Results and publications

Published online and free to read in Open BMJ, available here: https://bmjopen.bmj.com/content/11/5/e048038 (DOI: http://dx.doi.org/10.1136/bmjopen-2020-048038)

Abstract

Introduction: Respiratory tract infections (RTIs) are the most common reason for hospital admission among children <5 years in the UK. The relative contribution of ambient air pollution exposure and adverse housing conditions to RTI admissions in young children is unclear and has not been assessed in a UK context.

Methods and analysis: The aim of the PICNIC study (Air Pollution, housing and respiratory tract Infections in Children: NatIonal birth Cohort Study) is to quantify the extent to which in-utero, infant and childhood exposures to ambient air pollution and adverse housing conditions are associated with risk of RTI admissions in children <5 years old. We will use national administrative data birth cohorts, including data from all children born in England in 2005–2014 and in Scotland in 1997–2020, created via linkage between civil registration, maternity and hospital admission data sets. We will further enhance these cohorts via linkage to census data on housing conditions and socioeconomic position and small area-level data on ambient air pollution and building characteristics. We will use time-to-event analyses to examine the association between air pollution, housing characteristics and the risk of RTI admissions in children, calculate population attributable fractions for ambient air pollution and housing characteristics, and use causal mediation analyses to explore the mechanisms through which housing and air pollution influence the risk of infant RTI admission.

Ethics, expected impact and dissemination: To date, we have obtained approval from six ethics and information governance committees in England and two in Scotland. Our results will inform parents, national and local governments, the National Health Service and voluntary sector organisations of the relative contribution of adverse housing conditions and air pollution to RTI admissions in young children. We will publish our results in open-access journals and present our results to the public via parent groups and social media and on the PICNIC website. Code and metadata will be published on GitHub.

Published online and free to read in BMJ Paediatrics Open, available here: https://bmjpaedsopen.bmj.com/content/6/1/e001545 (DOI: https://dx.doi.org/10.1136/bmjpo-2022-001545)

Abstract

Background: There have been no population-based studies of SARS-CoV-2 testing, PCR-confirmed infections and COVID-19-related hospital admissions across the full paediatric age range. We examine the epidemiology of SARS-CoV-2 in children and young people (CYP) aged <23 years.

Aim: We used a birth cohort of all children born in Scotland since 1997, constructed via linkage between vital statistics, hospital records and SARS-CoV-2 surveillance data. We calculated risks of tests and PCR-confirmed infections per 1000 CYP-years between August and December 2020, and COVID-19-related hospital admissions per 100 000 CYP-years between February and December 2020. We used Poisson and Cox proportional hazards regression models to determine risk factors.

Results: Among the 1 226 855 CYP in the cohort, there were 378 402 tests (a rate of 770.8/1000 CYP-years (95% CI 768.4 to 773.3)), 19 005 PCR-confirmed infections (179.4/1000 CYP-years (176.9 to 182.0)) and 346 admissions (29.4/100 000 CYP-years (26.3 to 32.8)). Infants had the highest COVID-19-related admission rates. The presence of chronic conditions, particularly multiple types of conditions, was strongly associated with COVID-19-related admissions across all ages. Overall, 49% of admitted CYP had at least one chronic condition recorded.

Conclusions: Infants and CYP with chronic conditions are at highest risk of admission with COVID-19. Half of admitted CYP had chronic conditions. Studies examining COVID-19 vaccine effectiveness among children with chronic conditions and whether maternal vaccine during pregnancy prevents COVID-19 admissions in infants are urgently needed.

Published online and free to read in BMJ Paediatrics Open, available here: https://bmjpaedsopen.bmj.com/content/6/1/e001545 (DOI: https://dx.doi.org/10.1136/bmjpo-2022-001545)

Abstract 

Background: Antibiotic prescribing during childhood contributes to antimicrobial resistance, which is a major public health concern. Antibiotics are most commonly prescribed to children for respiratory tract infections (RTI). 

