Of the 43,510 children that enrolled prior to 2 months old, 37,811 (87%) had both an enrollment period that overlapped completely with at least one WCC visit interval and had at least four outpatient claims. Of these children, 867 (2%) children were excluded due to missing geographical location or a location outside of Hawaii. Thus, 36,944 (85%) children, with 35,078 (95%) followed from birth, met the final eligibility requirements ().
Healthy children and children with ≥ one chronic disease comprised 76% (n= 28,023) and 24% (n= 8,921) of the study population, respectively (). Among children with chronic disease, 47% were classified as having asthma (). The top 10 chronic disease diagnoses were present in 84% of children with ≥ one chronic disease.
Top 10 Chronic Disease Classifications
The two groups of children were similar (). However, children with ≥ one chronic disease were in the study longer than healthy children (median 41 vs. 28 months, P<0.001).
WCC Visit Adherence and COC Index
Overall, children were recommended to have a median of 9 WCC visits (Interquartile Range [IQR] 5–10). For 85% of the children, WCC visit adherence was calculated based on at least four recommended WCC visits. A majority of children fell into the highest WCC visit adherence category (). This was similar for healthy children (74%) and children with ≥ one chronic disease (70%).
For COC index calculation, a median of 18 claims was used (IQR 11–26). Compared to healthy children, children with ≥ one chronic disease had 10 more total outpatient claims, visited 1 more different provider, and had 9 more claims by a primary care physician. The majority of children (58%) fell into the highest COC index category (0.75 to 1). However, compared to healthy children, a lower percentage of children with ≥ one chronic disease fell into the highest COC index category (48% vs. 61%, P<0.001; ).
Of the 36,944 children eligible for study inclusion (), 1,396 (4%) had an ACSH. The median age of children with an ACSH was 14 months (IQR 8–23). The proportion of children with an ACSH was 2.7 times greater for children with ≥ one chronic disease compared to healthy children (3% vs. 7%, P<0.001; ).
More than three-quarters of all ACSH were accounted for by the following five conditions: dehydration (24%), acute respiratory tract infections (18%), bacterial pneumonia (17%), seizures (13%), and asthma (12%). While the top five conditions were similar for all children, the most common ACSH condition differed by chronic disease status with asthma being the most common for children with ≥ one chronic disease (20%) and dehydration being the most common for healthy children (28%).
Multivariate, Time-Varying Analyses
The adjusted HR for all children together revealed that both high WCC visit adherence and COC index were associated with decreased risk of an ACSH (). The relationship between WCC visit adherence and risk of ACSH as well as COC index and risk of ACSH differed significantly by chronic disease status (). Our exploratory analysis revealed no statistically significant results when testing for interactions between WCC visit adherence and COC index. The results from the sensitivity analysis using propensity scores to determine whether self-selection bias was occurring were similar to the original model and did not change our conclusions (data not shown).
Adjusted Hazard Ratios for rate of ACSH, Hazard Ratio (95% Confidence Interval)a
For children with ≥ one chronic disease, those in the lowest WCC visit adherence category had nearly 2 times (HR 1.9, 95% CI: 1.5–2.5) the risk of an ACSH compared to those in the highest category. The HR increased as WCC visit adherence decreased (). Similarly, those in the lowest COC index category had 2.4 times (HR 2.4, 95% CI: 1.7–3.5) the risk of an ACSH compared to those in the highest COC index category. The HR also increased as COC index decreased ().
For healthy children, there was no significant association between WCC visit adherence and ACSH. In contrast, similar to children with ≥ one chronic disease, healthy children in the lowest COC index category had nearly 2 times (HR 1.9, 95% CI: 1.2–2.9) the risk of an ACSH compared to those in the highest category. The HR increased as COC index decreased ().