Factors associated with medication adherence in school-aged children with asthma

Discussion

This study investigated factors associated with adherence in children presenting to a regional emergency department with an asthma exacerbation. Electronically monitored adherence was poor with median adherence being 30%, a rate similar to other studies in children at high risk of non-adherence [25–27] but lower than the average reported adherence from studies using electronic monitoring and when compared to other developed Western countries [3, 8]. We examined a number of factors that have previously been associated with adherence, such as ethnicity [13, 28] and asthma knowledge [10], as well as factors not previously investigated, such as learning style. Of the variables examined in this study, only a few were significantly associated with adherence.

Ethnicity had a strong association with adherence, with Asian participants having the highest overall adherence (47%). The reason for this is unclear. There is little literature available on adherence for ethnic groups in New Zealand beyond Māori, Pacific and European populations. Education studies in Australia show that Asian students are more compliant with orders from teachers than other ethnic groups [29] due to respect and perceived dominance of the teacher [30]. The healthcare provider–patient relationship may be associated with a similar respectful or submissive response, which may enhance adherence. Māori children had the poorest adherence (median adherence 19%), followed closely by New Zealand European (26%) and Pacific peoples (28%). From studies in mild-to-moderate asthmatics, Māori and Pacific children show poorer asthma control than other ethnic groups [31] due to under treatment and poor adherence with preventive treatment [31, 32]. Therefore, the ethnic differences in our study were unexpected, as although adherence rates for New Zealand Europeans were higher than Māori children, they were lower than that of other minority ethnic groups. The participants in our study attended the emergency department for asthma and therefore represent those with the poorest asthma control and adherence [27]. This suggests that the effect of ethnicity may be different in those with poorly controlled asthma and at high risk of non-adherence, but more research is needed to confirm this. We note that the adherence rate in our population of high-risk children was particularly low when compared to populations recruited from outpatient clinics [12, 33–37], and more similar to those recruited from tertiary centres or hospitals [38]. Indeed, in adults, Krishnan et al. [39] reported a drop in inhaled corticosteroid use to ∼50% within a week of hospital discharge after an asthma exacerbation. This highlights the potential vulnerability of patients presenting to tertiary care settings and the importance of considering the contribution of this as a potential marker of poor adherence. The high-risk nature of a population presenting to the emergency department with asthma may override the usual effects of other adherence determinants, such as ethnicity, as seen in our study.

Female sex was significantly associated with better adherence in our study. The relationship between sex and adherence is inconsistent in the literature, with many studies showing no association [9, 40, 41]. Only one study has reported an association between female sex and higher adherence in adult asthma [42]. In other chronic conditions, female sex has been linked with poorer adherence in adolescents [43]. Mental health and coping strategies may mediate the relationship between sex and adherence [43], but we did not measure psychological factors.

No clear relationship was found between socioeconomic status, determined by NZDep scores, and adherence. Some studies have reported a lack of correlation between adherence and general socioeconomic status, family income or qualifications of the primary caregiver [35, 44], although others report low adherence rates in those with poor socioeconomic status [3]. Compared to studies that report higher overall adherence, the population in our study did incline towards higher deprivation scores (mean deprivation 6 out of 10). We found a significant relationship between household size and adherence, a factor seldom studied in asthma. Kyngäs [45] found that adherence improved with increasing number of siblings and similarly Lieu et al. [46] reported better adherence in larger families. Our study found the opposite effect, with larger household size associated with poorer adherence. It is possible that larger families present more competing demands, thus limiting the time available to manage a child's asthma [47] and increasing forgetfulness, a key reason for non-adherence in childhood asthma [48]. This negative effect of family size on adherence may be more pronounced in our study as over half of the participants were aged <8 years of age. Previous studies have demonstrated that younger children have the majority of their medications managed by their parents [4, 47, 49], which may contribute to poorer adherence with increased household size. This is also supported by the negative relationship seen between asthma responsibility scores and adherence, where adherence decreased with increasing child responsibility for their own asthma management, though the relationship did not reach statistical significance.

