Socioeconomic factors and prescription of antibiotics in 0- to 2-year-old Danish children

Nana Thrane1,3,*, Charlotte Olesen1, Henrik Carl Schønheyder1,4 and Henrik Toft Sørensen1,2

1 Department of Clinical Epidemiology, Aalborg Hospital and University of Aarhus, Vennelyst Boulevard 6, DK 8000 Aarhus C; 2 Danish Epidemiology Science Centre, Department of Epidemiology and Social Medicine, University of Aarhus, Aarhus; 3 Department of Pediatrics, Herning Central Hospital, Herning; 4 Department of Clinical Microbiology, Aalborg Hospital, Aalborg, Denmark

Received 25 June 2002; returned 11 September 2002; revised 8 October 2002; accepted 6 December 2002


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Objectives: The aim was to examine the impact of socioeconomic factors on the use of systemic antibiotics during the first 2 years of life.

Methods: This was a population-based cohort study of 5024 Danish children born in 1997. The study was conducted by linking records drawn from public administrative registries. The main predictor variables were mother’s education level, household income and cohabitation status. The outcome was the number of antibiotic courses (0, 1–5, >=6) during the first 2 years of life.

Results: A total of 3273 children (65.1%) received 1–5 antibiotic courses, and 337 (6.7%) received >=6 courses of antibiotics during the first 2 years of life. The risk of receiving >=6 courses of antibiotics was increased in children of mothers with a low educational level (<=10 years) compared with vocational education [OR 1.3 (95% CI 1.0–1.7)]. Children of mothers with a higher education >4 years had a reduced risk of receiving >=6 courses [OR 0.3 (95% CI 0.1–0.7)]. Children from high-income families had a reduced risk (not statistically significant) of receiving antibiotics, compared with children from middle-income families [1–5 and >=6 courses: adjusted OR 0.6 (95% CI 0.3–1.2)]. Children of single mothers had an increased risk of receiving antibiotics, particularly if the child did not attend day care.

Conclusions: Socioeconomic factors have some impact on antibiotic prescription in young children. Children of mothers with only basic schooling were at highest risk of receiving multiple prescriptions, whereas children of mothers with a high education, and/or high household income, had the lowest risk.

Keywords: socioeconomic factors, systemic antibiotics, infectious diseases, children


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Infections are the most frequent diseases in childhood, and systemic antibiotics account for one-third of all prescriptions in pre-school children.13 Recent studies report that 11% of Danish children and ~40% of children from the USA under 3 years of age receive three or more prescriptions during a year.4,5 It is important to identify factors associated with high use of antibiotics, since the underlying infection may cause discomfort, long-term complications68 and have economic consequences.9,10 Moreover, the use of antibiotics is associated with antimicrobial resistance, which is a major menace in the treatment of infection the world over.11,12

A low level of education, and unemployment among parents, have been associated in their children with a greater risk of acute lower respiratory tract infection and otitis media.1316 The majority of infections in early childhood are of viral origin,14 and generally, antibiotics are prescribed for the most severe. However, data are rare on the association between socioeconomic status and use of antibiotics.17,18

In this population-based follow-up study, we examined the association between socioeconomic factors in the family (mother’s educational level, household income, cohabitation status) and the child’s risk of receiving antibiotics (1–5, >=6 courses) during the first 2 years of life.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The study population included all children born during 1997 in North Jutland County, Denmark, and who lived in the county during their first 2 years of life (n = 5641). We extracted data from the North Jutland Birth Registry, which includes information on all pregnancies and births recorded by the midwives. Children who died during the study period were excluded (n = 40); 32 having died before they reached the age of 4 months. North Jutland County has 27 municipalities. We had no access to day care data from five municipalities (10.9%) due to refusal to participate in the study, or lack of accessible registries, leaving 5024 children for the final analyses. The study cohort was established by record linkage of information from the registries, using the unique personal identification number given to each Danish citizen at birth.

Education

We extracted data from the National Statistical Office of Denmark19 (registered November 1996) on the mother’s highest educational level (completed or ongoing): basic schooling <=10 years, advanced schooling equivalent to 11 or 12 years, vocational education and training for 1–3 years, higher education for 1–4 years and higher education for >4 years. Higher education requires a minimum of 12 years schooling. We chose a vocationally educated group as a reference. Data on the education of the mothers of 33 children (0.7%) were missing and excluded from the analyses.

Income

We obtained data on household income from the National Statistical Office of Denmark:19 <135 000 DKK (~5% of the population), 135 000–307 000 DKK (~20% of the population), 308 000–459 000 DKK (~50% of the population), 460 000–620 000 DKK (~20% of the population) and > 620 000 DKK (~5% of the population). We chose the middle income group as a reference. Data on the income of mothers of 186 children (3.7%) were missing and excluded from the analyses.

Cohabitation status

Data from the North Jutland Birth Registry included parental cohabitation status, i.e. the mother living alone or cohabiting with the father during the early stages of pregnancy (yes/no).

