Incidence of idiopathic nephrotic syndrome during the Covid-19 pandemic in the Paris area (France) and in the Netherlands

Abstract

Background The aetiology of idiopathic nephrotic syndrome (INS) remains partially unknown. Viral infections have been associated with INS onset. Since we observed fewer first onset INS cases during the Covid-19 pandemic, we hypothesised that lower INS incidence was the result of lockdown measures. Therefore, the aim of this study was to evaluate the incidence of childhood INS before and during the COVID-19 pandemic in two independent European INS cohorts. Methods Children with new INS in the Netherlands (2018–2021) and Paris area (2018–2021) were included. We estimated incidences using census data for each region. Incidences were compared using two proportion Z-tests. Results A total of 128 and 324 cases of first onset INS were reported in the Netherlands and Paris area, respectively, corresponding to an annual incidence of 1.21 and 2.58 per 100,000 children/year. Boys and young children (< 7 years) were more frequently affected. Incidence before and during the pandemic did not differ. When schools were closed, incidence was lower in both regions: 0.53 vs. 1.31 (p = 0.017) in the Netherlands and 0.94 vs. 2.63 (p = 0.049) in the Paris area. During peaks of hospital admissions for Covid-19, no cases were reported in the Netherlands or Paris area. Conclusions Incidence of INS before and during the Covid-19 pandemic was not different, but when schools were closed during lockdown, incidence was significantly lower. Interestingly, incidences of other respiratory viral infections were also reduced as was air pollution. Together, these results argue for a link between INS onset and viral infections and/or environmental factors. Graphical abstract

Impact of COVID‐19 pandemic on physical health amongst children: Difference‐in‐differences analyses of nationwide school health checkup database

“…[39][40][41][42] Additionally, observational studies reported reductions in the incidence and relapse of the nephrotic and nephritic syndrome amongst children. 43,44 The reasons behind the decrease in glucosuria remain largely unknown; however, changes in adiposity status may not be attributed to this decrease because the incidence rate of diabetes mellitus amongst Japanese children is very low, at 2-3 cases per 100 000 person-years, 45 making it improbable to be reflected in the current data. Alternatively, an increase in the consumption of instant and processed foods during the COVID-19 pandemic might explain the reduction in glucosuria amongst children.…”

“…Consequently, the incidence rates of most infectious diseases (e.g., group A streptococcal pharyngitis) substantially reduced during this period, suggesting decreased incidence of post‐infectious nephritis 39–42 . Additionally, observational studies reported reductions in the incidence and relapse of the nephrotic and nephritic syndrome amongst children 43,44 . The reasons behind the decrease in glucosuria remain largely unknown; however, changes in adiposity status may not be attributed to this decrease because the incidence rate of diabetes mellitus amongst Japanese children is very low, at 2–3 cases per 100 000 person‐years, 45 making it improbable to be reflected in the current data.…”