Abstract
Background
Asthma is the most common chronic illness in children, carrying a major burden. Socioeconomic position (SEP) affects adult asthma outcomes, but its impact on childhood asthma, particularly in primary versus specialist care, has not been studied thoroughly.
Methods
In a Danish cohort consisting of all children aged 2–17 years redeeming inhaled corticosteroids in 2015, parental SEP impact on asthma outcomes was investigated. Workforce attachment, income, education, and metropolitan residence were chosen as covariates in logistic regression. Outcomes were uncontrolled (excessive use of short-acting beta2-agonists), exacerbating (oral corticosteroid use or hospitalization), and severe asthma (according to GINA 2020).
Results
The cohort comprised 29,851 children (median age 8.0, 59% boys). 16% had uncontrolled asthma, 8% had ≥1 exacerbation. Lower income and metropolitan residence correlated with higher odds of poor control, exacerbations, and severe asthma. Lower education correlated with worse asthma outcomes. Education and income were protective factors in primary care, but not in specialist care. Metropolitan residence was the sole factor linked to specialist care referral for severe asthma.
Conclusion
Low parental SEP and metropolitan residence associated with poor asthma outcomes. However, specialist care often mitigated these effects, though such care was less likely for at-risk children in non-metropolitan areas.
Keywords: Pediatric asthma, burden, disparity, referral, pharmacoepidemiology
Introduction
Asthma is the most common chronic disease among children, with an estimated prevalence of 6–9%. It carries a large morbidity burden on both individual and societal levels, primarily driven by uncontrolled disease. 1 The pathogenesis is complex and appears to be a multitude of gene-environment interactions that occur over time, leading to heterogeneous phenotypical presentations. 2 However, certain risk factors have been identified, such as familial predisposition to asthma, maternal smoking during pregnancy, and socioeconomic position (SEP). 3
Socioeconomic position is often defined through measurable traits, such as educational attainment, income, and occupation. These indicators are indirect markers of exposure assumed to be related to asthma development and clinical risk factors, such as tobacco smoke, occupational exposures, limited resources for obtaining controller medication, and lack of health literacy. 4 Some studies have shown a higher prevalence of asthma among children from families with lower SEP,5,6 while others have demonstrated no association or mixed links.7,8 When looking at clinical outcomes of asthma in children, studies have shown that parental SEP strongly impacts the quality of care and asthma control, with children from low SEP families experiencing more exacerbations and daily symptoms and receiving less controller medication.9,10 However, little is known about whether this disparity in disease control is also seen in the context of a free-to-access, tax-funded health care system. Furthermore, the impact of parental SEP on referral to specialist care and asthma outcomes across primary and specialist care settings has been sparsely investigated.
The present study is based on a Danish nationwide cohort (REASSESS Youth) with individual-level data drawn from several national databases and aims to investigate the impact of family SEP on asthma outcomes, severity, and specialist referral among children and adolescents between the ages of 2–17 years. Furthermore, it seeks to distinguish between primary and specialist care when assessing the impact of SEP on asthma outcomes. We hypothesized that there is a socioeconomic disparity in asthma outcomes in children, particularly in primary care settings, and that a lower SEP reduces the probability of being referred to specialist care.
Methods
Study cohort
All children residing in Denmark with actively treated asthma, defined as the redemption of at least two inhaled corticosteroid (ICS)-containing inhalers in a calendar year, were identified in the Danish nationwide REASSESS Youth cohort as previously described. 11 The cohort consists of data provided by Statistics Denmark, the Danish National Prescription Database, and the National Patient Registry. Study approval was granted by the Capital Region of Copenhagen’s Data Safety Board (Ref. P-2021-602).
Data were collected from the first ICS redemption in 2015 (“index date”) and 2 years prospectively for children aged 2–17 at the index date, with any children with less than 365 days of continuous ICS exposure, defined as redemption of at least 365 doses of ICS during the first year of follow-up, being excluded (Figure 1). Using national birth and housing registries, parents were identified and classified as caregiver(s) residing with the child at the index date. A family was defined as any adults (whether biological parents or not) and any children below the age of 18 registered at the same address on the index date.
Figure 1.
Flowchart of study inclusion and exclusion criteria in a nationwide cohort of childhood asthma.