Prescriptions

The outcome measure was the number of antibiotic courses redeemed during the first 2 years of life: 0, 1–5, >=6 for each child (one antibiotic course includes prescriptions redeemed within a period of 0–10 days).20 We used the National Health Service to identify all prescriptions of systemic antibiotics [anatomical therapeutic chemical (ATC) code J01] during the period 1 January 1997–31 December 1999. In Denmark, antibiotics are purchased on prescription only, and only in hospitals is administration intravenous. All prescription drugs are sold through monopolized pharmacies, equipped with computerized accounting systems linked to the Danish National Health Service. The latter provides tax-supported health care for all citizens and reimburses 50–75% of the cost of most prescribed drugs.

We had no information on drugs not subsidized by the National Health Service, such as cephalosporins and tetracyclines. The relevance of these drugs is negligible: cephalosporins accounted for only 0.2% of the total defined daily doses of antibiotics sold in Denmark during 1996,21 and tetracyclines are not recommended for children under 8–12 years of age.22

Other risk factors for antibiotic use

Potential confounding from the following variables was examined in the statistical analyses. Data from the North Jutland Birth Registry included gender, birth weight, gestational age, the mother’s age at time of delivery, her smoking habits in early pregnancy and the existence of older siblings in the home.

We used the North Jutland Hospital Discharge Registry to examine other diseases that may have influenced the risk of prescription antibiotics: respiratory distress in the perinatal period and heart disease.

In Denmark, public day care is administered by the municipalities and organized as day care homes with a single child-minder, or as day care centres. Information on day care settings for the 5024 children was obtained for 1 January 1997–30 June 1999 from the municipality registries.

Statistical methods

We used Cox regression models to estimate the cumulative incidence rate ratio for boys compared with girls. Adjustment for potential confounders did not change this risk estimate. The assumption of proportional hazards was assessed graphically by comparing observed versus predicted values of survival probabilities.

We examined the crude association between socioeconomic factors (mother’s education, household income, cohabitation status) and number of antibiotic courses (0, 1–5, >=6) by contingency tables. The Cox regression model is based on time to event, e.g. first hospitalization. Our main purpose was to examine the frequency of prescriptions over a period of time in relation to socioeconomic factors. Therefore, the associations were presented as odds ratios (ORs), with a 95% confidence interval (CI) using multinomial logistic regression.23 For each of the exposure variables, we examined the influence of potential confounding factors and two other socioeconomic variables. We fitted a logistic regression model, which included only variables that changed the bivariate ORs by >10%.24

For each of the socioeconomic variables, we combined stratified analysis with logistic regression analysis to examine variations in risk estimates across strata, i.e. effect modification. The stratification was subsequent to all other risk factors for antibiotic use, and for two other socioeconomic variables.

The Hosmer Lemeshow’s goodness-of-fit test was used to assess the fit of the model, using the individual logistic regressions approach.23 Data analyses were performed in SPSS, version 10.0 (SPSS, Chicago, IL, USA).


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
We recorded 10 983 systemic antibiotic prescriptions. The cumulative incidence of receiving prescription antibiotics was 45.6% during the first year and 71.8% during the first 2 years of life. The cumulative incidence rate ratio was 1.5 (95% CI 1.3–1.7) for boys compared with girls (Figure 1). During the first 2 years of life, 3273 (65.1%) of the 5024 children received 1–5 courses, and 337 (6.7%) received >=6 courses of antibiotics. Table 1 shows the characteristics of the children in the cohort.



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Figure 1. Kaplan–Meier survival curve (1–S). Cumulative incidence of proportion of children who received at least one prescription of antibiotics according to age and gender.

 

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Table 1.  Characteristics of children in the cohort (n = 5024), and number of courses of systemic antibiotics during the first 2 years of life (%)
 
The risk of receiving >=6 courses of antibiotics was higher in children from families where the mother had basic school education, compared with vocational education (Table 2). The risk of receiving antibiotics was 30–40% lower in children of mothers with 11–12 years of schooling. Children of mothers with >4 years higher education had a reduced risk of receiving >=6 courses of antibiotics. Adjusting for potential confounders did not change the risk estimates in the multivariate model. The analyses were also conducted with the highest parental education level (either father or mother) as the predictor variable; this made no difference to the results.


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Table 2.  Association between mother’s level of education, household income, marital status and prescription of systemic antibiotics during the first 2 years of life
 
Children from high-income families had a decreased risk of receiving prescriptions, compared with the middle level of income (Table 2). None of the following factors: birth weight, gestational age, gender, day care, siblings, other diseases (respiratory illness in perinatal period or heart disease), mother’s education, mother’s smoking during pregnancy or mother’s age confounded the estimates.

Children from families where the mother was single had an increased risk of receiving antibiotics, compared with children from families where the mother was cohabiting with the father (Table 2). Stratified analyses showed that the effect of being single was highest among children not attending day care [1–5 courses: adjusted OR 2.6 (95% CI 1.0–7.0); >=6 courses: adjusted OR 3.2 (95% CI 0.6–17.0), not statistically significant] (data not shown). None of the following factors: birth weight, gestational age, gender, day care, siblings, other diseases (respiratory illness in perinatal period or heart disease), mother’s age or household income confounded the estimates.

