Time trend and seasonality in medically attended respiratory syncytial virus (RSV) infections in US children aged 0-5 years, January 2010-January 2023

Objective The long-term time trend and seasonality variations of first-time medically attended respiratory syncytial virus(RSV)infections among young children are unknown.We aim to examine the time trend of medically attended first-time RSV infections among young children in the USA from January 2010 through January 2023.Design This is a population-based cohort study using electronic health records(EHRs).Monthly incidence rate of medically attended first-time RSV infection(cases per 10000000 person-days).A time-series regression model was used to model and predict time trends and seasonality.Setting Multicenter and nationwide TriNetX Network in the USA.Participants The study population comprised children aged 0–5 years who had medical visits during the period of January 2010 to January 2023.Results The data included 29013937 medical visits for children aged 0–5 years(46.5%girls and 53.5%boys)from January 2010 through January 2023.From 2010 through 2019,the monthly incidence rate of first-time medically attended RSV infection in children aged 0–5 years followed a consistent seasonal pattern.Seasonal patterns of medically attended RSV infections were significantly disrupted during the COVID-19 pandemic.In 2020,the seasonal variation disappeared with a peak incidence rate of 20 cases per 1000000 person-days,a decrease of 97.4%from the expected peak rate(rate ratio or RR:0.026,95%CI 0.017 to 0.040).In 2021,the seasonality returned but started 4 months earlier,lasted for 9 months,and peaked in August at a rate of 753 cases per 1000000 person-days,a decrease of 9.6%from the expected peak rate(RR:0.90,95%CI 0.82 to 0.99).In 2022,the seasonal pattern is similar to prepandemic years but reached a historically high rate of 2182 cases per 10000000 person-days in November,an increase of 143%from the expected peak rate(RR:2.43,95%CI 2.25 to 2.63).The time trend and seasonality of the EHR-based medically attended RSV infections are consistent with those of RSV-associated hospitalisations from the Centers for Disease Control and Prevention(CDC)survey-based surveillance system.Conclusion The findings show the disrupted seasonality during the COVID-19 pandemic and a historically high surge of paediatric RSV cases that required medical KEY POINTS⇒Question What are the long-term trends and recent seasonality pattern changes in medically attended respiratory syncytial virus(RSV)infections in chil-dren aged 0–5 years in the USA?⇒Findings This population-based cohort study of 29013937 medical visits for children aged 0–5 years found that the monthly incidence rate of first-time medically attended RSV infections followed a consistent seasonal pattern during 2010–2019,the seasonal pattern was significantly disrupted during the COVID-19 pandemic.The seasonal variation dis-appeared in 2020,returned in 2021 but started ear-lier and reached a historical high rate of 2182 cases per 10000000 person-days in November 2022.⇒Meaning These data suggest that COVID-19 pan-demic contributed to the disrupted seasonality and the 2022 surge of paediatric RSV cases that need-ed medical attention.This study demonstrates the potential of electronic health records as a cost-effective alternative for real-time surveillance of un-expected disease patterns including RSV infection.attention in 2022.Our study demonstrates the potential of EHRs as a cost-effective alternative for real-time pathogen and syndromic surveillance of unexpected disease patterns including RSV infection.