Objectives Research 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.
Methods Patients' 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.
Results 596 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.
Conclusion IgAV 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.
- systemic vasculitis
- autoimmune diseases
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Handling editor Josef S Smolen
Contributors MSa and MJ designed the research and prepared and analysed the data. MJ is the project Leader of Croatian Science Foundation Research Project IP-2019-04-8822: 'Histological, Clinical, Laboratory and Genetic Predictors of Outcome in Patients with Henoch-Schönlein Purpura and Nephritis (PURPURAPREDICTORS)'; she reviewed and revised the manuscript and supervised the research. MSa wrote the first draft, interpreted the results, reviewed the literature and revised the draft. MF, MSe, SS, AO, MBV and AG contributed to the acquisition and interpretation of data for the study: they examined the patients, performed rheumatological assessments, created a database which includes patients with IgAV and contributed in interpreting the study data and in writing the manuscript. KK, DB and KM contributed to the analysis and interpretation of data for the study: they performed the statistics, developed the figures, analysed and interpreted the study data and contributed in writing the manuscript. All authors read and approved the final manuscript to be published. All coauthors are fully responsible for all aspects of the study and the final manuscript. All authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Funding This work has been fully supported by Croatian Science Foundation under the project IP-2019-04-8822.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Patient consent for publication Not required.
Ethics approval The study was approved by the ethics committee of the University of Zagreb School of Medicine, Zagreb, Croatia (date: 18 September 2019; protocol number - Class: 641-01/19-02/01).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. The data that support the findings of this study are available upon request from the corresponding author.
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