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The American Journal of Managed Care January 2016
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Effects of Continuity of Care on Emergency Department Utilization in Children With Asthma

Shu-Tzu Huang, MS; Shiao-Chi Wu, PhD; Yen-Ni Hung, PhD; and I-Po Lin, PhD
Better continuity of ambulatory asthma care can reduce the risk of asthma-related emergency department visits for children with asthma in Taiwan.


Objectives: To examine whether continuity of ambulatory asthma care can lower asthma-specific emergency department (ED) utilization by children with asthma in Taiwan.

Study Design: Retrospective cohort study based on claims data.

Methods: We used the Taiwan National Health Insurance Dataset, 2006 to 2009. The study population was new asthma patients aged 0 to 17 years in 2007, and every case was observed for 2 years. We used the Continuity of Care Index (COCI) to calculate the continuity of ambulatory asthma care in the first year, and estimated the asthma-specific ED utilization in the second year. Two-part hurdle regression was used for statistical analysis.

Results: The 29,277 patients in our study had an average COCI of 0.68 (± 0.31), and 42.3% of patients had an index of 1. More than 1 in 20 patients—1641 (5.61%)—had at least 1 asthma ED visit, and the mean number of visits per user was 1.46 (± 0.99). After controlling for covariates, the groups with medium and low continuity of ambulatory asthma care had 21% (odds ratio [OR], 1.21; 95% CI, 1.06-1.39) and 38% (OR, 1.38; 95% CI, 1.21-1.58) higher asthma-related ED utilization, respectively, than the group with high COCI. However, among users, the number of ED visits was not statistically correlated to the continuity of ambulatory asthma care.

Conclusions: High continuity of ambulatory asthma care can decrease asthma-specific ED utilization risk in children with newly diagnosed asthma in Taiwan. We suggest that providers and the government reinforce the use of follow-up care and education for high-risk groups to improve the continuity of ambulatory asthma care.

Am J Manag Care. 2016;22(1):e31-e37

Take-Away Points
This was a retrospective cohort study using Taiwan’s National Health Insurance Dataset, aimed to examine the effects of continuity of ambulatory asthma care on asthma-related emergency department (ED) utilization for children with asthma. We used 2-part hurdle regression.
  • For the first part, higher continuity of ambulatory asthma care significantly decreased the risk of having asthma-specific ED visits.
  • For the second part, which examined the asthma-specific ED users only, continuity of ambulatory asthma care did not significantly correlate with the number of visits.
  • Better continuity of ambulatory asthma care might improve outcomes for children with asthma.
Asthma is among the most common respiratory diseases, with 300 million affected people worldwide, according to the World Health Organization.1 About 1 in 10 American children suffered from the disease in 2009.2 Children with asthma are prone to acute, sometimes severe, attacks. Between 2005 and 2007, US children with asthma visited the emergency department (ED) 9.9 times per year on average, compared with the average 7.5 annual visits for US patients with asthma of all ages.2

The US Agency for Healthcare Research and Quality has indicated that surveillance of asthma care should include daily symptom burden and acute avoidable events due to asthma, such as asthma ED visit rate and asthma admission rate. In particular, asthma ED visits reflect poor disease management on the part of providers and patients.3

The US Institute of Medicine defines continuity of care (COC) as the condition of “care over time by a single individual or team of health professionals.”4 Within this long-term relationship, healthcare providers can better manage the chronic conditions of their patients because of their familiarity with their patients’ medical history and greater ability to communicate with their patients because of repeat interactions. COC leads to greater patient satisfaction; less disability and pain; and decreased ED utilization, hospitalization, and medical costs.5-8

For patients with asthma, research has shown that higher continuity of asthma care can decrease asthma ED utilization.9-12 However, most of these investigations were conducted in Western countries; COC has not been well studied in Asian children with asthma. We therefore aimed to examine whether continuity of ambulatory asthma care could lower asthma ED use among children with asthma in Taiwan. We adopted 2-part hurdle regression models to analyze the data for all children with asthma, and separately for those who had ED visits.


Data Source

In 1995, Taiwan implemented a single-payer, compulsory national health insurance (NHI) program that now enrolls nearly 100% of residents. Universal insurance coverage and low co-payments minimize the economic barrier to care for patients. With no gatekeeper program, patients choose the provider of their choice.

The NHI data set is a national, population-based healthcare claim database containing detailed records of outpatient visits, ED visits, and hospital admissions (including diagnosis, procedures, medication, provider information, and expense). We used the data for 2006 to 2009. By using secondary data analysis, approval from an institutional review board was not necessary for this study.

Study Design and Study Subjects

We conducted a retrospective cohort study of new patients with asthma aged under 18 years in 2007. New asthma patients were defined as those having 2 outpatient or ED visits, or 1 admission, due to asthma (The International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] code for primary diagnosis of 493.XX) in 2007 but without such records in the previous year.12,13 The date of the patient’s first asthma visit/admission was called the index date, and all patients were observed for 2 years after the index date. Excluded subjects were those who died during the observation period, had an “unknown” study variable, or whose primary care physician or clinic/hospital could not be defined.

The first year of observation was considered the COC period. The number of asthma-related outpatient visits in this period was used to calculate the COC index, which represented the extent of care provided by the primary care physician. Previous studies have cautioned that bias may occur in calculating the COC index if the patient had too few outpatient visits; as a result, we included only patients with at least 3 asthma-related outpatient visits in the COC period.14-17 The second year of observation was the outcome period, used to estimate asthma ED utilization.

The 74,705 new 0- to 17-year-old patients with asthma in 2007 represented an incidence rate of 1.5% of the 5,002,123 children in Taiwan. After excluding patients who died during the observation period (n = 7), those with too few asthma outpatient visits in the COC period (n = 41,572), those with any study variable unknown (n = 834), and those whose primary care physician or clinic/hospital could not be defined (n = 3015), we studied 29,277 children with asthma.

