BackgroundIn this nationwide study from the epi-IIRN, we aimed to describe the incidence of very early-onset inflammatory bowel diseases (VEOIBD) with a focus on infantile-onset disease and to compare management and disease course with older children.MethodsData were retrieved from the four Israeli Health-Maintenance-Organizations covering 98% of the population. Pediatric-onset IBD was categorized as: adolescent-onset (10-<18 years), early-onset (6-<10 years), VEOIBD (0-<6 years), toddler-onset (2-<6 years), and infantile-onset (<2 years).ResultsA total of 5,243 children with 35,469 person-years of follow-up were diagnosed with IBD during 2005-2020: 4,444 (85%) adolescent-onset, 548 (10%) early-onset, and 251 (4.8%) VEOIBD, of whom 81 (1.5%) infantile-onset. The incidence of pediatric-onset IBD increased from 10.8/100,000 in 2005 to 15.3/100,000 in 2019 (average annual percent change [AAPC] 2.8% [95%CI 2.2%-3.4%]), but that of VEOIBD remained stable (AAPC 0% [95%CI -2.5%-2.6%]). The infantile-onset and toddler-onset groups were treated less often with biologics (36% and 35%, respectively) vs early-onset (57%) and adolescent-onset (53%; p<0.001). Time to steroid-dependency was shorter in infantile-onset (HR 2.1 [95%CI 1.5-2.9]) and toddler-onset disease (HR 1.6 [95%CI 1.2-2.0]) vs. early-onset and adolescent-onset, but time to hospitalizations, time to surgery and growth delay were worse only in infantile-onset disease. In a multivariable model, infantile-onset patients had higher risk for surgery (HR 1.4 [95%CI 1.1-1.9]) and hospitalization (HR 1.7 [95%CI 1.2-2.4]) than the toddler-onset group.ConclusionThe incidence of VEOIBD remained stable. Infantile-onset IBD had worse outcomes than older children while the toddler-onset had mostly similar outcomes, despite less frequent use of biologics.