J. Paediatr. Child Health (1998) 34, 47–52

Prevalence and risk factors of childhood asthma,rhinitis and eczema in Hong Kong

YL LAU and J KARLBERG

Department of Paediatrics, University of Hong Kong, Queen Mary Hospital, Hong Kong

Objective: To assess the prevalence and risk factors of childhood asthma and allergies in Hong Kong and comparewith that in Singapore and Great Britain.Methodology: Parents of 3618 randomly selected 6- to 7-year-old children responded to a questionnaire preparedby the International Study of Asthma and Allergies in Childhood (ISAAC) together with supplementary questions on riskfactors.Results: The 12-month prevalences of wheezing, rhinitis symptoms and itchy rash were 9.2%, 35.1% and 4.2%, respectively.Wheezing in the past year was significantly associated with rhinitis symptoms in the past year, itchy rash in the past year,rhinitis interfering with daily activities moderately or severely, kept awake by itchy rash in the past year, parental wheezing(one or both parents), frequent upper respiratory tract infections (URTI), born in Hong Kong and male sex. For girls, theprevalence of wheezing in the past year was lowest when they were born in July/August and highest when born in January/February.Conclusions: The prevalence of allergic disorders in Hong Kong was comparable to that in Singapore and Great Britain.Several potential risk factors such as parental wheezing, frequent URTI, born in Hong Kong, male sex and month of birth ingirls were identified.

Key words: asthma; children; eczema; prevalence; rhinitis; risk factors.

The epidemiology of childhood asthma and allergies is of MATERIALS AND METHODSconsiderable interest and importance because of the increasingeconomic impact on the health services1,2 and a possible Questionnairesincrease in its prevalence and severity, both in Western3,4 and

The ISAAC questionnaires for asthma, rhinitis and eczema weresome Asian countries.5,6 Factors responsible for causing asthmaidentical to those used previously,8,10,11 and the questionnairesor precipitating attacks are still poorly defined and changes inwere translated into Chinese for local use. For question 1 onlife style and environment that are associated with urbanisationwheezing, several translated terms were used, including aand development may be partly responsible for the increase indescription of breathing sound of ‘HEHE’, in order to facilitateboth prevalence and severity.7 With the rapid economicrecognition of the symptom of wheezing. Because of the raritydevelopment in Asia in the past decade, the prevalence ofof hayfever in Hong Kong, a question was added regardingasthma has also increased from a relatively low level to one‘allergic rhinitis’. Some extra questions on potential factorsthat the health care planners cannot ignore.8,9

associated with wheezing were also added. The translatedAlthough many epidemiological studies have been andquestionnaire has not yet been validated.continue to be undertaken, there are methodological differences

which hinder valid comparison between countries and overtime. It is therefore important that epidemiological surveys on

Data collectionasthma and allergies be standardised; to this end theInternational Study of Asthma and Allergies in Childhood (ISAAC)

Each school in Hong Kong with students aged 6–7 years oldwas established in 1992.10

was given a number and a random list was generated. SchoolsThis paper reports the results of a study using the ISAACwere approached in the order of the random list and werewritten questionnaire in a survey of 6- to 7-year-old Hong Kongrecruited to participate if consent from schools was obtained.children in 1995. The results are compared with two publishedThe first 17 schools that consented provided an adequatestudies using the same ISAAC protocol in 6- to 7-year-olds,number of 6–7 years old children to undertake the study. Theone in Great Britain11 and one in Singapore.8parents were the respondents and the survey was carried outbetween April and May 1995.

Climatological correlation

Correspondence: YL Lau, Department of Paediatrics, The University ofMonthly mean temperature, humidity and rainfall from 1961 toHong Kong, Queen Mary Hospital, Pokfulam Road, Hong Kong.1990 were correlated with the monthly prevalence of rhinitisYL Lau, MD, FRCP. J Karlberg, MD, PhD.