Variable Measurement

Outcome variables.
The outcome variables included a) asthma ED visit or not, and b) the number of asthma ED visits in the outcome period. An asthma ED visit was defined as an ED visit with a primary or secondary diagnosis of asthma. Because the following were unrelated to regular health-seeking behavior, we excluded any ED visit for injuries, poisoning (ICD-9-CM 850-995) or those with supplementary classifications (V-codes), such as chemotherapy.16,17

Continuity of care. The independent variable was continuity of asthma-specific ambulatory care. Jee and Cabana categorized the types of indexes for measuring COC.18 We opted to use a dispersion-type index because it is easy to calculate, is not prone to be affected by the number of visits, and considers all providers. We used the Continuity of Care Index (COCI),19 a dispersion-type index adopted by numerous studies.

The COCI for asthma-specific ambulatory care was calculated by using the number of a patient’s outpatient visits for asthma (primary or secondary diagnosis) at a clinic or hospital during the COC period. The equation is as follows:

N represents the total number of asthma-related outpatient visits, n is the number of asthma-related outpatient visits to a physician, i is a given physician, and M is the number of physicians.

The COCI value ranges from 0 to 1, with higher values representing better COC. We defined the high COC group (42.3% of subjects) as COCI = 1, indicating that all of a patient’s asthma care in the COC period was provided by the same physician. All other subjects were dichotomized by their median of COCI into the medium COC group (COCI = 0.43-0.99) and the low COC group (COCI <0.43).


Patient characteristics included sex, age (0-4, 5-9, or 10-17 years), income status, urbanization level of insurance registry district, and enrollment in the asthma pay-for-performance (P4P) program. Since health status during the COC period may impact the outcome, we used the total number of asthma outpatient visits as a proxy for health status and disease severity,10,12,15,16,20 categorizing subjects into those with low (3-4), medium (5-8), or high (≥9) visits based on the tertile. We also observed whether the patient had asthma ED visits and the total length of stay for asthma-related hospital admissions during the COC period. For providers, we included sex and mean number of asthma outpatient visits in 2007 and 2008 for the primary care physician responsible for the most asthma care for the patient. We also controlled for the place at which the patient most often received care by the primary care physician, sorting them into hospitals (with fewer than 250, 250 to 499, and 500 or more beds) and nonhospital clinics.

Statistical Analyses

All analyses were conducted using SAS version 9.2 (SAS Institute, Cary, North Carolina). Descriptive statistics included percentage, mean, standard deviation, and minimum and maximum of the study variables. The χ2 test and Kruskal-Wallis test were used for bivariate analyses. The significance level was set as 0.05.

In multivariate analysis, an excess of zeroes (ie, no ED visits) may bias the parameter estimation and affect the inference.21 Most previous studies analyzed all patients and did not take into account the influence of having many patients with no asthma ED visit. In this study, 94.39% of subjects had no asthma ED visit during the outcome period; we therefore used hurdle regression, as developed by Mullahy, rather than multiple regression, Poisson regression, or negative binominal regression.22 Hurdle regression uses a 2-part model: the first component was used to model whether the patient had an asthma ED visit or not by logistic regression; in the second component, which focused on the users only, the number of asthma ED visits was modeled using a left-truncated Poisson regression.

The average COCI of our study subjects was 0.68 (± 0.31) and, of all 29,277 subjects, 12,383 (42.30%) were in the high COC group (COCI = 1), 8317 (28.41%) in the medium COC group (COCI = 0.43-0.99), and 8577 (29.30%) in the low COC group (COCI <0.43). The characteristics of all study subjects and of each COC group are presented in Table 1. All characteristics, except sex and income status, were significantly related to continuity of ambulatory asthma care (P <.001).

Table 2 shows asthma ED utilization during the outcome period. Among all subjects, 1641 (5.61%) had at least 1 asthma ED visit, and the mean number of visits for the users was 1.46 (± 0.99). In the high COC group, 3.96% of patients had at least 1 asthma ED visit; the figures were 6.60% of patients in the medium and 7.02% of patients in the low COC groups. The difference was statistically significant (P <.001). For ED users, the average number of asthma ED visits was 1.42 (± 0.89) in the high COC group, 1.44 (± 0.99) in the medium COC group, and 1.53 (± 1.05) in the low COC group; this difference was statistically significant (P <.001).

The results of hurdle regression are presented in Table 3. The first component (binary OR) of the hurdle regression was used to analyze whether continuity of ambulatory asthma care reduced the risk of an asthma-related ED visit. As a crude result, the risks for the medium and the low COC groups were significantly higher than for the high COC group (OR, 1.72; 95% CI, 1.51-1.94; and OR, 1.83; 95% CI, 1.62-2.07, respectively). After controlling for the covariates mentioned above, the adjusted risks of an asthma-related ED visit for the medium and low COC groups were 1.21 (95% CI, 1.06-1.39) and 1.38 (95% CI, 1.21-1.58) times that of the high COC group, respectively.

The second component (count risk ratio [RR]) of hurdle regression was used to analyze whether continuity of ambulatory asthma care affected the number of asthma ED visits for the users only. As a crude result, the number of ED visits of the low COC group was 23% higher than that of the high COC group (95% CI, 1.04-1.45), but the medium and high COC groups did not differ significantly (RR, 1.03; 95% CI, 0.86-1.23). After controlling for covariates, the number of ED visits did not differ significantly between the medium and high COC groups (RR, 0.86; 95% CI, 0.72-1.04) or between the low and high COC groups (RR, 1.00; 95% CI, 0.84-1.19).

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