We found no substantial sign of an interaction between socioeconomic factors and other risk factors for use of antibiotics, i.e. gender, siblings or smoking during pregnancy.


    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Children of mothers with a low educational level had a slightly higher risk of receiving multiple courses (>=6) of systemic antibiotics during the first 2 years of life, compared with children of vocationally educated women. Children from high-income families had a reduced risk of receiving antibiotic courses compared with children from middle-income families. Children from families with single mothers had an increased risk of receiving antibiotics, in particular if the child did not attend day care.

The population-based design, where children were followed from birth by prospective data collection on an administrative basis, minimizes selection bias due to loss of follow-up. The validity of data from the National Statistical Office of Denmark and the North Jutland Birth Registry is high.19,25 The information on exposure (education, income and marital status) was obtained at a fixed time, and some of the mothers may have changed status during the first years of the child’s life. This bias will attenuate the risk estimate.

The registry data were collected independently of the research question, which left less room for certain types of bias (recall, non-response, the knowledge of being under study affecting physicians’ behaviour). Records of antibiotic prescription may not have been complete, as children may have redeemed prescriptions while absent from the county (<2%), and inpatient use was not recorded. However, most children are discharged from hospital with a prescription before the end of the treatment period.

Information on major possible confounding factors was available, although we lack information on duration of breast-feeding, which is associated with both socioeconomic factors and risk of infectious disease.14

Our ability to link information on antenatal, perinatal and socioeconomic factors to subsequent antibiotic prescription for a large group of infants has rarely been achieved for other populations. Thus, few published data are available for comparison. In contrast to our findings, Hjern et al.18 reported that children in Swedish families of low social status were less likely to have taken antibiotics during the past 12 months. This may be explained by the fact that children in Swedish low social status families less often attended day care. Recall bias and a non-response rate of 18.8% may also contribute to the results, if low status families with high antibiotic use refused to participate in the study. Another Swedish study reported that children of non-manually working parents had an increased risk of receiving antibiotic prescriptions compared with manually working parents.17 However, this study covered only 76 children, and the measure of socioeconomic status was dichotomous: manual working yes/no. The reduced risk in children of mothers with a high income may be explained by the strong correlation with high education. The level of income is not as strongly correlated with income in other education categories.

How does socioeconomic status affect the risk of receiving prescriptions? We discuss two explanations: the frequency of infectious morbidity and the threshold for prescribing.

Our findings are in accordance with studies of infectious morbidity in relation to family education level.2628 The greater risk of infectious illness among people of lower socioeconomic status is thought to be attributable to increased exposure to infectious agents, for example due to crowding or hygiene procedures, and decreased host resistance to infection, for instance as a result of poor nutrition, smoking or stress.13 In our study, adjusting for smoking and crowding (siblings, day care) did not change the risk estimates, but we had no information regarding nutrition or stress. The effect of education may be explained by a greater incidence of breast-feeding among the highly educated women, or a better knowledge of hygiene procedures. However, our study included a limited number of highly educated women. We found the risk of antibiotic courses lower in children with mothers who had 11–12 years of schooling than in the group with a higher education of 1–4 years. This is surprising, since the latter requires basic schooling of 11–12 years.

The variation in antibiotic prescription practices may be due to the different clinical and therapeutic attitudes of general practitioners.29 The decision to prescribe a drug or not may be influenced by the symptoms presented, the extent of scientific evidence as a basis for decision making and the patient’s (family’s) attitude towards, or demand for, a certain treatment.30,31

Previously, we reported an increased risk of antibiotic prescription in children enrolled in day care settings.32 In accordance with our study, Hjern et al.18 reported that children from single-parent families had an increased risk of receiving antibiotics, particularly in children not attending public day care. This finding may be explained by a weaker social network for these families, which leads them to the physician more often compared with families with two cohabiting parents.

Our study showed that socioeconomic factors have some impact on antibiotic prescription in young children. Children of mothers with only basic schooling, which accounted for 28% of the population, had the highest risk of receiving multiple prescriptions, whereas children of mothers with a high education and high household income had the lowest risk.


    Acknowledgements
 
We thank the staff at the Department of Health Insurance and Preventive Medicine, and Hospital Registries in the County of Northern Jutland, for excellent assistance in preparing the data for analyses. This work received assistance from the National Centre for Register-based Research, funded by the Danish National Research Foundation. The study was funded by Helsefonden, the Fund for Medical Science Research (Fonden til Lægevidenskabens Fremme), Rosalie Petersens Fund, the Sociomedical Research Fund (Den Samfundsmedicinske Forskningsfond) and the Western Danish Research Forum for Health Sciences (Vestdansk Forskningsforum). The activities of the Danish Epidemiology Science Centre are financed by a grant from the Danish National Research Foundation.


    Footnotes
 
* Corresponding author. Tel: +45-8942-6076; Fax: +45-8613-1580; E-mail: n.thrane{at}dadlnet.dk Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
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