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Target trial emulation (TTE) applies the principles of randomized controlled trials to the causal analysis of observational data sets. One challenge that is rarely considered in TTE is the sources of bias that may arise if the variables involved in the definition of eligibility for the trial are missing. We highlight patterns of bias that might arise when estimating the causal effect of a point exposure when restricting the target trial to individuals with complete eligibility data. Simulations consider realistic scenarios where the variables affecting eligibility modify the causal effect of the exposure and are missing at random or missing not at random. We discuss means to address these patterns of bias, namely: 1) controlling for the collider bias induced by the missing data on eligibility, and 2) imputing the missing values of the eligibility variables prior to selection into the target trial. Results are compared with the results when TTE is performed ignoring the impact of missing eligibility. A study of palivizumab, a monoclonal antibody recommended for the prevention of respiratory hospital admissions due to respiratory syncytial virus in high-risk infants, is used for illustration.

ObjectiveTo determine the birth prevalence, maternal risk factors and 5-year survival for isolated and complex anorectal malformations.DesignNational birth cohort using hospital admission data and death records.SettingAll National Health Service England hospitals.PatientsLive-born singletons delivered from 2002 through 2018, with evidence in the first year of life of a diagnosis of an anorectal malformation and repair during a hospital admission, or anorectal malformation recorded on the death certificate. Cases were further classified as isolated or complex depending on the presence of additional anomalies.Main outcome measuresBirth prevalence of anorectal malformations per 10 000 live births, risk ratios for isolated and complex anorectal malformation by maternal, infant and birth characteristics, and 5-year survival.ResultsWe identified 3325 infants with anorectal malformations among 9 474 147 live-born singletons; 61.7% (n=2050) of cases were complex. Birth prevalence was 3.5 per 10 000 live births (95% CI 3.4 to 3.6). Complex anorectal malformations were associated with maternal age extremes after accounting for other sociodemographic factors. Compared with maternal ages 25–34 years, the risk of complex anorectal malformations was 31% higher for ≥35 years (95% CI 17 to 48) and 13% higher for ≤24 years (95% CI 0 to 27). Among 2376 anorectal malformation cases (n=1450 complex) born from 2002 through 2014, 5-year survival was lower for complex (86.9%; 95% CI 85.1% to 88.5%) than isolated anorectal malformations (98.2%; 95% CI 97.1% to 98.9%). Preterm infants with complex anorectal malformations had the lowest survival (73.4%; 95% CI 68.1% to 78.0%).ConclusionsDifferences in maternal risk factors for isolated and complex anorectal malformations may reflect different underlying mechanisms for occurrence. Five-year survival is high but lowest for preterm children with complex anorectal malformations.

ObjectivesPalivizumab is a monoclonal antibody which can prevent infection with respiratory syncytial virus (RSV). Due to its high cost, it is recommended for high-risk infants only. We aimed to determine the proportion of infants eligible for palivizumab treatment in England who receive at least one dose.MethodsWe used the Hospital Treatment Insights database containing hospital admission records linked to hospital pharmacy dispensing data for 43/153 hospitals in England. Infants born between 2010 and 2016 were considered eligible for palivizumab if their medical records indicated chronic lung disease (CLD), congenital heart disease (CHD), or severe immunodeficiency (SCID), and they met additional criteria based on gestational age at birth and age at start of the RSV season (beginning of October). We calculated the proportion of infants who received at least one dose of palivizumab in their first RSV season, and modelled the odds of treatment according to multiple child characteristics using logistic regression models.ResultsWe identified 3,712 eligible children, of whom 2,479 (67%) had complete information on all risk factors. Palivizumab was prescribed to 832 of eligible children (34%). Being born at ConclusionIn England, palivizumab is not prescribed to the majority of children who are eligible to receive it. Doctors managing these infants might be unfamiliar with the eligibility criteria or are constrained by other considerations, such as cost.

