Epidemiology of idiopathic nephrotic syndrome in children: endemic or epidemic?

Claire Dossier, Nathanael Lapidus, Florian Bayer, Anne-Laure Sellier-Leclerc, Olivia Boyer, Loic de Pontual, Adrien May, Sylvie Nathanson, Christine Orzechowski, Tabassome Simon, Fabrice Carrat, Georges Deschênes

The etiology of idiopathic nephrotic syndrome (INS) remains partially unknown. Viral infections have been reported to be associated with INS onset and relapse. The aim of this study was to describe the epidemiology of a population-based cohort of children with INS and propose a spatiotemporal analysis. All children aged 6 months to 15 years with INS onset between December 2007 and May 2010 and living in the Paris area were included in a prospective multicenter study. Demographic and clinical features at diagnosis and 2 years were collected. INS was diagnosed in 188 children, 93 % of whom were steroid sensitive. Annual incidence was 3.35/100,000 children. Standardized incidence ratio (SIR) was higher in one of the eight counties: Seine-Saint-Denis, with SIR 1.43 [95 % confidence interval (CI) 1.02-1.95]. A spatial cluster was further identified with higher SIR 1.36 (95 % CI 1.09-1.67). Temporal analysis within this overincidence area showed seasonal variation, with a peak during the winter period (p <0.01). In addition, partition of the Paris area into quintiles of the population showed that the average delay of occurrence, with regard to the first study case, followed a longitudinal progression (p <0.0001). The clustering of cases, the seasonal variation within this particular area, and the progression over the Paris area altogether suggest that INS may occur on an epidemic mode.