Accepted for publication 4 August 1997 symptoms.12

YL Lau and J Karlberg48

Data analysis In a stepwise logistic regression analysis, four factors werefound to be significantly associated with wheezing in past year:(i) parental wheezing (one or both parents, OR=4.5, 95% CI=Statistical analysis includes percentages, odds ratio, 95%3.33–6.10); (ii) frequent upper respiratory tract infection (URTI;confidence interval, chi-square test and multiple regressionnumber ≥4 per year, 95% OR=3.0, CI=2.35–3.83); (iii) bornanalysis. The Mantel–Haenszel stratified analysis was used toin Hong Kong (OR=2.3, 95% CI=1.35–3.80); (iv) male sexcontrol the basis of the procedure of sampling of the schools.(OR=1.5, 95% CI=1.14–1.87). The prevalence of wheezing inOnly two tailed tests were used. All data were analysed usingthe past year was 27.2% (95% CI=22.2–32.1%) when parentalSAS/PC.13

wheezing was present, 16.7% (95% CI=11.8–21.6%) when thechild had frequent URTI, 9.8% (95%CI=8.8–10.8%) when thechild was born in Hong Kong and 10.3% (95%CI=8.9–11.7%)RESULTSfor boys. In contrast, the prevalence of wheezing in the pastyear was 7.3% (95%CI=6.4–8.2%) when parental wheezingThere were 3618 questionnaires returned, representing awas absent, 6.8% (95%CI=5.8–7.7%) when the child had lessresponse rate of 97%. Approximately 49% of the children (n=frequent URTI, 4.6% (95%CI=2.8–6.5%) when the child was1776) were female and all but 24 (0.7%) were Chinese. Schoolborn outside of Hong Kong and 8.1% (95%CI=6.8–9.4%) forchildren from the three regions of Hong Kong, i.e. Hong Konggirls. For maternal wheezing alone versus no maternal wheezing,Island, Kowloon and New Territories, were proportionallythe odds ratio is 6.39 (95% CI=4.63–8.82, P<0.0001, 36.3%represented by the sample population. Approximately 18% ofvs 8.0%); for paternal wheezing alone versus no paternalthe sample children were from Hong Kong Island, 36% fromwheezing, the OR is 3.89 (95% CI=2.75–5.50, P<0.0001,Kowloon and 46% from New Territories; the respective figures26.8% vs 8.3%); for both parents being wheezy versus nofor the total primary school children were 19%, 33% and 48%.parental wheezing, the OR is 14.48 (95% CI 8.24–25.47,There were varying numbers of missing data for each of theP<0.0001, 54.3% vs 8.6%).

questions and these are evident from the responses as shownFor those who were not born in Hong Kong, it was found

in the tables. The prevalence and severity of asthma symptomsthat those who came to Hong Kong before 27 months of age

for the whole group and the odds ratio of male as compared had a prevalence of 6.1% (9/147) of wheeze in the past yearto female of having that symptom are shown in Table 1. compared to that of 3.2% (7/220) if they came to Hong Kong

Similarly the prevalence and severity of rhinitis symptoms after 27 months of age (OR=2.0, 95% CI=0.73–5.4, P = 0.18).are shown in Table 2, and those of eczema in Table 3. The In a logistic regression analysis of non-Hong Kong born children,monthly variation of rhinitis symptoms and the corresponding the OR of wheeze in the past year was 5.9 (95% CI=1.14–30.2)meterological parameters are shown in Fig. 1. After multiple for maternal wheezing (P=0.04), 4.8 (95% CI=0.94–24.4) forregression analysis using logarithmic percentage prevalence paternal wheezing (P=0.06) and 1.7 (95% CI=0.55–4.96) ifvalues as the dependent variable, only sex and rainfall were they came to Hong Kong before 27 months of age (P=0.37).shown to be significant factors affecting monthly prevalence of The sex and month of birth did not show significant associationrhinitis symptoms (P=0.0001), but not temperature or humidity with wheeze in this group. However, in analysing the effect of(P>0.05). The monthly rainfall was negatively correlated with month of birth on prevalence of wheezing in the past year forthe monthly prevalence of rhinitis symptoms for boys and girls the whole group, it was found that in girls there was a significant(r2=0.98, P<0.0001)(Fig. 2). association, with lowest prevalence (4.1%, 95% CI=1.8–6.5%)

The association of wheezing in the past year with rhinitis and when they were born in July/August and highest (11.5%, 95%eczema is shown in Table 4. Regarding birthplace, there were CI=7.3% to 15.6%) when they were born in January/367 children born outside and who subsequently emigrated to February (Fig. 3).Hong Kong in the present study. There were data on 302 ofthese 367 children regarding where they were born. Most (227,75.2%) were born in China and 193 of these 227 (86%) were DISCUSSIONborn in the southern coastal provinces of Guangdong andFujian, from where most Chinese people in Hong Kong Limited population-based studies on childhood asthma in Hong

Kong are available for comparison.14–16 The prevalence oforiginated. About 20% (n=61) were born outside Asia.

