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Socioeconomic Status And Indicators Of Asthma In Children

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SOCIOECONOMIC STATUS
AND INDICATORS OF ASTHMA
IN CHILDREN

 

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PIERRE ERNST, KITAW DEMISSIE, LAWRENCE JOPSEPH, ULI LOCHER, and MARGARET R. BECKLAKE

Respiratory Epidemiology Unit, Department of Epidemiology and Biostatistics, and Department of Sociology, McGill University, Montreal, Quebec, Canada.


ABSTRACT

 Differential access and utilization of medical care by the poor and rich may contribute to difference in asthma prevalence. We therefore studied the relationship of socioeconomic status (SES) to various indicators of asthma in the Canadian context of universal access to medical care. Information on respiratory symptoms, demographics, and home exposure of 1,111 primary school children was collected by questionnaire. Parental occupation was used to establish SES. Exercise-induced broncospasm (EIB) after a 6-min free-running test was our measure of airways responsiveness and was available for 989 children. As compared with children from the most advantaged homes, children from the least advantaged homes were more likely to present EIB (OR: 2.26, 95% CI: 1.12 to 4.58) and to report night cough (OR: 2.30, 85% CI: 1.04 to 5.06) and cough with mucus (OR: 3.15, 95% CI: 1.06 to 9.33), while there was no significant excess of the report of wheeze or diagnosed asthma. Among factors potentially linked to SES, the presence of a cat at home (OR: 1.63, 95% CI: 1.02 to 2.61) and lower respiratory infection before 2 yr of age were associated with an excess of EIB (OR: 1.71, 95% CI:1.16 to 2.52). Our results suggest that unidentified environmental factors contribute to the excess asthma morbidity in poor children.

 Ernst P, Demissie K, Joseph L, Locher U, Becklake MR. Socioeconomic status and indicators of asthma in children.

 AM J RESIR CRIT CARE MED 1995;152:570-5

 The results of studies examining the relationship of socioeconomic status (SES) to the prevalence of childhood asthma have been contradictory. Some studies have found a significantly higher prevalence of asthma in children of parents of lower social class (1-4), while other studies reported no association (5, 6) or a higher prevalence of asthma when parents came from more disadvantaged backgrounds (7, 8). The relationship of SES to respiratory symptoms has been more consistent, usually showing an excess of respiratory symptoms with lower SES (9, 10). Most of the population-based studies examining the relationship of SES to childhood asthma have used parental reporting to assess the respiratory outcomes. Differences in reporting behaviour among parents of different social classes may bias such associations.

 [...]

 The objectives of the present were (1) to examine the relationship of SES to childhood exercise- induced bronchospasm (EIB) in an area where there is universal access to medical care; (2) to investigate whether the association of SES to EIB or respiratory symptoms could be explained by environmental factors linked to SES, such as exposure to Environmental Tobacco Smoke exposure (ETS), heating and cooking fuel used in the home, presence of pets, asthma in a parent, daycare attendance, and reported history of lower respiratory infection (LRI) up to 2 yr. of age.

METHODS
 
 

  • Study population

  •  

     

Eighteen schools were selected on the island of Montreal in order to represent a broad range of SES. To achieve this, all schools in the five school boards in central Montreal were ranked according to neighbourhood average house values. Within each school board, schools were selected from the upper, middle, and lower ranges of neighbourhood average house value. One class from each school from each of grades One (5 to 7 yr of age), three (8 and 9 yr. of age), and five (10 to 13 yr. of age) was selected. A total of 1,274 children were recruited for the study. 

  • Respiratory Questionnaires

  •  

     

[...]

 The child's exposure to Environmental Tobacco Smoke both in utero (maternal smoking during pregnancy) and post-natally was also assessed, and an attempt was made to quantify current smoking exposure by inquiring about the number of smokers in the home and the average number of cigarettes smoked per day at home (household ETS). 

[...]
 
 

  • Lung Function

  •  

     

[...]
 
 

  • Assessment of Socioeconomic Status

  •  

     

Parental occupation was transformed into an SES score by coding the last occupation of the parents into the corresponding codes of the Canadian Classification and Dictionary of Occupations (17). These codes were then converted into SES scores (the highest score from either parent was retained for analysis) for the child based on income and education level for each occupation from the tables developed by Blishen and associates (18). The validity of questionnaire-reported work history is well-documented (19). 

  • Statistical Methods

  •  

     

[...]

