Rapid growth in autism spectrum disorder referrals reshaped rehabilitation service use: A longitudinal cohort study of children and adolescents in Brazil

Background The global increase in autism spectrum disorder (ASD) diagnoses is expected to substantially increase demand for long-term rehabilitation services. However, little is known about how this increase affects rehabilitation service utilization and capacity in low- and middle-income countries. Methods We conducted a retrospective longitudinal study of children receiving developmental care at a tertiary rehabilitation center in Salvador, Brazil (2017-2026). Patients were classified into Childhood Autism, Other ASD, and non-ASD diagnostic groups according to ICD-10 diagnoses. Temporal trends in admissions and patients under follow-up were analyzed using generalized additive models and segmented Poisson regression. Factors associated with follow-up duration were evaluated using multivariable Cox proportional hazards models. Results Among 2,123 eligible children, 833 (39.2%) had Childhood Autism, 462 (21.8%) had Other ASD, and 828 (39.0%) had non-ASD diagnoses. Compared with children with non-ASD diagnoses, those with Childhood Autism entered care at younger ages, were predominantly male (77.9% vs. 57.2%), attended more visits, and remained under follow-up longer (all P<0.001). Admissions of children with Childhood Autism increased by 30.2% annually before 2023 but declined thereafter (-19.6% annually; P<0.001). Despite this decline, the number of children with Childhood Autism receiving ongoing rehabilitation continued to increase, reflecting prolonged follow-up. In adjusted analyses, Childhood Autism was associated with a substantially lower hazard of reaching the last recorded follow-up visit than non-ASD diagnoses (adjusted hazard ratio, 0.35; 95% CI, 0.30-0.40; P<0.001). Conclusions The rapid increase in ASD admissions fundamentally reshaped rehabilitation service utilization. Because children with ASD remained under follow-up substantially longer than those with other developmental conditions, they accounted for an increasing share of the rehabilitation caseload, even after new admissions began to decline. These findings highlight the importance of planning rehabilitation services according to both new admissions and the cumulative demand generated by long-term follow-up.