Infants In Norway Research Articles

Variation in antibiotic consumption in very preterm infants-a 10 year population-based study.

Wide variations in antibiotic use in very preterm infants have been reported across centres despite similar rates of infection. We describe 10 year trends in use of antibiotics and regional variations among very preterm infants in Norway. All live-born very preterm infants (<32 weeks gestation) admitted to any neonatal unit in Norway during 2009-18 were included. Main outcomes were antibiotic consumption expressed as days of antibiotic therapy (DOT) per 1000 patient days (PD), regional variations in use across four health regions, rates of sepsis and sepsis-attributable mortality and trends of antibiotic use during the study period. We included 5296 infants: 3646 (69%) were born at 28-31 weeks and 1650 (31%) were born before 28 weeks gestation with similar background characteristics across the four health regions. Overall, 80% of the very preterm infants received antibiotic therapy. The most commonly prescribed antibiotics were the combination of narrow-spectrum β-lactams and aminoglycosides, but between 2009 and 2018 we observed a marked reduction in their use from 100 to 40 DOT per 1000 PD (P < 0.001). In contrast, consumption of broad-spectrum β-lactams remained unchanged (P = 0.308). There were large variations in consumption of vancomycin, broad-spectrum β-lactams and first-generation cephalosporins, but no differences in sepsis-attributable mortality across regions. The overall antibiotic consumption was reduced during the study period. Marked regional variations remained in consumption of broad-spectrum β-lactams and vancomycin, without association to sepsis-attributable mortality. Our results highlight the need for antibiotic stewardship strategies to reduce consumption of antibiotics that may enhance antibiotic resistance development.

Breastfeeding and Sleeping Patterns Among 6–12-Month-Old Infants in Norway

BackgroundParental behavior and infant sleep patterns can vary widely both within and between cultures and settings. Breastfeeding during the second half-year of infancy has been associated with frequent night waking, which is perceived as sleep problem among the Western societies. An understanding of sleeping patterns among breastfed infants during the second half-year of infancy is important in supporting continued breastfeeding.ObjectivesThe study aimed to investigate the sleeping patterns among breastfed infants during second half-year of infancy.MethodsThis is a cross-sectional study. Three hundred and forty-two mothers of 6–12 months old breastfed infants completed the questionnaires on socio-demographic factors, breastfeeding practices, and infant sleeping patterns, which were assessed by using the Brief Infant Sleep Questionnaire (BISQ). The Cox regression model was used to assess the factors that were associated with night sleep duration whereas demographic factors and breastfeeding practices that were associated with night waking frequency were investigated using the Poisson regression model.ResultsOn average, the breastfed infants slept for 11 h during the night and most infants were reported to have night waking (96.8%) and were breastfed at least once at night (93.5%). In the adjusted analyses, infants in the age group 9–12 months were less likely to sleep longer compared to infants in the 6–8 months age group [HR 1.52 95% CI (1.17, 1.98)]. A one-hour increase in daytime sleep and in night wakefulness increased the likelihood of waking up at night by 19% and 24%, respectively. Infants who had been vaccinated within the last 7 days and infants who were breastfed to sleep were more likely to have a shorter nighttime sleep duration. Nighttime breastfeeding frequency was significantly associated with a 17% increase in the likelihood of night waking [IRR 1.17 95% CI (1.13, 1.22)]. Infants who slept on their parents’ bed were 1.28 times more likely to wake up at night compared to infants who slept in a separate room [IRR 1.28 95% CI (1.05, 1.59)]. Infants of parents who reported that their infants’ sleep was not a problem were 34% less likely to wake up compared to infants of parents who reported that their infants’ sleep was a problem [IRR 0.66 95% CI (0.49, 0.87)].Conclusions for PracticeFrequent night waking, bed sharing and night breastfeeding were common among 6–12 months old breastfed infants. Frequent night breastfeeding may lengthen an infant’s nighttime sleep duration. The study findings indicate that adequate information and support should be given to breastfeeding mothers in relation to the sleeping pattern of breastfed infants in order to promote continued breastfeeding practices.