Asthma definitions and classifications
Asthma severity was defined according to the GINA 2020 severity steps according to age at the index date, based on ICS exposure and other controllers used. Possible severe asthma was defined as GINA 2020 Step 3 or 4 with either two moderate or one severe or near-fatal exacerbation in individuals aged 2–11 years. For individuals aged 12+ years, the definition included GINA Step 4 with the above-described exacerbation frequency, or GINA Step 5, regardless of exacerbations.
ICS use was based on redeemed ICS during the follow-up period and stratified as low, low, moderate, or high dose according to the age-appropriate GINA 2020 dosing chart. 12
Disease control was defined according to annualized short-acting β-agonist (SABA) use during the observation period. Excessive SABA use was defined as twice the acceptable control criteria for children aged 11 years and below (2 daily puffs at least 2 days a week, totalling 400 annual doses) or 600 (ages 12+) annual redeemed doses of SABA.1,12
Moderate exacerbations were defined as the redemption of at least 187.5 mg of prednisolone, severe as asthma-related (ICD-10 codes J45, J46, J96, J960 or J969) hospitalisation and near-fatal as intensive care admission with the ICD-10 codes above. The highest severity was recorded if multiple events occurred. Repeated exacerbations within 14 days were discarded as treatment failures, with the highest severity retained.
Specialist management (referral status) was defined children with at least one visit with at a pediatric outpatient clinic coded using the previously described ICD-10 codes during the follow-up period. Any prior visits to a pediatric outpatient clinic were discarded, ergo only children with an active care relation to a pediatric outpatient clinic for asthma were deemed as being followed by a specialist.
Socioeconomic and family definitions
The following socioeconomic position (SEP) markers were used in the analyses, utilizing data from Statistics Denmark:
Workforce attachment
Employed (or self-employed), Currently undergoing education (Enrolled in secondary or tertiary education), Transfer income recipient (Main source of income stemming from welfare transfers) or Retiree or Unclassifiable
Family disposable income
Standardized annual disposable income corrected for any cohabitants to adjust for the economy of scale. 13
Family highest level of attained education
Primary education only (approximately 12 years of mandatory schooling), vocational education (at least 2 years of vocational schooling in addition to primary education), and higher education (at least a bachelor’s degree).
Metropolitan residence
Dichotomous variable for residency in Denmark’s five largest municipalities (Copenhagen and Frederiksberg, Århus, Aalborg and Odense)
Statistical analyses
Descriptive variables were characterized using demographic statistics presented as medians (interquartile range [IQR]). Wilcoxon rank-sum test or χ2-test was used depending on continuous or categorical data for groupwise comparisons.
The present study utilized logistic regression models adjusted for child age and sex to explore the impact of the previously mentioned SEP markers on the outcomes of disease control (excessive use of SABA), exacerbations (any exacerbation during follow-up), and disease severity (possible severe or mild to moderate asthma). Sub-analyses of children in primary versus specialist care were performed, as well as analyses investigating the influence of SEP markers on referral status (primary care vs specialist care). The results are presented as Odds Ratios (OR) with corresponding 95% Confidence Intervals (CI).
R 4.1.3 (The R Foundation, AU) was used for statistical analyses, and Ggplot2 was used to create figures.
Results
In the present study of 29,851 children with actively treated asthma aged 2–17 years, the median age was 8.0 (4.0, 13.0) years, and 59% were boys. A total of 23,987 (80%) children were managed in primary care settings and 5864 (20%) in specialist care settings. High-dose ICS exposure (defined as >400 mcg/>1000 mcg daily beclomethasone equivalent for 2–11 and 12+-year-olds, respectively) was seen in 4958 children (17%), of whom 3531 (71%) were managed in primary care. The use of high-dose ICS seems to follow a bell curve, 8-year-olds serving as the zenith at a 30% prevalence of high-dose ICS exposure (Supplemental Table 1). In primary care, 5885 (25%) children were exposed to daily ICS doses below a low dose, while the corresponding prevalence for children in specialist care was 10%. The median annual SABA use was 200 (100, 360), with 4750 (16%) children having poor disease control based excessive SABA use. The corresponding prevalence rates for primary and secondary care were 3430 (14%) and 1320 (23%), respectively (Table 1).
Table 1.