 RESULTS
 
 

  • Characteristics of the Study Population

  •  

     

Of the 1,274 children, selected from 18 schools, the parents of 130 (10.2 %) refused participation for their children while a further 75 (5.9%) children did not return the questionnaire. There were no meaningful differences between participants and non-participants as to age of the child (mean [SD]: 8.8 [1.8] versus 8.0 [1.9]), gender (boys: 50.5 versus 55.4%), race (caucasians: 78 versus 89.9%), neighbourhood SES assessed by the Census data (poorest SES quartile: 26.6 versus 22%). Among families who refused permission for their child to participate in testing at school but did return the questionnaire (n = 99), mothers were less likely to be currently smoking (18.8 versus 37.9%) but no meaningful differences were seen in terms of respiratory symptoms, type of heating, cooking fuel used, and pets. Spirometry...

 [...]
 
 

  • Socioeconomic Status

  •  

     

Of the 989 children with satisfactory spirometric data, and SES score based on parental occupation was available for 916 (92.6%) children. Eighteen (1.8%) children had parents who were students. For 55 (5.6%) children, parents either did not report their occupation or reported an occupation that was uncodable. The distribution of selected socio-demographic variables by race is shown in Table 2. Non-Caucasian children were more likely to have come from disadvantaged families with low levels of parental education and with crowding, whereas Caucasian children were more likely to have come from homes with higher levels of ETS exposure and more likely to contain pets. Comparison of the age, level of effort attained (% maximum heart rate), and atmospheric conditions in those children with EIB and in those without EIB did not show important differences. 

  • Indicators of asthma and socio-economic status

  •  

     

[...]

 ... We investigated further if the observed relationship o SES to both EIB and respiratory symptoms could be explained by the following patterns: maternal smoking during pregnancy, household ETS, type of heating and cooking fuel used at home, current presence of a cat in the home, child daycare attendance, crowding, a history of LRI before 2 yr of age, and single-parent family status. The effect of low SES on EIB or respiratory symptoms persisted even after these variables were included in a model with SES, either one at the time or simultaneously (see odds ratios after complete adjustment in Table 3).
 
 

  • Further risk factors for exercise-induced broncospasm and other indicators of asthma

  •  

     

EIB was not found to be associated with either maternal smoking during pregnancy or current household ETS exposure (Table 4). 

TABLE 4   Unadjusted
o.r. (95% CI) Adjusted (*)
O.R. (95% CI) Household environmental tobacco smoke exposure (+)     None (0 cigarette/day) 1.00 (Reference) 1.00 (Reference) Light (< 10 cigarettes/day) 1.00 (0.62-1.59) 0.92 (0.53-1.58) Moderate (11 to 24 cigarettes/day) 0.73 (0.44-1.20) 0.66 (0.35-1.25) Heavy (> 25 cigarettes/day) 0.99 (0.65-1.51) 0.99 (0.57-1.73) Maternal smoking during pregnancy 0.81 (0.56-1.18) 0.86 (0.58-1.27) Cat currently in the home 1.56 (++) (1.04-2.34) 1.63(++) (1.02-2.61) Lower respiratory infection
before 2 yr. of age 1.51 (++) (1.07-2.15) 1.71(++) (1.16-2.52) Daycare attendance 1.04 (0.74-1.46) 1.01 (0.72-1.43)

(*) Adjusted for age, gender, race, socioeconomic status, asthma in a parent, and terms in the table
(+) Environmental tobacco smoke exposure, current, obtained by multiplying the number of smokers by the number of cigarettes
(++) p < 0.05


[...]

 DISCUSSION

 [...]

 Several studies have now described an association between ETS and BHR, including a recent report on EIB (28). We were unable to demonstrate this relationship in our population. While this may be due to a lack of effect of ETS on BHR in our study population, it could also result from misclassification of exposure and selection bias according to ETS. This may have occurred if parents who smoked were less likely to give permission to study their children, though this did not appear to be the case in our study population.

 We found the presence of a cat in the home to be associated with increased EIB and respiratory symptoms. This is in line with the findings in a New Zealand cohort where allergic skin test sensitivity to cats was an important risk factor for asthma (29) and to the clinic-based report on the high prevalence of cat ownership in people with allergic disorders (30). A somewhat similar study to ours reported to Brunekreef and coworkers (31) did not find this association, though they looked at the effects of all pets combined and speculated that a significant proportion of participants may have disposed of pets for health reasons.

 [...]

 The present results provide evidence suggesting that SES is an important risk factor for EIB and respiratory symptoms that are suggestive of asthma. This further suggests that excess morbidity and mortality from asthma in inner-city areas of large American cities (12) in not only due to differential access to health care but that environmental factors associated with social disadvantage are important. Further research into what these factors might be is needed. In the meantime, public policy changes must also be advocated to improve the health status of poor children.
 
 


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