Vitamin B12 and Folate Status in Pregnant Females and Their Infants in Norway: Secondary Analysis from the Mommy’s Food Study

BackgroundVitamin B12 and folate are essential micronutrients important for normal infant growth and development. ObjectivesThe aims were to describe vitamin B12 and folate status in pregnant females and their infants according to commonly used status cutoffs and examine the associations between maternal status, maternal supplement use, and breastfeeding and infant status. MethodsPregnant females were recruited at 18 wk gestation in Bergen, Norway. Maternal vitamin B12 and folate status were measured at gestational weeks 18 (n = 136) and 36 (n = 116), and infant status was measured at ages 3 (n = 73) and 6 (n = 74) mo. ResultsAt gestational weeks 18 and 36, respectively, 4.4% and 2.6% of the mothers had plasma cobalamin concentrations <148 pmol/L, 0.7% and 6.9% had methylmalonic acid (MMA) concentrations >0.26 μmol/L, and 3.7% and 30% had folate concentrations <10 nmol/L. None of the females had total homocysteine (t-Hcy) concentrations >13 μmol/L or 3 combined indicator of vitamin B12 (cB12) < −0.5. At 3 and 6 mo, respectively, 4.1% and 5.4% of the infants had cobalamin concentrations <148 pmol/L, 63% and 74% had t-Hcy concentrations >6.5 μmol/L, 59% and 66% had MMA concentrations >0.26 μmol/L, and 47% and 60% had cB12 > −0.5. None of the infants had folate concentrations <10 nmol/L. Several of the vitamin B12 biomarkers in infants were associated with maternal vitamin B12 status during pregnancy. Breastfed infants had lower vitamin B12 status (as indicated by plasma cobalamin, t-Hcy, and cB12) than nonbreastfed infants at both 3 and 6 mo. Use of supplements during pregnancy was associated with better vitamin B12 status among infants at 3 and 6 mo, as indicated by infants’ cobalamin and t-Hcy concentrations. ConclusionsSubclinical vitamin B12 deficiency among infants was common and associated with maternal vitamin B12 status during pregnancy and breastfeeding. Among the mothers, an increase in biochemical folate deficiency was discovered toward the end of gestation. Further studies are needed to investigate clinical consequences.This trial was registered at clinicaltrials.gov as NCT02610959.

Detection of severe congenital heart defects in live-born infants in Norway 2017-2020.

The aims of this nationwide retrospective cohort study were to determine the time and causes of detection of severe congenital heart defects (CHDs) in live-born infants in Norway between 2017 and 2020. Information regarding live-born infants with severe CHDs was retrieved from national registries and medical records. A total of 219 776 infants were born in Norway from 01.01.2017 to 31.12.2020. Severe CHDs were diagnosed in 442 (0.2%) infants. Of these, 376 (85%) infants were diagnosed either prenatally (n = 203, 46%) or before discharge from hospital after birth (n = 173, 39%). A total of 56 (13%) infants were discharged with undetected CHDs. Time of detection was unknown in 10 cases (2%). The most frequent undetected CHDs at discharge were coarctation of the aorta/aortic arch hypoplasia (n = 24), atrioventricular septal defect (n = 13), anomalous pulmonary venous connection (n = 5) and coronary artery anomalies (n = 4). Seven (13%) children with undetected CHD experienced circulatory collapse out of hospital. Most infants with severe CHDs in Norway were identified prior to hospital discharge. However, some infants were discharged undiagnosed. Awareness of undetected CHDs and immediate cardiac assessment in infants with signs of circulatory failure early in life are still important.

Late-onset sepsis in very preterm infants in Norway in 2009–2018: a population-based study

ObjectiveTo evaluate epidemiology and outcomes among very preterm infants (<32 weeks’ gestation) with culture-positive and culture-negative late-onset sepsis (LOS).DesignCohort study using a nationwide, population-based registry.Setting21 neonatal units in Norway.ParticipantsAll very...

Infant iodine status and associations with maternal iodine nutrition, breast-feeding status and thyroid function.

