Pandemic-Related Reductions in Respiratory Infections and New-Onset Nephrotic Syndrome: A Multicenter Cohort Study in Japan

Rationale & objective Infectious diseases have been associated with pediatric idiopathic nephrotic syndrome (NS). The effect of pandemic-related changes in infection exposure on NS epidemiology remains unclear.Study design Retrospective cohort study.Setting & participants Data from children aged 6 months to 15 years from 11 hospitals in Japan, extracted from the Pediatric Medical Information Collection System. Two periods were compared: prepandemic (April 2019-March 2020) and first pandemic year (April 2020-March 2021).Analytical approach Event counts (new-onset NS, relapse, respiratory tract infections, acetaminophen prescriptions, coronavirus disease 2019 diagnoses) were modeled using a negative binomial generalized linear mixed model with hospital-specific random intercepts. Sensitivity analyses used zero-inflated Poisson, Poisson mixed models, and quasi-Poisson.Results There were 218 new-onset NS cases (127 prepandemic, 91 during the pandemic). The pandemic period was associated with a decrease in incidence, and estimates were similar across distributional sensitivity analyses, whereas extended time-window analyses attenuated statistical significance. The relapse rate among 366 patients in remission was 0.094 per person-year before the pandemic and 0.056 per person-year during the pandemic; the period effect was not statistically significant. Respiratory tract infections decreased by approximately half, and acetaminophen prescriptions declined. The number of coronavirus disease 2019 diagnoses increased sharply.Limitations Observational design limits causal inference. Findings may not generalize beyond Japanese populations.Conclusions Reduced respiratory infection exposure during the pandemic may be associated with lower new-onset NS incidence. Preventive measures against respiratory infections may help reduce NS occurrence.