Alterations in the intestinal microbial flora have been linked with autoimmune diseases. Our objective was to analyse the composition of the faecal microbiome of children with new-onset juvenile idiopathic arthritis (JIA) compared to healthy controls, and to identify specific gut bacteria associated with JIA. Stool samples from patients were taken at the time of diagnosis of JIA. The microbiome profiles of samples of 30 children with JIA (mean age 6.2 years, 22 girls) were analysed with 16S region-based sequencing profiling and compared to the stool samples of healthy controls (n = 27, mean age 5.4 years, 18 girls). The proportion of bacteria belonging to the phylum Firmicutes was significantly lower in children with JIA [21 % (95 % confident interval [CI]: 17-25 %)] compared to controls [33 % (95 % CI: 26-41 %), p = 0.009]. Bacteria belonging to Bacteroidetes were significantly more abundant in JIA [78 % (95 % CI: 74-82 %)] than in control samples [65 % (95 % CI: 57-73 %), p = 0.008]. Shared operational taxonomic units (OTUs) between the groups revealed that genera Actinobacteria and Fusobacteria were present only in JIA patients and Lentisphaerae only in controls. In summary, faecal flora in JIA is characterised by a low level of Firmicutes and an abundance of Bacteroidetes, resembling the aberration reported in type 1 diabetes. We suggest that alterations in the intestinal microbial flora may challenge the mucosal immune system of genetically susceptible subjects predisposing to local proinflammatory cascades, thus contributing to the development of JIA.

We established cut-off values for LDA and MDA. A reliable definition for HDA will require more patients. In the clinical setting, both the cJADAS10 and JADAS10 serve equally well both for research and quality control purposes. In the future, uniform clinical disease activity levels should be established. We also suggest revising and validating the criteria for HDA. Valid and robust cut-off values for disease activity levels can guide both clinicians and researchers and equip them for quality control.

Objectives To redefine criteria for high disease activity (HDA) in JIA, to establish HDA cut-off values for the 10-joint Juvenile Arthritis Disease Activity Score (JADAS10) and clinical JADAS10 (cJADAS10) and to describe the distribution of patients’ disease activity levels based on the JADAS cut-off values in the literature. Methods Data on 305 treatment-naïve JIA patients were collected from nine paediatric units treating JIA. The median parameters of the JADAS were proposed to be the clinical criteria for HDA. The cut-off values were assessed by using two receiver operating characteristics curve–based methods. The patients were divided into disease activity levels based on currently used JADAS cut-off values. Results We proposed new criteria for HDA. At least three of the following criteria must be satisfied in both disease courses: in oligoarthritis, two or more active joints, ESR above normal, physician global assessment (PGA) of disease activity ≥2 and parent/patient global assessment (PtGA) of well-being ≥2; in polyarthritis, six or more active joints, ESR above normal, PGA of overall disease activity ≥4 and PtGA of well-being ≥2. The HDA cut-off values for JADAS10 (cJADAS) were ≥6.7 (6.7) for oligoarticular and ≥15.3 (14.1) for polyarticular disease. The distribution of the disease activity levels based on the JADAS cut-off values in the literature varied markedly based on which cut-offs were used. Conclusion New clinically derived criteria for HDA in JIA and both JADAS and cJADAS cut-off values for HDA were proposed.