BACKGROUND: Population-based administrative data have rarely been used to compare the birth prevalence, risk factors for occurrence, and mortality of congenital diaphragmatic hernia (CDH) subtypes. OBJECTIVES: We used a national birth cohort to identify CDH subtypes and compared their birth prevalence, relationship with maternal age after accounting for sociodemographic factors, and 1-year mortality rates. METHODS: Linked hospital admission and death records were used to identify isolated and complex CDH cases (involving additional anomalies) among singleton livebirths in England between 2002 and 2018. The prevalence of each CDH subtype per 10,000 livebirths was estimated overall and by infant, birth and maternal characteristics. The relationship between maternal age and each subtype relative to no CDH was examined using multivariable log-binomial regression to estimate risk ratios (RRs). One-year mortality rates were examined using Kaplan-Meier curves and the hazard ratio (HR) of complex versus isolated CDH was calculated using Cox regression. RESULTS: Among 9.5 million livebirths, we identified 1285 with isolated CDH and 1150 with complex CDH. The overall prevalence of isolated and complex CDH was 1.4 (95% confidence interval [CI] 1.3, 1.4) and 1.2 (95% CI 1.1, 1.3) per 10,000 livebirths, respectively. Only complex CDH was associated with maternal age. Compared with maternal age 25-34 years, complex CDH risk was elevated for maternal age

BackgroundAntibiotic prescribing during childhood, most commonly for respiratory tract infections (RTIs), contributes to antimicrobial resistance, which is a major public health concern.AimTo identify factors associated with amoxicillin prescribing and RTI consultation attendance in young children in primary care.Design and settingCohort study in Bradford spanning pregnancy to age 24 months, collected 2007–2013, linked to electronic primary care and air pollution data.MethodAmoxicillin prescribing and RTI consultation rates/1000 child–years were calculated. Mixed-effects logistic regression models were fitted with general practice (GP) surgery as the random effect.ResultsThe amoxicillin prescribing rate among 2493 children was 710/1000 child–years during year 1 (95% confidence interval [CI] = 677 to 744) and 780/1000 (95% CI = 745 to 816) during year 2. During year 1, odds of amoxicillin prescribing were higher for boys (adjusted odds ratio [aOR] 1.36, 95% CI = 1.14 to 1.61), infants from socioeconomically deprived households (aOR 1.36, 95% CI = 1.00 to 1.86), and infants with a Pakistani ethnic background (with mothers born in the UK [aOR 1.44, 95% CI = 1.06 to 1.94] and outside [aOR 1.42, 95% CI = 1.07 to 1.90]). During year 2, odds of amoxicillin prescribing were higher for infants with a Pakistani ethnic background (with mothers born in the UK [aOR 1.46, 95% CI = 1.10 to 1.94] and outside [aOR 1.56, 95% CI = 1.19 to 2.04]) and those born ConclusionSocioeconomic status and ethnic background were associated with amoxicillin prescribing during childhood. Efforts to reduce RTI spread in household and childcare settings may reduce antibiotic prescribing in primary care.

Background Congenital anomalies are a major cause of co‐morbidity in children. Diagnostic code lists are increasingly used to identify congenital anomalies in administrative health records. Evidence is lacking on comparability of these code lists. Objectives To compare prevalence of congenital anomalies and prognostic outcomes for children with congenital anomalies identified in administrative health records using three different code lists. Methods We developed national cohorts of singleton livebirths in England (n = 7 354 363, 2003‐2014) and Scotland (n = 493 556, 2003‐2011). Children with congenital anomalies were identified if congenital anomaly diagnosis was recorded at birth, during subsequent hospital admission or as cause of death before 2 years old. We used three code lists: the EUROCAT list for congenital anomaly surveillance in Europe; the Hardelid list developed to identify children with chronic conditions (including congenital anomalies) admitted to hospital in England; and the Feudtner list developed to indicate children with complex chronic conditions (including congenital anomalies) admitted to hospitals in the United States. We compared prevalence, and risks of postnatal hospital readmission and death according to each code list in England and Scotland. Results Prevalence of congenital anomalies was highest using the EUROCAT list (4.1% of livebirths in England, 3.7% in Scotland), followed by Hardelid (3.1% and 3.0% of livebirths, respectively) and Feudtner (1.8% and 1.5% of livebirths, respectively). 67.2%‐73.3% of children with congenital anomalies in England and 65.2%‐77.0% in Scotland had at least one postnatal hospital admission across the three code lists; mortality ranged between 42.6‐75.4 and 41.5‐88.7 deaths per 1000 births in England Scotland, respectively. The risk of these adverse outcomes was highest using Feudtner and lowest using EUROCAT code lists. Conclusions The prevalence of congenital anomalies varied by congenital anomaly code list, over time and between countries, reflecting in part differences in hospital coding practices and admission thresholds. As a minimum, researchers using administrative health data to study congenital anomalies should report sensitivity analyses using different code lists.