Table 1 Prevalence and severity of asthma symptoms

Boys Girls TotalQuestion % % % OR 95%-CI P-value

1. Wheeze ever Yes 18.9 14.5 16.8 1.42 1.19–1.71 0.00012. Wheeze in past year Yes 10.3 8.1 9.2 1.32 1.04–1.66 0.033. Wheezing episodes in past year ≥4 2.8 1.7 2.3 1.77 1.11–2.83 0.024. Woken by wheeze in past year >0 3.8 2.1 2.9 2.71 1.19–6.15 0.0035. Limitation of speech during wheeze Yes 1.2 0.4 0.8 2.71 1.19–6.15 0.02in past year6. Asthma ever Yes 10.0 5.5 7.8 1.95 1.51–2.53 <0.00017. Exercise-induced wheeze in past Yes 8.3 5.7 7.1 1.52 1.17–1.99 0.002year8. Nocturnal cough in past year Yes 22.9 21.2 22.1 1.10 0.94–1.30 0.24

OR, odds ratio of male to have that symptom compared to female.

Asthma, rhinitis and eczema in Hong Kong 49

Table 2 Prevalence and severity of rhinitis symptoms

Boys Girls TotalQuestion % % % OR 95%-CI P-value

1. Rhinitis ever Yes 42.2 35.4 38.9 1.32 1.15–1.52 0.00012. Rhinitis in past year Yes 38.8 31.3 35.1 1.40 1.21–1.62 0.00013. Itchy eyes in past year Yes 17.1 13.7 15.4 1.33 1.10–1.62 0.0044. Rhinitis occurred in Jan Yes 15.1 11.2 13.2 1.41 1.16–1.71 0.0011

Feb Yes 16.6 13.8 15.3 1.24 1.03–1.49 0.02Mar Yes 15.5 12.5 14.0 1.28 1.06–1.55 0.009Apr Yes 9.7 6.6 8.2 1.52 1.19–1.93 0.001May Yes 5.7 3.8 4.7 1.53 1.12–2.09 0.008Jun Yes 4.2 3.2 3.7 1.34 0.94–1.89 0.10Jul Yes 4.7 3.5 4.1 1.37 0.99–1.91 0.06Aug Yes 4.7 3.5 4.1 1.37 0.99–1.91 0.06Sept Yes 6.3 4.6 5.4 1.40 1.04–1.87 0.03Oct Yes 11.0 7.2 9.2 1.60 1.27–2.01 0.0001Nov Yes 14.5 10.5 12.5 1.45 1.19–1.77 0.0002Dec Yes 16.6 12.7 14.7 1.38 1.14–1.66 0.0008

5. Rhinitis interfering with daily M–S 2.5 1.7 2.1 1.36 0.84–2.20 0.22activities6. Hayfever ever Yes 1.2 1.2 1.2 0.85 0.45–1.61 0.627. Allergic rhinitis ever Yes 35.8 27.9 31.9 1.48 1.27–1.71 <0.0001

OR, odds ratio of male to have that symptom compared to female.M–S, interfering with daily activities moderately or severely compared to not at all or a little.

Table 3 Prevalence and severity of eczema symptoms

Sex of childBoys Girls Total

Question % % % OR 95%-CI P-value

1. Chronic rash ever Yes 5.2 6.3 5.7 0.86 0.64–1.15 0.312. Chronic rash in past year Yes 3.6 4.9 4.2 0.75 0.54–1.06 0.103. Typical areas of chronic rash Yes 3.7 4.8 4.2 0.81 0.58–1.14 0.244. Rash, first occurred <2 24.4 29.2 27.0 1.16 0.54–2.47 0.715. Rash, all cleared in past year Yes 36.1 28.1 31.8 1.44 0.70–2.95 0.336. Kept awake by rash in past year >0 1.4 1.8 1.6 0.74 0.44–1.26 0.277. Eczema ever Yes 28.8 27.2 28.1 1.09 0.93–1.27 0.26