The relationship between age at diagnosis and adherence is unclear; the few studies investigating this relationship have not found any association [40, 41]. Our study found age at diagnosis was a significant factor, with a reduction in adherence of 3% per increasing year of age at diagnosis. There was a corresponding nonsignificant trend between age of the child and adherence, with adherence being worse in older children, similar to previous findings [2, 4, 44, 45, 50]. This may, in part, explain the association between age of diagnosis and adherence. The association between increased age and worsened adherence might also explain the overall low adherence seen in this population. Most previous studies that have reported higher adherence have included much younger age range, from as young as 15 months [3]. Disease duration may play a role as those with a younger age of onset have more opportunity for habit formation for medication adherence [51]. Conditioning may lead children or their parents to believe that asthma is a long-term condition requiring long-term preventive treatment and, as a result, lead to better adherence. Indeed, adherence is higher in those that believe asthma is a long-lasting condition [42].

This is the first study investigating the impact of learning style on adherence. A link between the two is plausible given that learning style is associated with behaviour [14, 15], but no association was found in either the group receiving the auditory intervention or control. This may be due to the difficulties in characterising learning styles in children as younger children tend to have multimodal learning styles rather than a single learning modality [23]. The lack of a validated tool for assessing learning style in the younger age groups in our study may have also limited the accuracy of determining the child's learning style. Although a relationship between learning styles and adherence was not found, there is a possibility that interventions tailored to an individual's learning style may be more successful. The literature supports interventions that are personalised to an individual [3, 8]; future research should investigate the usefulness of incorporating learning style into the intervention tailoring process.

Of the factors that were investigated, only four were found to be significantly associated with adherence. However, these factors still only explained 30% of the variance seen in adherence. Although a wide range of adherence determinants were examined, we did not investigate the effect of illness perceptions [52–57] or medication beliefs [12, 50, 58–62], which are thought to be more powerful determinants of adherence [57] than sociodemographic and clinical factors in adults. In children, the review by Drotar and Bonner [63] of studies investigating the factors associated with adherence in children reports that parental and, to a lesser extent, child beliefs demonstrate significant relationships with adherence. Medication beliefs and illness perceptions were not measured in our study but future research should include them in order to develop a clearer understanding of the extent to which these may explain adherence behaviour in children with poorly controlled asthma and to investigate how these may interact with the adherence determinants identified in our study.

The generalisability of our study results may be limited by data collection in a single centre and country. Nevertheless, our study population were representative of the total population presenting to the emergency department with asthma, as described previously [16], and included a wide range of ethnic and socioeconomic groups. Due to missing data we excluded 14 participants from the multivariable analysis, which could have led to selection bias. However, bias as a result of this exclusion is unlikely as our sensitivity analysis, where variables with missing data were excluded rather than participants, showed similar results. Questionnaires were administered in the presence of research personnel, which may have affected the reliability of the data collected. A small number of participants chose not to complete some questions, but the numbers with missing data were low and unlikely to affect our results. The application of these findings to the design of adherence interventions may be limited, as the adherence determinants identified were largely non-modifiable. Nevertheless, our findings add important information to the literature on factors that contribute to poor adherence in children, particularly in those with poorly controlled asthma. As the factors identified from our study are easily quantifiable, they may be used to help prioritise those at greatest need for intervention. Our work sets a platform for further research into how potentially modifiable adherence determinants, such as medication beliefs, may be related to non-modifiable factors such as ethnicity or duration/experience in managing asthma, and how these non-modifiable factors may serve as proxies for identifying those who are most at risk of poor adherence.

In summary, female sex, Asian ethnicity, smaller household size and younger age at diagnosis were strongly associated with better preventive medication adherence in children with poorly controlled asthma presenting to a regional emergency department. These factors explained only 30% of the variation in adherence, highlighting the difficulty of identifying adherence barriers in this age group. There was no association between adherence and learning styles. Further research in other emergency department populations is needed. Given the combination of poor adherence and high risk for life-threatening asthma in children presenting to the emergency department, there is an urgent need to identify the specific adherence barriers and develop effective interventions for this population of children.