Background There is limited understanding of the drivers of increasing infant accident and emergency (A&E) attendances and emergency hospital admissions across England. We examine variations in use of emergency hospital services among infants by local areas in England and investigate the extent to which infant and socio-economic factors explain these variations. Methods Birth cohort study using linked administrative Hospital Episode Statistics data in England. Singleton live births between 1-April-2012 and 31-March-2019 were followed up for 1 year; from 1-April-2013 (from the discharge date of their birth admission) until their first birthday, death or 31-March-2019. Mixed effects negative binomial models were used to calculate incidence rate ratios for A&E attendances and emergency admissions and mixed effects logistic regression models estimated odds ratio of conversion (the proportion of infants subsequently admitted after attending A&E). Models were adjusted for individual-level factors and included a random effect for local authority (LA). Results The cohort comprised 3,665,414 births in 150 English LAs. Rates of A&E attendances and emergency admissions were highest amongst: infants born Conclusions Drivers of A&E attendances and emergency admissions include individual-level factors such being born premature, with congenital anomaly and from socio-economically disadvantaged young parent families. Support for such vulnerable infants and families should be provided alongside preventative health care in primary and community care settings. The impact of these services requires further investigation. Substantial geographical variations in rates were not explained by individual-level factors. This suggests more detailed understanding of local and underlying service-level factors would provide targets for further research on mechanisms and policy priority.

ObjectiveTo compare mortality in children aged DesignBirth cohort study using linked administrative health databases from England and Sweden.Setting and participantsSingleton live births between 2003 and 2012 in England and Sweden, followed up from age 31 days until the fifth birthday, death or 31 December 2013.Main outcome measuresThe main outcome measures were HR for RTI-related mortality at 31–364 days and at 1–4 years and SUDI mortality at 31–364 days in England versus Sweden estimated using Cox proportional hazards models. We calculated unadjusted HRs and HRs adjusted for birth characteristics (gestational age, birth weight, sex and congenital anomalies) and socioeconomic factors (maternal age and socioeconomic status).ResultsThe English cohort comprised 3 928 483 births, 768 RTI-related deaths at 31–364 days, 691 RTI-related deaths at 1–4 years and 1166 SUDIs; the corresponding figures for the Swedish cohort were 1 012 682, 131, 118 and 189. At 31–364 days, unadjusted HR for RTI-related death in England versus Sweden was 1.52 (95% CI 1.26 to 1.82). After adjusting for birth characteristics, the HR reduced to 1.16 (95% CI 0.96 to 1.40) and for socioeconomic factors to 1.11 (95% CI 0.92 to 1.34). At 1–4 years, unadjusted HR was 1.58 (95% CI 1.30 to 1.92) and decreased to 1.32 (95% CI 1.09 to 1.61) after adjusting for birth characteristics and to 1.30 (95% CI 1.07 to 1.59) after further adjustment for socioeconomic factors. For SUDI, the respective HRs were 1.59 (95% CI 1.36 to 1.85) in the unadjusted model, and 1.40 (95% CI 1.20 to 1.63) after accounting for birth characteristics and 1.19 (95% CI 1.02 to 1.39) in the fully adjusted model.ConclusionInterventions that improve maternal health before and during pregnancy to reduce the prevalence of adverse birth characteristics and address poverty could reduce child mortality due to RTIs and SUDIs in England.

Background Bronchiolitis caused by respiratory syncytial virus (RSV) is a major cause of mortality and morbidity in infants. Aim To describe RSV epidemiology in children in the community in a high-income setting. Methods We used stored blood samples from the United Kingdom Born in Bradford cohort study that had been collected at birth, age 1 and 2 years old, tested for IgG RSV postfusion F antibody and linked to questionnaires and primary and hospital care records. We used finite mixture models to classify children as RSV infected/not infected according to their antibody concentrations at age 1 and 2 years. We assessed risk factors for primary RSV infection at each age using Poisson regression models. Results The study cohort included 700 children with cord blood samples; 490 had additional blood samples taken at both ages 1 and 2 years old. Of these 490 children, 258 (53%; 95% confidence interval (CI): 48–57%) were first infected with RSV at age 1, 99 of whom (38%; 95% CI: 33–43%) had been in contact with healthcare during peak RSV season (November–January). Having older siblings, birth in October–June and attending formal childcare were associated with risk of RSV infection in infancy. By age 2, a further 164 of 490 children (33%; 95% CI: 29–38%) had been infected. Conclusion Over half of children experienced RSV infection in infancy, a further one third had evidence of primary RSV infection by age 2, and one in seven remained seronegative by their second birthday. These findings will inform future analyses to assess the cost-effectiveness of RSV vaccination programmes in high-income settings.