OR, odds ratio of male to have that symptom compared to female.

wheeze ever was 9% in 1989,14 8.6% in 199216 and 16.8% in children,8,11 which used identical survey methodology to thepresent study. The prevalences of wheeze ever and wheeze inthe present study in 1995. Our previous study in 1989 gave a

prevalence of doctor-diagnosed asthma of 6.0%,15 which was the past year were similar in both Great Britain (24.4% and16.7%, respectively) and Singapore (28.6% and 16.5%, respect-similar to that of 6.7% in another study in 1989,14 while the

prevalence of doctor-diagnosed asthma in the present study ively). The corresponding figures for Hong Kong were lower at16.8% and 9.2%, respectively. The discrepancy of 5% to 10%was 7.8%. There are, however, many confounding factors which

may explain the apparent increase, such as differences in between the prevalence of wheeze ever and that of wheeze inthe past year probably reflects the proportion of wheezy infantssurvey methodology and possible increase in awareness of

wheezing illnesses and asthma among the general public. This who would stop wheezing by the age of 6 years, which hasbeen documented in a longitudinal study of wheezing illnessesapparent increase was also reflected in both allergic rhinitis

and eczema, the prevalence of which was 16.3% and 6.8% in in Tucson, U.S.A.17

The prevalence of rhinitis symptoms ever and rhinitis198914,15 and 31.9% and 28.1% in this survey in 1995. Directcomparison may not be valid but the increasing trend is in symptoms in the past year were similar for both Hong Kong

(38.9% and 35.1%, respectively) and Singapore (30.8% andaccordance with that in the Western countries3,4 and inSingapore,8 a city-state which is similar to Hong Kong in terms 27.6%, respectively). The prevalence of itchy rash ever and

itchy rash in the past year were higher in Singapore (10.5%of the rapid pace of urbanization and westernization of life-style. In Singapore, the reported wheeze ever increased from and 8.8%, respectively) than in Hong Kong (5.7% and 4.2%,

respectively). Despite using identical ISAAC methodology, direct5.5% in 1967 to 20.0% in 1994.8 The increase in the prevalenceof asthma symptoms may be due to increased awareness or comparison may still be invalid because of differences in

cultural and linguistic backgrounds; for example, in therepresent a true increase, the reasons for which are complexbut may include increased exposure to allergens such as house Singapore study of predominantly Chinese children (85%), the

questionnaire was administered in English and a high proportiondust mites.3There are two published ISAAC studies of 6- to 7-year-old of Chinese respondents (53.4%) stated they did not understand

YL Lau and J Karlberg50

Fig. 1 Monthly variation of prevalence of rhinitis symptoms and the monthly Fig. 2 Correlation of monthly rainfall with the monthly variation of prevalenceclimatic factors; boys (circles) and girls (triangles). of rhinitis symptoms given in logarithmic values; boys (circles) and girls

(triangles); r2=0.98, P<0.0001.

the diagnostic label of eczema. This lack of understanding ofeczema perhaps resulted in a low positive rate of 3.0% in the winter months because most houses do not have central

heating and people do not keep the windows tightly closed.Singapore study. In contrast, the questionnaire in the presentstudy was in Chinese and the prevalence of eczema ever was However, other confounding factors such as viral URTI could

also be involved. Of 985 children reported to have rhinitis28.1%. The reported prevalence of eczema has increased from6.8% in 198915 to 19.1% in 1992,16 to 28.1% in 1995. This symptoms in certain months, 100 had rhinitis symptoms

throughout the year and about 800 had no symptoms fromemphasises the importance of validating even a standardquestionnaire, whether translated into another language or not, June to August.

