Nearly four in 10 children under 3 who sought care for respiratory symptoms tested positive for RSV in a surveillance study spanning primary, secondary and tertiary care in three English areas. The overall positivity rate was 39.8%. Among children seen in an emergency department, positivity was 36.3% when the visit ended in discharge and 50.0% when the child was admitted.
The primary-care result was lower when all enrolled primary-care presentations were considered: 18.0%. But children with lower respiratory tract infection symptoms in primary care had a positivity rate of 36.5%, while the upper respiratory tract infection substudy recorded 12.7%. Those percentages describe separate groups within the surveillance, so they should not be read as one rate for every child under 3.
The central result is a prevalence estimate, meaning the share of swabs that were positive in each group. It tells us how often RSV was detected among children already presenting for care; it does not measure incidence across every child in England. The difference between the emergency-department groups should therefore be read as an observed association, not a causal result.
A surveillance network across three areas
The surveillance ran from 9 December 2021 to 31 March 2023 in Merseyside, Cheshire and Bristol. It covered 11 primary-care sites, five walk-in centres, two secondary-care hospital sites and two tertiary-care hospital sites. The main surveillance included children with lower respiratory tract infection symptoms, with a separate primary-care upper respiratory tract infection substudy that had a minimum target of 180 participants.
Recruitment produced 2,074 participants. After 74 withdrawals and exclusions, the final analysis included 410 children from primary care and 1,590 from secondary or tertiary care. The upper respiratory substudy included 220 primary-care participants and 98 from walk-in centres.
The planned target was 1,800 participants. The calculation assumed an estimated RSV positivity rate of 0.15 and was designed for 90% power, precision of 0.028 and a 0.05 significance level, using a two-sided exact test.
Each child had a nasal swab on the day of recruitment. Samples were processed at local NHS-associated laboratories using a multiplex panel. Consent was obtained at recruitment or as soon as possible afterward.
The researchers summarized the results with proportions and used chi-squared tests for selected comparisons. They also ran univariate and multivariable logistic regression, statistical methods that estimate associations in terms of odds, and reported odds ratios, confidence intervals and p-values.
The study was registered and had research ethics and Health Research Authority approvals before it began.
A measure of detected infection
Read together, the rates point to a burden that appeared across care levels, not only among children who were admitted. The primary-care overall rate was 18.0%, compared with 36.3% after emergency-department discharge and 50.0% after emergency-department admission. Within primary care, the observed percentages differed by presentation: 36.5% for lower respiratory symptoms versus 12.7% in the upper respiratory substudy.
The percentages come with an important reporting gap: the cited analysis did not provide confidence intervals for them, so the precision of each estimate is not shown. It reported p<0.01 for the comparison between emergency-department admission and discharge. That test addresses a difference in the observed groups; it does not turn the study into a causal test.
The geographical and sampling frame also sets the boundary of the headline number. This was surveillance in Merseyside, Cheshire and Bristol, among children under 3 who presented to participating primary, secondary or tertiary services during the study period. It was not an estimate of RSV incidence or total burden among all children under 3 in England.
The simplest summary is this: among the young children who entered the surveillance, RSV was detected in 39.8% of swabs overall. The proportion varied with where children were seen and how they presented, reaching 50.0% among those admitted from the emergency department. The findings describe the pattern in this sample, rather than proving a cause or forecasting every child's risk.
Paper data and sources
Original title: High respiratory syncytial virus burden in children under 3 years of age across all care levels in England.
Authors: Emma C Carter, Helen Hill, Carla Solórzano et al.
Journal/Repository: BMJ open respiratory research
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1136/bmjresp-2025-003996
Original paper · Full text