Background National birth cohorts derived from administrative health databases constitute unique resources for child health research due to whole country coverage, ongoing follow-up and linkage to other data sources. In England, a national birth cohort can be developed using Hospital Episode Statistics (HES), an administrative database covering details of all publicly funded hospital activity, including 97% of births, with longitudinal follow-up via linkage to hospital and mortality records. We present methods for developing a national birth cohort using HES and assess the impact of changes to data collection over time on coverage and completeness of linked follow-up records for children. Methods We developed a national cohort of singleton live births in 1998–2015, with information on key risk factors at birth (birth weight, gestational age, maternal age, ethnicity, area-level deprivation). We identified three changes to data collection, which could affect linkage of births to follow-up records: (1) the introduction of the “NHS Numbers for Babies (NN4B)”, an on-line system which enabled maternity staff to request a unique healthcare patient identifier (NHS number) immediately at birth rather than at civil registration, in Q4 2002; (2) the introduction of additional data quality checks at civil registration in Q3 2009; and (3) correcting a postcode extraction error for births by the data provider in Q2 2013. We evaluated the impact of these changes on trends in two outcomes in infancy: hospital readmissions after birth (using interrupted time series analyses) and mortality rates (compared to published national statistics). Results The cohort covered 10,653,998 babies, accounting for 96% of singleton live births in England in 1998–2015. Overall, 2,077,929 infants (19.5%) had at least one hospital readmission after birth. Readmission rates declined by 0.2% percentage points per annual quarter in Q1 1998 to Q3 2002, shifted up by 6.1% percentage points (compared to the expected value based on the trend before Q4 2002) to 17.7% in Q4 2002 when NN4B was introduced, and increased by 0.1% percentage points per annual quarter thereafter. Infant mortality rates were under-reported by 16% for births in 1998–2002 and similar to published national mortality statistics for births in 2003–2015. The trends in infant readmission were not affected by changes to data collection practices in Q3 2009 and Q2 2013, but the proportion of unlinked mortality records in HES and in ONS further declined after 2009. Discussion HES can be used to develop a national birth cohort for child health research with follow-up via linkage to hospital and mortality records for children born from 2003 onwards. Re-linking births before 2003 to their follow-up records would maximise potential benefits of this rich resource, enabling studies of outcomes in adolescents with over 20 years of follow-up.

Background Infant mortality has been rising in England since 2014. We examined potential drivers of these trends. Methods We used aggregate data on all live births, stillbirths and linked infant deaths in England in 2006–2016 from the Office for National Statistics. We compared trends in infant mortality rates overall, excluding births at Results Infant mortality decreased from 4.78 deaths/1000 live births in 2006 to 3.54/1000 in 2014 (annual decrease of 0.15/1000) and increased to 3.67/1000 in 2016 (annual increase of 0.07/1000). This rise was driven by increases in deaths at 0–6 days of life. After excluding infants born at Conclusions The observed increase in infant mortality rates since 2014 is wholly explained by an increasing number of deaths at 0–6 days of age among babies born at

The UK has one of the highest child mortality rates in Western Europe: 4 in every 1000 children die before the age of 1 year, compared with 2 per 1000 children in Sweden. Likewise, the mortality rate of children aged 1–14 years in the UK is 10.4/100 000 children compared with 8.3/100 000 in Sweden.1 Since the UK has a universal healthcare system, and comparable levels of per capita incometo Sweden, a substantial proportion of deaths in children in the UK are likely to be preventable. This raises the question of what policies we should prioritise in order to lower child mortality rates in the UK most rapidly. Data on child deaths are crucial to answering this question. In the November 2018 issue of Archives , Garstang,2 in an editorial linked to a paper by Firth et al ,3 argues that a national dataset collated from Child Death Overview Panels (CDOPs) will allow us to ‘ understand better why children die in the UK and reduce our child mortality ’. In this commentary, we compare data collected by CDOPs to mortality data collected via linked civil registration and administrative data systems. We propose that important lessons for preventing child deaths can already be drawn from analyses of mortality records linked to other administrative datasets and at relatively low cost. Targeted use of detailed investigations into the circumstances of child death could be guided by and enhance findings from administrative data, but the priority should be greater use and wider linkage of these data to inform strategies to prevent child deaths. There are approximately 4000 deaths in children less than 18 years old in England every year.4 5 The circumstances of each of these deaths will be reviewed by one of 148 CDOPs. A CDOP has 12 panel members on average, who …