Demographics of 29,851 children aged 2–17 with actively treated asthma and their families from a nationwide cohort, as well as 1:1-matched control families.
| Overall N = 29,851 | Primary care N = 23,987 | Specialist care N = 5864 | p-value | |
|---|---|---|---|---|
| Child age | 8.0 (4.0, 13.0) | 8.0 (3.0, 13.0) | 10.0 (6.0, 14.0) | <.001 |
| Male child | 17,646 (59%) | 14,064 (59%) | 3582 (61%) | <.001 |
| ICS dose | ||||
| Low | 9541 (32%) | 7793 (32%) | 1748 (30%) | |
| Medium | 8905 (30%) | 6778 (28%) | 2127 (36%) | |
| High | 4958 (17%) | 3531 (15%) | 1427 (24%) | |
| Below low | 6447 (22%) | 5885 (25%) | 562 (9.6%) | |
| Average daily beclomethasone eq. dose (mcg) | 247 (134, 401) | 231 (128, 385) | 334 (205, 468) | <.001 |
| Long-acting beta-2 agonist use | 6894 (23%) | 5139 (21%) | 1755 (30%) | <.001 |
| Leukotriene receptor antagonist use | 6439 (22%) | 4581 (19%) | 1858 (32%) | <.001 |
| GINA step | ||||
| Step 1 | 3865 (13%) | 3465 (14%) | 400 (6.8%) | |
| Step 2 | 9756 (33%) | 8440 (35%) | 1316 (22%) | |
| Step 3 | 9433 (32%) | 7275 (30%) | 2158 (37%) | |
| Step 4 | 6587 (22%) | 4674 (19%) | 1913 (33%) | |
| Step 5 | 210 (0.7%) | 133 (0.6%) | 77 (1.3%) | |
| Annual SABA doses | 200 (100, 360) | 200 (100, 300) | 200 (100, 420) | <.001 |
| Excessive SABA use 2 | 4750 (16%) | 3430 (14%) | 1320 (23%) | <.001 |
| Has had exacerbation(s) | ||||
| Any | 2353 (7.9%) | 999 (4.2%) | 1354 (23%) | <.001 |
| Moderate | 616 (2.1%) | 394 (1.6%) | 222 (3.8%) | <.001 |
| Severe | 1807 (6.1) | 610 (2.5%) | 1197 (20%) | <.001 |
| Asthma severity 3 | ||||
| Mild-to-moderate asthma | 28,421 (95%) | 23,425 (98%) | 4996 (85%) | |
| Possible severe asthma | 1430 (4.8%) | 562 (2.3%) | 868 (15%) | |
GINA: global initiative for asthma.
1Statistics presented: n (%); median (IQR).
2Defined as >400/600 annual doses of short-acting bronchodilators for ages 0–11/12+.
3Defined as GINA step 3 + 4 with two moderate or one severe exacerbation(s) for ages 0–11, GINA step 4 with two moderate or one severe exacerbation(s), or GINA step 5 regardless of exacerbations for ages 12 and above.
In crude analyses by municipality of residence, geographical differences in ICS use, SABA redemptions, the prevalence of exacerbating asthma and specialist referrals for severe childhood asthma was seen (Figure 2). The socioeconomic variables of the children and their families are presented in Supplemental Table 2.
Figure 2.
Municipality of residence-stratified (a) crude mean daily inhaled corticosteroid exposure, (b) crude mean annual short-acting beta-2-agonist use, (c) prevalence of exacerbating asthma and (d) prevalence of specialist referral for children with severe asthma.
Impact of socioeconomic position on disease control and exacerbations
In logistic regression, metropolitan residence was a positive predictor for uncontrolled childhood asthma with an odds ratio (OR) of 1.07 (1.00–1.15). Higher parental education and greater income was associated with lower odds of uncontrolled childhood asthma at ORs 0.82 (0.73–0.93) and 0.82 (0.72–0.93), respectively (Figure 3). Stratified by primary or specialist care management, metropolitan residence was associated with an increased risk of poor control in specialist, but not primary care. Notably, parental education and income remained protective factors in primary care, in contrast to specialist care, where education and income lost statistical significance (Figure 4).
Figure 3.
Odds of (a) severe asthma, (b) poor disease control based on excessive short-acting beta-2 agonist use, and (c) exacerbations based on oral corticosteroid use or hospitalization in 29,851 children aged 2–17 years with persistent, inhaled corticosteroid-treated asthma, adjusted for parental socioeconomic position.
Figure 4.
