3.1 Temporal Trends in JIA Prevalence, Incidence, and Mortality
Between 2010-2022, we identified a total 29 758 individuals with JIA up to the age of 16, with incidence ranging between 1381-2394 new JIA cases, per year (details in Table 1). The most common diagnoses were M08.9 (22.3%), M08.8 (20.6%), M08.0 (15.5%), M08.4 (13.6%), M08 (11.7%), M08.3 (4.7%), M08.2 (2.4%), M06 (1.7%), M06.9 (1.2%) and M06.4 (1.2%).
By 2022, the incidence and prevalence rate per 100,000 persons of the GP was calculated as 4.14 and 73.9, respectively. Earlier, between 2010-2015, incidence and prevalance ranged between 6.22-10.3 and 10.4-38.4, respectively. From 2016-2022, both prevalence, but not incidence rates, showed incremental trends with a range of 44.3-69.5 and 3.61-5.94, respectively. For a detailed overview see Figure 1 (raw data in Table 1). Due to stable temporal trends, the mean (95% CI) incidence rate was calculated as 5.65 (4.80-6.50).
Overall, death was a very rare event with only 74 cases recorded in total throughout this time. Annual estimates of the mortality rate ranged from 0 (2010-2012), 0.01 (2013-2014, 2017-2020) to 0.04 (2021-2022) per 100 000 individuals.
With the enhanced population burden of JIA, we investigated potential gender-related differences and identified a stable trend with female predominance (see Figure 2), which corresponds to an average temporal female-to-male incidence ratio of 1.24 (95%CI 1.29-1.18).
3.2 Age Specific JIA Prevalence and Incidence Rates
In order to understand age-specific dynamics in JIA epidemiology, we examined incidence and prevalence rates across age groups (see Figure 3). For prevalence trends, between 2010-2022, incremental rates were observed for patients with ages between 13-18 years. We observed a plateau phase for children aged 2-6 years and and a late plateau for older children 7-12 years of age.
By contrast, incidence rates were similar across age groups, with a modest, generally decremental trend. From an exploratory perspective, we also tracked individuals who previously fulfilled our case definition for JIA (from 2010 and thereafter). Increasing prevalence with very stable incidence rate indicates these individuals of transitional age shift towards other diagnoses. While in absolute counts, or respective to age-specific population size (Figure 3), high prevalence was observed for adults with JIA history, but after considering the adult general population size (ie, true denominator), the annual point prevalence ranged from approximately ~0.3-0.5% in 2022.
Of note, we observed that following transition to adult care, in 2022, most patients were not recorded with inflammatory arthritis (N=10 289, 66.9%), while rheumatoid arthritis (N=3 813, 24.8%), psoriatic arthritis (N=775, 5.0%), ankylosing spondylitis (N=812, 5.3%), Still’s disease (N=78, 0.5%) and inflammatory axial disease (N=430, 2.8%) were the most common transitional patterns.
3.3 Co-morbidity in JIA
For the pediatric JIA population, we examined trends in comorbidity based on healthcare utilization data. In general, pulmonary (N=13 619, 36.4%), ocular (N=12 437, 39.84%), genitourinary (N=6827, 20.0%), neurologic (N=5664, 16.6%), infectious (M=5329, 15.6%), genetic/growth abnormalities (N=5129, 15.0%), ear disorders (N=5013, 14.7%), gastroenterologic (N=4859, 14.2%), neoplasms (N=4730, 13.8%), psychiatric (N=3032, 8.9%), cardiovascular (N=2751, 8.1%) and hematologic (N=1995, 5.8%) disorders, respectively.
We also calculated composite comorbidity scores: the Elixhauser (0 – 9384, 27.5%; 1 – 18 638, 54.5%; 2 – 4 803, 14.1%; 3 – 1 067, 3.1%; 4 – 224, 0.7%) and Charlson score (0 – 25 704, 75.2%; 1- 7 695, 22.5%; 2 – 729, 2.1%; 3- 47, 0.1%) for the whole pediatric JIA population.
For comparative purposes and consistency with the JIA definition, we also examined a restricted population of JIA subjects (pediatric population ≤16 years of age). The most frequent comorbidities were: allergic rhinitis (N=5 200, 17.5%), scoliosis (N=3 844, 12.9%), bronchial asthma (N=3661, 12.3%), chronic tonsillitis/pharyngitis (N=3 641, 12.2%), acne (N=2 879, 9.7%), growth restriction (N=2 311, 7.8%), congenital hip disorder (N=2 304, 7.7%), viral warts (N=2 268, 7.6%), non-purulent middle ear infection (N=2 120, 7.1%), atopic dermatitis (N=2 014, 6.8%), speech disorder (N=1 833, 6.2%), headache syndromes (N=1 703, 5.7%), heart murmur (N=1 651, 5.6%), reactive arthropathy (N=1646, 5.5%), chorioretinal disorders (N=992, 3.3%) and chronic sinusitis (N=990, 3.3%).
3.4 Direct cost of JIA
Over 214 285 visits, we calculated healthcare costs of JIA treatment based on claims from public care visits with corresponding primary reimbursement claims, which amount to an annual median (IQR, range) cost of 37.8€ (47.4-11.6€, 30.3-86.1€, respectively) per patient. Between 2010-2022, the total cost of JIA treatment amounts to over 3 540 000€, with a median (IQR, range) JIA cost of 232 000€ (178 000-309 000€, 103 000-573 000€, respectively) per year (Figure 4). The median (IQR, range) cost per visit was 14.1€ (12.1-18.3€, 9.70-33.8€), respectively.