IntroductionChild mortality is nearly twice as high in England as in Sweden. A comparison of mortality from potentially preventable causes could inform health system responses. This study focused on respiratory tract infection (RTI)-related deaths, amenable to healthcare interventions, and sudden unexpected deaths in infancy (SUDI), amenable to public health interventions. Objectives and ApproachWe developed nationally-representative birth cohorts of singleton live births in 2003-2012 using a hospital admissions database in England and the Medical Birth Register in Sweden. Children were followed-up from 31st day of life until their fifth birthday via linkage to hospital admission and mortality records. We compared child mortality using Cox proportional hazards models to estimate hazard ratios (HR) for England versus Sweden for RTI-related mortality at 31-364 days and 1-4 years, and for SUDI mortality at 31-364 days. Models were adjusted for birth characteristics (gestational age, birthweight, sex, congenital anomalies), and socio-economic factors (maternal age and socio-economic status). ResultsOf 3,928,483 children in England, there were 807 RTI-related deaths at 31-364 days (17% of all deaths in the age range), 691 deaths at 1-4 years (31%), and 1,166 SUDIs (24%) in England. Corresponding figures for 1,012,682 children in Sweden were 136 (18%), 118 (25%) and 189 (24%). Unadjusted HRs for RTI-related deaths in England versus Sweden were 1.50 (95% confidence interval: 1.25-1.80) at 31-364 days. Adjustment for birth characteristics reduced the HR to 1.16 (0.97-1.39), and for socio-economic factors to 1.11 (0.92-1.33). Corresponding figures for RTI-related mortality at 1-4 years were 1.58 (1.30-1.92), 1.32 (1.09-1.61) and 1.30 (1.07-1.59), respectively. Unadjusted HRs for SUDIs reduced from 1.59 (1.36-1.85) to 1.40 (1.20-1.63) after adjusting for birth characteristics, and to 1.19 (1.02-1.39) after adjusting for socio-economic factors. Conclusion/ImplicationsHigher prevalence of adverse birth characteristics (such as prematurity, low birthweight, congenital anomalies) contributed to increased risks of RTI-related and SUDI mortality in England relative to Sweden. Therefore, preventive strategies should focus on maternal health and socio-economic circumstances before and during pregnancy to reduce RTI-related and SUDI mortality in England.

Child mortality is almost twice as high in England compared with Sweden. We aimed to establish the extent to which adverse birth characteristics and socioeconomic factors explain this difference.We developed nationally representative cohorts of singleton livebirths between Jan 1, 2003, and Dec 31, 2012, using the Hospital Episode Statistics in England, and the Swedish Medical Birth Register in Sweden, with longitudinal follow-up from linked hospital admissions and mortality records. We analysed mortality as the outcome, based on deaths from any cause at age 2-27 days, 28-364 days, and 1-4 years. We fitted Cox proportional hazard regression models to estimate the hazard ratios (HRs) for England compared with Sweden in all three age groups. The models were adjusted for birth characteristics (gestational age, birthweight, sex, and congenital anomalies), and for socioeconomic factors (maternal age and socioeconomic status).The English cohort comprised 3 932 886 births and 11 392 deaths and the Swedish cohort comprised 1 013 360 births and 1927 deaths. The unadjusted HRs for England compared with Sweden were 1·66 (95% CI 1·53-1·81) at 2-27 days, 1·59 (1·47-1·71) at 28-364 days, and 1·27 (1·15-1·40) at 1-4 years. At 2-27 days, 77% of the excess risk of death in England was explained by birth characteristics and a further 3% by socioeconomic factors. At 28-364 days, 68% of the excess risk of death in England was explained by birth characteristics and a further 11% by socioeconomic factors. At 1-4 years, the adjusted HR did not indicate a significant difference between countries.Excess child mortality in England compared with Sweden was largely explained by the unfavourable distribution of birth characteristics in England. Socioeconomic factors contributed to these differences through associations with adverse birth characteristics and increased mortality after 1 month of age. Policies to reduce child mortality in England could have most impact by reducing adverse birth characteristics through improving the health of women before and during pregnancy and reducing socioeconomic disadvantage.The Farr Institute of Health Informatics Research (through the Medical Research Council, Arthritis Research UK, British Heart Foundation, Cancer Research UK, Chief Scientist Office, Economic and Social Research Council, Engineering and Physical Sciences Research Council, National Institute for Health Research, National Institute for Social Care and Health Research, and the Wellcome Trust).