Odds of (a) severe asthma, (b) poor disease control based on excessive short-acting beta-2 agonist use, and (c) exacerbations based on oral corticosteroid use or hospitalization in 29,851 children aged 2–17 years with persistent, inhaled corticosteroid-treated asthma, adjusted for parental socioeconomic position. Analyses stratified by place of asthma management.
In terms of odds of experiencing exacerbations, a similar pattern was observed with metropolitan residence being associated with higher odds of exacerbations (OR 1.24 (1.13-1.35), while higher education and higher income (2nd, 3rd and 4th quartiles) were associated with lower odds (Figure 3). In the stratified analyses, the association between exacerbations and metropolitan residence was lost in primary care (Figure 4).
Impact of socioeconomic position on childhood asthma severity
In a multivariable adjusted logistic regression model, predictors for having possible severe childhood asthma were male sex (OR 1.14 (1.02–1.28) and metropolitan residence (OR 1.13 (1.01–1.27), whereas higher disposable income (2nd, 3rd, and 4th quartile) was a protective factor (Figure 3). In analyses stratified by place of management, no clear relationship between family income and odds of possible severe childhood asthma was found in either primary or specialist care, whereas metropolitan residence remained a risk factor in specialist care only (Figure 4). The full analyses, including the odds ratios and confidence intervals, are shown in Figures 3 and 4.
Impact of socioeconomic position on specialist referral
Metropolitan residence was found to be a predictive factor for specialist referral across all subgroups eligible for specialist referral or care (e.g., uncontrolled, at-risk (defined as uncontrolled and/or exacerbating asthma) or possible severe childhood asthma) irrespective of the definition used. For subgroups not fulfilling the criteria for severe asthma (e.g., uncontrolled, exacerbating, or at-risk asthma), age, male sex, and parents receiving transfer income were significant predictors of specialist referral (Table 2)
Table 2.
Odds of specialist referral based on parental socioeconomic position for children aged 2–17 with either uncontrolled asthma based on short-acting beta-2 agonist use (n = 4750) or possible severe childhood asthma according to the 2020 global initiative for asthma guidelines (n = 1430).
| Possible severe asthma | Uncontrolled asthma | |||
|---|---|---|---|---|
| OR (95% CI) | p-value | OR (95% CI) | p-value | |
| Male sex | 1.05 (0.83, 1.32) | .7 | 1.17 (1.02, 1.35) | .025 |
| Age | 0.98 (0.96, 1.00) | .11 | 1.10 (1.08, 1.11) | <.001 |
| Family highest education level | ||||
| Basic education | Ref. | |||
| Vocational education | 1.10 (0.73, 1.66) | .6 | 1.00 (0.80, 1.26) | >.9 |
| Higher education | 1.02 (0.66, 1.57) | >.9 | 0.96 (0.75, 1.23) | .7 |
| Family disposable income 2 | ||||
| 1st quartile | Ref. | |||
| 2nd quartile | 1.11 (0.74, 1.68) | .6 | 0.90 (0.71, 1.14) | .4 |
| 3rd quartile | 1.03 (0.69, 1.54) | .9 | 0.89 (0.70, 1.12) | .3 |
| 4th quartile | 0.93 (0.61, 1.41) | .7 | 0.88 (0.68, 1.13) | .3 |
| Family highest socioeconomic position | ||||
| Employed/self-employed | Ref. | — | ||
| Currently undergoing education | 0.66 (0.15, 2.94) | .6 | 1.37 (0.73, 2.49) | .3 |
| Transfer income recipients | 1.71 (1.01, 2.95) | .051 | 1.42 (1.07, 1.89) | .014 |
| Retirees or unclassifiable | 0.83 (0.13, 6.49) | .8 | 1.54 (0.49, 4.62) | .4 |
| Metropolitan residence | 1.64 (1.29, 2.08) | <.001 | 1.19 (1.03, 1.37) | .015 |
1Statistics presented: n (%); median (IQR).
2Quartiles calculated according to the Danish national population’s disposable income for the case’s index year.
Impact of socioeconomic position on ICS dose exposure
When stratifying ICS dose exposure by parental SEP, 18% of children of employed caregivers were exposed to high daily doses of ICS, whereas it was 9% for children of parents in the most disparate workforce attachment category (retirees and/or unclassifiable). Similar patterns were found irrespective of the definition of high SEP, with 18% of children whose caregivers had higher education receiving high-dose ICS, whereas the number was 12% for children whose caregivers had primary education only (Supplemental Figure 1).