Boys were more affected than girls in terms of prevalencein each population being studied. Such validation of the ISAACquestionnaire in the Chinese population is being planned in and severity for both wheezing and rhinitis symptoms (Tables 1

and 2). Ten percent of boys were reported to have asthma asHong Kong.The reported prevalence of hay fever in the present study compared to 5.5% of girls (OR=1.9); 35.8% of boys and 27.9%

of girls had allergic rhinitis (OR=1.44). Such male predominancewas extremely low at 1.2%, even lower than that of 4.4% forthe Singapore Chinese children,8 despite an extremely high was observed in the other two ISAAC studies in Singapore8 and

Great Britain.11 However, for eczema symptoms there was noprevalence of rhinitis symptoms of 38.9%. This suggests eitherlack of understanding of the diagnostic label of hay fever or male predominance and there might even be a slightly higher

female rate of itchy rash in past 12 months, with 4.9% for girlsthat the rhinitis symptoms were caused by perennial rhinitis. Inthe Singapore study, 52.8% of the Chinese respondents were and 3.6% for boys (Table 3). In the Singapore study, females

tended to have more severe eczema.8 Male sex therefore seemsnot aware of the diagnostic label of hay fever and there was noseasonal variation in their reported rhinitis symptoms, perhaps to predispose to respiratory mucosal allergy but not cutaneous

allergy; the immunological basis for this is still unclear, althoughrelated to the relatively constant climate. However, in thepresent study there was a significant seasonal variation, with a difference in immunity between males and females has been

documented, for example in the levels of serum IgM.19higher rate of reported rhinitis symptoms from October to April.The higher rate of rhinitis symptoms during the autumn and Only 7.8% of the children in the present study had been

given previously the diagnostic label of asthma, which waswinter months was related to the lower rainfall, which mayencourage the dispersal of aeroallergens such as fungal spores, much lower than that of 16.8% with wheeze in the past but

only slightly lower than that of 9.2% with wheeze in the pastdust and house dust mites.18 In Hong Kong the indoor homeenvironment would be much the same as that of the outdoor 12 months (Table 1). This suggests a degree of underdiagnosis

of asthma; however, in a study validating a questionnaire onenvironment in terms of temperature and humidity during the

Asthma, rhinitis and eczema in Hong Kong 51

Table 4 Association of wheeze in last year with rhinitis and eczema symptoms

Wheeze in past yearYes No Total

Question % % % OR 95%-CI P-value

1. Rhinitis ever Yes 76.4 34.4 38.4 6.06 4.72–7.77 <0.00012. Rhinitis in past year Yes 75.1 30.6 34.8 6.70 5.24–8.56 <0.00013. Itchy eyes in past year Yes 46.4 12.1 15.4 6.04 4.81–7.59 <0.00014. Rhinitis interfering with daily activities M–S 7.4 1.53 2.1 5.17 3.25–8.25 <0.00015. Chronic rash ever Yes 13.6 5.0 5.8 2.91 2.05–4.12 <0.00016. Chronic rash in past year Yes 11.4 3.6 4.3 3.29 2.25–4.79 <0.00017. Kept awake by rash in past year >0 5.5 1.3 1.6 4.42 2.57–7.62 <0.0001

OR, odds ratio of having that symptom if wheezing in past year was present compared to no wheezing in past year.M–S, moderately or severely.

Girls

Months of birth Months of birth

Boys

Fig. 3 The effect of month of birth of boys and girls on the prevalence and its 95% confidence intervals of wheeze in past 12 months.

bronchial symptoms in predicting bronchial hyperreactivity, the infections during infancy may enhance airway hyperresponsive-ness;22 however, viral infections also have been suggested toquestion on ‘wheeze in last 12 months’ was shown to be the

most sensitive but the least specific, while ‘asthma in last 12 be protective against asthma.23 This association may also justbe an effect of recall, i.e. parents of children whose URTImonths’ was the least sensitive but the most specific.20 In

contrast, the percentages of children with rhinitis symptoms in triggered an episode of wheeze would be more likely to recallthe URTI than parents whose children had no wheeze.the past (38.9%) and allergic rhinitis in the past (31.9%) were

quite similar (Table 2), suggesting a reasonable level of It was interesting to note that those who were born in HongKong had a higher risk of wheezing than those who were notawareness of the diagnostic label of allergic rhinitis among the

general public in Hong Kong. born in Hong Kong (mainly born in mainland China). Leung andHo also found significantly lower prevalence of asthma inWheezing in the past 12 months, as expected, was signifi-

cantly associated with rhinitis symptoms and itchy rash in the Chinese children living in mainland China than in children ofsimilar origin living in Hong Kong.24 This difference in thepast 12 months (Table 4), supporting the concept of an atopic

predisposition. Moreover, wheezing in the past 12 months also wheezing prevalence may be caused by different early lifeexperiences of these two groups. The influence of early liferesulted in increased severity of rhinitis and eczema (Table 4).