ObjectivesHigher rates of infant mortality in the UK than in the Nordic countries are partly explained by wider socio-economic disparities in the UK. We examined the extent to which low birth weight mediates the association between socioeconomic status (SES) and infant mortality using causal mediation analysis. We used cohorts of live births identified in administrative hospital data for the whole of Scotland and Denmark to explore the contribution of prenatal factors, represented by low birth weight, to differences in infant mortality between the two countries. ApproachWe included live-born children born in Denmark (n=1,432,205) and Scotland (n=1,427,163) from 1981-2004. Follow up was to 12 months of age. Information on deaths in first year of life was obtained through linkage with cause of death registers. We determined the effect of socioeconomic status on all cause infant mortality by comparing the highest and lowest quintiles of area-based deprivation (based on Carstairs score in Scotland) or level of maternal education in Denmark. Causal mediation analysis was used for survival outcomes with adjustment for maternal age at birth, sex, birth year of the child, and records indicating congenital malformation. ResultsDuring the follow-up, there were 8,158(0.57%) deaths in Denmark and 8,271(0.58%) deaths in Scotland. Comparing with the very high SES group, the overall hazard ratios of death for each SES quintile (starting with the lowest) compared with the highest SES quintile were 1.58(95% Confidence interval: 1.47-1.71), 1.40(1.32-1.49),1.25(1.20-1.30), 1.11(1.09-1.14) in Denmark, and 1.50(1.36-1.65),1.35(1.25-1.45),1.22(1.16-1.28),1.10(1.08-1.13) in Scotland. The proportions of excess infant deaths mediated through low birth weight (starting with the lowest) compared with the highest SES quintile were 54.7%, 52.1%, 49.5%, 46.9% in Denmark, and 26.0%, 23.9%, 22.0%, 20.1% in Scotland. ConclusionOur result suggests that SES has similar effects on infant mortality in Denmark and Scotland but more of the effect of SES on infant mortality is mediated through low birth weight in Denmark. Public health preventive strategies for infant mortality in both countries need to address prenatal risk factors for low birth weight. The substantial direct effects of SES on infant mortality seen in Scotland, which were not mediated through low birth weight, may be explained by other birth characteristics or could reflect persisting SES disparities in the care of infants after birth.

ObjectivesWe aimed to compare prevalence rates of complex congenital anomalies (CCAs) in the first two years of life in England and Scotland using two published CCA diagnosis code lists (phenotypes) developed to identify children who require high levels of healthcare. ApproachWe developed birth cohorts of singleton, hospital live births between 1998-2011 using birth registration, hospitalisation and mortality register datasets from England (n=8,157,213) and from Scotland (n=731,377) from. Children were followed up until 2 years of age. We compared prevalence rates of congenital anomalies using two code lists developed to identify CCAs: a UK chronic condition code list developed by Hardelid et al. and a US medical complexity code list developed by Feudtner et al. Children were classified as having a CCA if a diagnosis code was included in any admission during follow-up as a primary or subsidiary diagnosis. To assess the level of healthcare attention required, we compared the proportion of children who had at least one re-admission to hospital in the first two years of life. ResultsRates of CCAs in England and Scotland were higher using the Hardelid phenotype (2.8% for both countries) than when using the Feudtner phenotype (1.8% in England and 1.5% in Scotland). Rates of CCAs increased in both England and Scotland between 1998 and 2011. The increase was more notable using the Hardelid phenotype (37.2% and 20.2%, in England and Scotland, respectively) compared to the Feudtner phenotype (35.6% and 13.0%). Prevalence rates using the Hardelid phenotype were similar to EUROCAT figures. The proportion of children with at least one re-admission to hospital was higher in the Feudtner code list (69.2% in England and 84.8% in Scotland), than for Hardelid’s code list (67.9% and 72.0% in England and Scotland, respectively). The proportions of children with any of the CCA phenotypes were higher than compared to children without CCAs (24.4% in England and 25.8% in Scotland). ConclusionPrevalence of CCAs and associated hospital use vary depending on choice of CCA code list. Our findings suggest that Feudtner’s code list identifies children with higher level of healthcare needs. The impact of coding methods for defining CCAs in administrative hospital records should be explored and externally validated when comparing prevalence of CCAs and associated hospital use between countries. The impact of coding method for defining CCAs in administrative hospital records should be explored and externally validated when comparing prevalence and admission rates between countries.