Discussion
In the present study, we aimed to investigate the impact of family socioeconomic position (SEP) on asthma outcomes, severity, and specialist referral among 29,851 children and adolescents between the ages of 2–17 years. Furthermore, we sought to distinguish between primary and specialist care when assessing the impact of SEP on asthma outcomes. We found that metropolitan residence was associated with higher odds of uncontrolled childhood asthma, exacerbations, and severe asthma as well as being referred to specialist care. In general, greater income adequacy and higher education level were associated with lower odds of adverse asthma outcomes and asthma severity but were not associated with increased odds of specialist referral. When stratifying between primary and specialist care, high parental education and income remained protective factors in primary care, in contrast to specialist care, where the impact of parental SEP was diminished and, in most cases, lost statistical significance.
Inhaled corticosteroids and management
According to the GINA guidelines, children who receive high-dose ICS daily should be managed in specialist care. 1 In the present study, 71% of the children exposed to high-dose ICS were managed in primary care, demonstrating a discordance between clinical practice and guideline recommendations. Our finding that 16% of the children had excessive SABA use is consistent with the findings of Butz et al., 14 who found that 16% of the children had excessive SABA use. Melén et al. 15 found a markedly higher proportion of children with excessive SABA use, 25–45%, but this can in part be explained by differences in definitions of excessive SABA use.
Impact of socioeconomic position on disease control and exacerbations
The lower odds of poor disease control and exacerbations in children of parents with higher income and education is in line with the previous findings of Cope et al., 16 who found that greater income adequacy is associated with better disease control and fewer exacerbations. Cope et al. 16 found that children of high-income families had significantly better disease control than those of low-income families, measuring asthma control across six self-reported control parameters, in contrast to the present study which utilises SABA prescription redemptions as an indicator for asthma control. However, similar findings across study designs strengthen the association between SEP and disease control.
Income has repeatedly been suggested as an important determinant of controller medication use, leading to underutilization and poorer control in low-income families,17,18 and Kozyrskyj et al. 19 found a direct relationship between income and ICS use in a system of universal healthcare for children. These findings are consistent with the results of the present study, in which we found socioeconomic disparity in exposed ICS dose. As income and education levels are often correlated, this could partly explain the protective associations of higher education. However, other studies have highlighted the importance of medication beliefs and health literacy as ways in which educational level could affect ICS use, independently of income. For example, an individual with a higher educational level may be more receptive to information regarding positive health-related choices. 18
Interestingly, when stratified between primary and specialist care, the impact of income and education level diminished and often failed to reach statistical significance in specialist care. The evidence in this field is sparse, yet possible mechanisms could include additional resources to focus on ICS adherence, instructions on inhaler use, parental support, and regular, systematic check-ups. Our findings suggest that repeated patient/parental education and support could have a larger impact on families with lower SEP, should their health literacy and agency be lower than those with higher SEP.
Impact of socioeconomic position on childhood asthma severity
Metropolitan residence is a well-known risk factor for exacerbations, with several studies showing strong links between outdoor air pollution and asthma emergency room visits.20,21 Conversely, other studies state that the association between metropolitan residence and asthma severity is mediated by socioeconomic factors, such as clusters of deprived neighbourhoods and poor housing conditions, rather than outdoor air pollution. 22 Indeed, Groot et al. 23 found that socioeconomic position was strongly related to indoor home environments, with higher income and educational strata having healthier indoor environments with less second-hand smoke, mould, and condensation. Additionally, one could hypothesize that children in metropolitan areas are more likely to be treated in hospitals because of shorter distances to hospitals, and thus get their exacerbations registered in official records and an in-hospital referral to specialist care, as opposed to children in rural areas.
Impact of socioeconomic position on specialist referral
The fact that metropolitan residence is strongly associated with higher odds of being referred to a specialist is consistent with the findings of Håkansson et al., 24 who studied referral patterns among adults with asthma. Our study addresses a similar gap in the knowledge regarding childhood asthma. A Taiwanese study on the rural-urban divide in specialist care for gastrointestinal diseases states that a possible explanation could be that specialists are often concentrated in larger cities in outpatient clinics situated in larger hospitals, which makes it more time-consuming and inconvenient for patients living in rural areas. 25 Our findings suggest that similar issues may exist in pediatric asthma patients.