The genetic predisposition to wheezing was reflected by its experiences is further supported by our observation that thoseout-born children who migrated to Hong Kong before 27 monthsassociation with parental wheezing (OR=4.5), especially with

maternal wheezing. The reason for the association of increased of age had an odds ratio of 2.0 of having wheeze in the past12 months compared to those who migrated after 27 monthsfrequency of URTI with wheezing was not clear. The same

association was documented in our previous study.15 Up to of age. The choice of using 27 months old as cut-off was toobtain approximately an equal sample size in both groups for80–85% of asthma exacerbations in school-age children were

associated with or triggered by viral URTI.21 Repeated viral comparison, but the difference did not reach statistical

YL Lau and J Karlberg52

9 Hsieh KH, Shen JJ. Prevalence of childhood asthma in Taipei,significance, probably because of the small sample size. TheseTaiwan and other Asian Pacific countries. J. Asthma 1988; 25: 73–82.experiences could even be operating during the fetal stage and

10 Asher MI, Keil U, Anderson HR, et al. International study of asthmamay include exposure to dietary and aeroallergens. In a nationaland allergies in childhood (ISAAC): rationale and methods. Eur.study of 900 000 children aged 9–14 years in China betweenRespir. J. 1995; 8: 483–91.

1988 and 1990, the prevalence of asthma was lowest in Tibet 11 Strachan DP, Anderson HR, Limb ES, O’Neill A, Wells N. A national(0.11%) and highest in Fujian (2.03%).25 Tibet is at high altitude, survery of asthma prevalence, severity, and treatment in Greatwhile Fujian is by the coast. Hong Kong is situated at the Britain. Arch. Dis. Child. 1994; 70: 174–8.southern coast of Guangdong, which is the most southern 12 Myers H. Hong Kong 1995. Government Printer, Hong Kong

1995; 525.province in China. The early life experiences hypothesis was13 SAS/PC. SAS Institute Inc., Cary, NC, 1992.further supported by the findings that the month of birth could14 Ong SC, Liu J, Wong CM, et al. Studies on the respiratory healthbe associated with allergic diseases.26–28 In the present study

of primary school children in urban communities of Hong Kong.this association was only significant in girls for the whole groupSci. Total Environ. 1991; 106: 121–35.but was not seen in children born outside of Hong Kong. Being

15 Lau YL, Karlberg J, Yeung CY. Prevalence of and factors associatedborn in the wet season seemed to confer protection against with childhood asthma in Hong Kong. Acta Paediatr. 1995;wheezing for girls in Hong Kong but the reason is still unclear. 84: 820–2.

In conclusion, the prevalence of atopic disorders in Hong 16 Leung R, Tseng R. Allergic diseases in Hong Kong schoolchildren.Kong was comparable to that found in the U.K. Potential risk The Hong Kong Practitioner 1993; 15: 2409–20.

17 Martinez FD, Wright AZ, Taussig LM, Holberg CJ, Halonen M,factors were also identified, including parental wheezing, bornMorgan WJ. Asthma and wheezing in the first six years of life. N.in Hong Kong, month of birth in girls, male sex and increasedEngl. J. Med. 1995; 332: 133–8.number of URTIs.

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19 Lau YL, Jones B, Yeung CY. Biphasic rise of serum immunoglobulinsACKNOWLEDGEMENTS G and A and sex influence on serum immunoglobulin M in normal

Chinese children. J. Paediatr. Child Health 1992; 28: 240–3.We thank Mrs Christine Yan, research nurse, for data collection. 20 Burney PG, Chinn S, Brittion JR, Tattersfield AE, Papacosta AO.This project was supported by Health Services Research Fund What symptoms predict the bronchial response to histamine?

Evaluation in a community survey of the bronchial symptoms(No. 422007) and The University of Hong Kong.questionnaire (1984) of the International Union against Tuberculosisand Lung Disease. Int. J. Epidemiol. 1989; 18: 165–73.

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