Background Bronchiolitis caused by respiratory syncytial virus (RSV) is the most common reason for hospital admissions in infants. The community burden of RSV is less well understood. We used a unique dataset linking serial serological data, questionnaires, and routinely collected health records to undertake the first community-based serological survey of RSV in England. Methods We used stored blood samples, tested for immunoglobulin G RSV postfusion F antibody, linked to questionnaires and primary and secondary care records from the Born in Bradford cohort study, collected at birth, and ages 1 and 2 years. We used finite mixture models to classify children as RSV infected or not infected according to their antibody concentrations. We fitted multivariable Poisson regression models with robust error variances to identify factors associated with increased risk of primary RSV infection at ages younger than 1 year and 1–2 years. Findings The study included 490 children. By their first birthday, 258 children (53%, 95% CI 48–57%) had serological evidence of past RSV infection, 99 (38%) of whom contacted health-care services during peak RSV season (November–January) due to a respiratory tract infection. Having older siblings (adjusted risk ratio [aRR] 1·52, 95% CI 1·21–1·92, comparing one to no older siblings), Pakistani ethnicity (1·31, 1·04–1·65, compared with White British), blood sample taken outside October–December (1·74, 1·35–2·24 for January–March and 1·60, 1·23–2·08 for April–June, compared with October–December), and attending formal childcare (1·40, 1·12–1·75, compared with no formal childcare) were predictive of RSV infection in infancy. A further 164 children (33%, 95% CI 29–38%) were newly infected at ages 1–2 years, 58 (35%) of whom had contact with health-care services. 14% (95% CI 11–17%) had no evidence of RSV infection by age 2 years. Interpretation Around half of children are infected with RSV during the first year of life, and one in seven children remain unexposed after their second year. Our findings will inform future analyses to assess the cost-effectiveness of RSV vaccination programmes. Our novel approach reusing stored blood samples and linked data present a time-efficient and cheap method for future serological surveys of RSV. Funding Wellcome Trust Seed Award In Science (grant reference number 207673/Z/17/Z).

ObjectivesAcute respiratory infections (ARIs) are a global cause of childhood morbidity. We compared temporal trends and socioeconomic disparities for ARI hospitalisations in young children across Western Australia, England and Scotland.DesignRetrospective population-based cohort studies using linked birth, death and hospitalisation data.Setting and participantsPopulation birth cohorts spanning 2000–2012 (Western Australia and Scotland) and 2003–2012 (England).Outcome measuresARI hospitalisations in infants (ResultsThe overall infant ARI admission rate was 44.3/1000 child-years in Western Australia, 40.7/1000 in Scotland and 40.1/1000 in England. Equivalent rates in children aged 1–4 years were 9.0, 7.6 and 7.6. Bronchiolitis was the most common diagnosis. Compared with the least socioeconomically deprived, those most deprived had higher ARI hospitalisation risk (incidence rate ratio 3.9 (95% CI 3.5 to 4.2) for Western Australia; 1.9 (1.7 to 2.1) for England; 1.3 (1.1 to 1.4) for Scotland. ARI admissions in infants were stable in Western Australia but increased annually in England (5%) and Scotland (3%) after adjusting for non-ARI admissions, sex and deprivation.ConclusionsAdmissions for ARI were higher in Western Australia and displayed greater socioeconomic disparities than England and Scotland, where ARI rates are increasing. Prevention programmes focusing on disadvantaged populations in all three countries are likely to translate into real improvements in the burden of ARI in children.