Aim: To identify factors associated with amoxicillin prescribing and RTI consultation attendance in primary care in young children.

Design and Setting: Cohort study in Bradford with data from pregnancy to age 24-months collected between 2007-2013, linked to electronic primary care and air pollution data. 

Methods: We calculated amoxicillin prescribing rates/1,000 child-years, and fitted mixed-effects logistic regression models, with general practice (GP) surgery as the random effect, to establish risk factors for amoxicillin prescribing and RTI consultation during the first two years. 

Results: Among 2,493 children, the amoxicillin prescribing rate was 710/1,000 child-years during the first year (95% CI: 677-744) and 780/1,000 (745-816) during the second year. Odds of amoxicillin prescribing during year one were higher for infants who were male (adjusted OR 1.4 (1.1-1.6)), socio-economically deprived (1.4 (1.0-1.9)), and with a Pakistani ethnic background (1.4 (1.1-1.9)). Odds of amoxicillin prescribing during the second year were higher for infants with a Pakistani ethnic background (1.5 (1.1-2.0)/1.6 (1.2-2.0)) and pre-/early-term infants (1.2 (1.0-1.5)). Additional risk factors included caesarean delivery, congenital anomalies, household overcrowding, birth season, and formal childcare attendance. GP surgery-level variation explained 7-9% of variation in amoxicillin prescribing. 

Conclusions: Socio-economic status and ethnic background are strongly associated with amoxicillin prescribing and RTI consultations during childhood. Interventions reducing RTI spread in household and childcare settings may reduce antibiotic prescribing in primary care.

Air pollution affects everyone, but young children are particularly vulnerable due to their developing lungs and brains. One of the most harmful pollutants is fine particulate matter (PM₂.₅), which can penetrate deep into the lungs and enter the bloodstream. Exposure to PM₂.₅ has been linked to asthma, impaired lung development, and cardiovascular issues. While air quality in the UK has improved in recent years, little is known about pollution levels in the places where young children spend much of their time — nurseries and preschools.

Our Approach

We analysed air pollution levels around over 21,000 nurseries and childcare providers across England between 2018 and 2022. Using government air quality data from DEFRA and location data for each nursery, we calculated annual average PM₂.₅ concentrations. We also examined how pollution varied by area type (urban vs rural), levels of deprivation, and ethnic composition of local communities.

Key Findings

• Between 2018 and 2022, PM₂.₅ levels fell by approximately 18%.
• Despite this improvement, 96% of nurseries remained above the World Health Organization’s recommended safe limit of 5 µg/m³.
• Nurseries in deprived areas had slightly higher pollution levels than those in more affluent neighbourhoods.
• Higher exposure was also found in urban and ethnically diverse communities compared to rural or majority-white areas.
• The highest pollution levels were recorded in Greater London, Birmingham, and parts of the Midlands and South East.
• Even small increases in PM₂.₅ can have measurable effects on children’s health, including reduced lung growth and increased asthma risk.

Why This Matters

Most young children in England spend many hours each week in nursery settings. Exposure to polluted air during this critical stage of development may have lasting impacts on their health. Improving air quality around childcare facilities is a practical and impactful way to support healthier childhoods.

Next Steps

We recommend targeted measures to reduce traffic emissions near nurseries, expand green spaces, and improve air quality monitoring. Findings will be shared with local authorities and policymakers working on clean-air initiatives.

Funding and Collaboration

This research was supported by Administrative Data Research UK (ESRC/UKRI), Health Data Research UK, the Wellcome Trust, the Natural Environment Research Council (WM-Air), and the NIHR GOSH Biomedical Research Centre.

The study was a collaboration between UCL, Northumbria University, University of Birmingham, UK Health Security Agency, Swansea University, and the London School of Hygiene & Tropical Medicine.

Publication

The full study, “Towards Cleaner Air: PM₂.₅ Exposure and Disparities Around Childcare Providers in England,” is published in Environmental Research (2025).

https://doi.org/10.1016/j.envres.2025.123172