ObjectivesResearch on spatial variability of the incidence of IgA vasculitis (IgAV) in children and its potential implications for elucidation of the multifactorial aetiology and pathogenesis is limited. We intended to observe spatial variability of the incidence of IgAV and IgA vasculitis-associated nephritis (IgAVN) using modern geostatistical methods, and hypothesised that their spatial distribution may be spatially clustered.MethodsPatients' data were retrospectively collected from 2009 to 2019 in five Croatian University Hospital Centres for paediatric rheumatology, and census data were used to calculate the incidence of IgAV. Using spatial empirical Bayesian smoothing, local Morans’ I and local indicator of spatial autocorrelation (LISA), we performed spatial statistical analysis.Results596 children diagnosed with IgAV were included in this study, of which 313 (52.52%) were male. The average annual incidence proportion was estimated to be 6.79 per 100 000 children, and the prevalence of IgAVN was 19.6%. Existence of spatial autocorrelation was observed in both IgAV and IgAVN; however, clustering distribution differed. While IgAV showed clustering in Mediterranean and west continental part around cities, IgAVN was clustered in the northern Mediterranean and eastern continental part, where a linear cluster following the Drava and Danube river was observed.ConclusionIgAV incidence in Croatia is similar to other European countries. Spatial statistical analysis showed a non-random distribution of IgAV and IgAVN. Although aetiological associations cannot be inferred, spatial analytical techniques may help in investigating and generating new hypotheses in non-communicable diseases considering possible environmental risk factors and identification of potential genetic or epigenetic diversity.

<b><i>Background/Objective:</i></b> The purpose of this study was to evaluate the prevalence and severity of skin involvement in children with IgA vasculitis (IgAV) and its relationship with clinical and biochemical parameters and the risk of developing IgA vasculitis nephritis (IgAVN), the only cause of long-term morbidity and the main prognostic factor in IgAV patients. <b><i>Methods:</i></b> This national multicenter retrospective study included 611 patients under the age of 18 years with IgAV referred to five Croatian tertiary hospitals between 2009 and 2019. Patient data were collected from a database with systematic analysis of IgAV patients in the Croatian population. <b><i>Results:</i></b> Among the 611 children, 205 (33.55%) had purpura on the lower extremities, in 207 (33.88%) the rash extended on the trunk, in 149 (24.39%) it extended to the upper extremities, in 32 (5.24%) the rash was generalized, while 15 (2.47%) had the most severe skin symptoms: bullae, ulcerations, and necroses. IgAVN developed in 130 (21.28%) and persistent IgAVN (present for &#x3e;3 months) in 48 (7.86%) children. Multivariate logistic regression found that presence of ulcerations and necroses (OR 3.20 [95% CI 1.03–9.91]), persistent purpura (OR 2.89 [95% CI 1.71–4.88]), and higher age (OR 1.16 [95% CI 1.09–1.23]) were significant predictors of IgAVN, whereas persistent purpura (OR 20.11 [95% CI 1.09–372.52]), male sex (OR 3.32 [95% CI 1.13–9.80]), and higher age (OR 1.15 [95% CI 1.00–1.30]) were predictors of persistent IgAVN. Among the laboratory parameters, higher serum urea (OR 1.43 [95% CI 1.03–2.00]) and reduction in activated partial thromboplastin time (OR 0.83 [95% CI 0.74–0.93]) were shown to have a significant impact on increasing the risk of persistent IgAVN. <b><i>Conclusion:</i></b> With increasing severity and duration of cutaneous manifestations in IgAV, the risk of developing IgAVN increases, making the prognosis worse, with a greater likelihood to need more aggressive treatment.

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