Interventions for the impact of socioeconomic position on asthma outcomes
Given the fact that ICS use is crucial for disease control and that ICS use has been directly associated with family income, it is logical to think of income as the main way in which SEP impacts asthma outcomes. Thus, focusing on interventions that increase ICS adherence, especially among children from low-income families, may diminish the socioeconomic disparity in asthma outcomes. An example of such an intervention could be a nurse-led educational intervention; however, this type of intervention has shown mixed results, with one study reporting successful improvement of control and daily activities 26 and another study showing no impact. 27 Another intervention was explored in a Swedish study by Dahlén et al., 28 in which asthma medication for children was made available without patient fees. The study observed only a modest increase in the proportion of children on persistent asthma medication, further casting doubt on the singular role of income in how SEP affects asthma outcomes.
Limitations
There are several limitations to our observational study, related to the study design and the availability of data. First, the inclusion criteria were based on the redemption of ICS and thus excluded SABA-only treated children, which limits generalizability. Second, excessive SABA use does not necessarily equal poor disease control and should ideally be compared to self-reported symptoms, as SABA could also be used in relation to physical exercise or because of symptoms of viral infections. Third, ICS is sometimes used for other indications such as viral wheezing or asthmatic bronchitis, which could affect the results. This indication, however, is mostly used for children below the age of 3 years and is therefore not expected to significantly affect the results. Fourth, ICS and SABA exposure is based on redeemed doses, which may be affected by stockpiling inhalers or redemption of multiple inhalers in two-household families, leading to overestimation, through arguably annualization of 2-year data should reduce the impact of multiple redemption(s). Fifth, due to limitations in the Danish National Prescription Database, a small number of moderate exacerbations for children <6 years using low doses (total dose <125 mg) of prednisolone have been excluded, however removing the total dose criteria from prednisolone redemptions yields <5% additional exacerbations and thus the impact was deemed negligible. Despite these limitations, we would like to emphasize the strengths of the REASSESS Youth cohort, which include a high degree of data completeness, universal linkage between children and parents, and robust, non-biased data capture due to legal requirements to submit data to Statistics Denmark from the various sources used.
Conclusion
This study found substantial socioeconomic disparities in asthma outcomes between children and adolescents. Low parental socioeconomic position and metropolitan residence were predictors of poor disease control, exacerbations, and severe asthma. Furthermore, the impact of parental socioeconomic position on asthma outcomes was diminished in specialist care, as opposed to primary care. Metropolitan residence was the sole predictor of referral for specialist care.
Supplemental Material
Supplemental Material for Impact of family socioeconomic position on childhood asthma outcomes, severity, and specialist referral – a Danish nationwide study by Martino Renzi-Lomholt, Charlotte Suppli Ulrik, Deepa Rastogi, Jens Ulrik Stæhr Jensen and Kjell Erik Julius Håkansson in Journal of Chronic Respiratory Disease.
The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: MRL declares no conflicts of interest. KEJH has received personal fees from AstraZeneca, Chiesi, GSK, Sanofi and TEVA. DP declares no conflicts of interest but does serve on a DSMB for the National Institute of Health. CSU has received personal fees from AstraZeneca, GSK, TEVA, Chiesi, Sanofi Genzyme, Boehringer-Ingelheim, Orion Pharma, Novartis, ALK-Abello, Mundipharma, Berlin Chemie, Pfizer and Actelion outside the submitted work.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present work was funded by the Børnelungefonden, Trial Nation Denmark Respiratory, Respiratory Research Unit, Hvidovre Hospital, and SanofiGenzyme. All grants were unrestricted research grants, and grantors were not involved in any aspects pertinent to planning, conducting, analysing, or presenting the present study results.
Supplemental Material: Supplemental material for this article is available online.
ORCID iDs
Martino Renzi-Lomholt https://orcid.org/0000-0001-6219-9367
Charlotte Suppli Ulrik https://orcid.org/0000-0001-8689-3695
Jens Ulrik Stæhr Jensen https://orcid.org/0000-0003-4036-0521
Kjell Erik Julius Hakansson https://orcid.org/0000-0001-5804-0740
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Supplementary Materials
Supplemental Material for Impact of family socioeconomic position on childhood asthma outcomes, severity, and specialist referral – a Danish nationwide study by Martino Renzi-Lomholt, Charlotte Suppli Ulrik, Deepa Rastogi, Jens Ulrik Stæhr Jensen and Kjell Erik Julius Håkansson in Journal of Chronic Respiratory Disease.