharm mer¬

its further

study

in

subtropical

areas.

In

conclusion,

in this

study,

we

investigated

the

relationship

between several indoor environmental factors and childhood asthma. Of the many indoor

environmental factors included in this

study,

only

home

dampness

was found to be associated with

asthma. This

finding

supports

the

hypothesis

ofan

associationbetween asthma and

reported

dampness

in the

home,

which has been observed in other

recent

epidemiologic

studies. In view of the

high

relative

humidity

in

subtropical

areasand the results

of the

present

study,

home

dampness

shouldbecome

a new

public

health issue for Taiwan's

population.

The

possible

adversehealth effects of

damp

housing

deservefurther

study.

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(7)

DOI 10.1378/chest.114.2.393 1998;114; 393-397

Chest

Chun-Yuh Yang, Meng-Chiao Lin and Kuang-Chi Hwang

Childhood Asthma and the Indoor Environment in a Subtropical Area

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