Adequate iodine nutrition during infancy is required for normal thyroid function and, subsequently, brain development. However, data on infant iodine status in the first year of life are scarce. This study aimed to describe infant iodine status and further explore its associations with maternal iodine nutrition, breast-feeding status and thyroid function. In this cohort study, 113 infants were followed up at ages 3, 6 and 11 months in Norway. Infant and maternal urinary iodine concentration (UIC), maternal iodine intake, breast milk iodine concentration (BMIC), breast-feeding status and infant thyroid function tests were measured. The median infant UIC was 82 µg/l at the age of 3 months and below the WHO cut-off of 100 µg/l. Infant UIC was adequate later in infancy (median 110 µg/l at ages 6 and 11 months). Infant UIC was associated positively with maternal UIC (β = 0·33, 95 % CI (0·12, 0·54)), maternal iodine intake (β = 0·30, 95 % CI (0·18, 0·42)) and BMIC (β = 0·46, 95 % CI (0·13, 0·79)). Breastfed infants had lower median UIC compared with formula-fed infants at ages 3 months (76 v. 190 µg/l) and 6 months (105 v. 315 µg/l). Neither infant UIC nor BMIC were associated with infant thyroid function tests. In conclusion, breastfed infants in Norway are at risk of insufficient iodine intake during the first months of life. Maternal iodine nutrition is important for providing sufficient iodine intake in infants, and awareness of promoting adequate iodine nutrition for lactating women should be prioritised.

Diagnosing atopic dermatitis in the first year of life

Abstract Linked Article: Endre et al. Br J Dermatol 2022; 186:50–58. Atopic dermatitis is a common skin disease, often starting in the first year of life. However, the disease may be difficult to diagnose during infancy, even when using well-defined diagnostic criteria. Atopic dermatitis is also known as atopic eczema. The two terms are often used interchangeably in daily clinical practice, although eczema used alone is usually considered to be a more general term. In children, a diagnosis of atopic dermatitis is thought to mean a worse outcome compared with a diagnosis of eczema. In this study, we report the occurrence of eczema in over 1800 infants in Norway and Sweden at 3, 6 and 12 months of age, and how many of these would fulfil two widely used diagnostic criteria for atopic dermatitis called the UK Working Party criteria and the Hanifin &amp; Rajka’s criteria. Approximately one-third of all the infants had eczema at some point. However, only about one-third of these infants fulfilled either of the two sets of diagnostic criteria for atopic dermatitis. Those who already had eczema at 3 months and those with eczema at more than one visit were most likely to fulfil the criteria. More infants were diagnosed with atopic dermatitis by the Hanifin &amp; Rajka’s criteria than the UK Working Party criteria at 12 months. We found that a diagnosis of atopic dermatitis is hard to confirm in infancy. We recommend repeated examinations and using both sets of diagnostic criteria when diagnosing atopic dermatitis in infants. This approach may be relevant for research studies, but not so much in a busy clinical practice. The term infantile eczema may be more appropriate to use until the characteristics of atopic dermatitis have become clearer after infancy. Linked Article: Endre et al. Br J Dermatol 2022; 186:50–58.

The prevalence and clinical relevance of hyperhomocysteinemia suggesting vitamin B12 deficiency in presumed healthy infants.

Previous studies have demonstrated a high prevalence of biochemical vitamin B12 deficiency in infants in Norway. Increased total homocysteine (tHcy) is the most important marker of B12 deficiency in infants. There is a need to evaluate its clinical relevance. To investigate the prevalence of hyperhomocysteinemia (S-tHcy > 8μmol/L) suggestive of suboptimal B12 status and the prevalence of clinically relevant hyperhomocysteinemia in presumed healthy infants in Norway. Further, to evaluate risk factors, presence of symptoms and psychomotor development in these children. In a prospective study we clinically examined 252 infants aged 3-7 months using standardized neurological and psychomotor tests prior to analyzing biochemical B12 deficiency markers in 250 infants. Twenty-five of 250 (10%) infants had hyperhomocysteinemia combined with clinically relevant symptoms suggestive of B12 deficiency. Hyperhomocysteinemia was associated with tremor, excessive sleep, and sub-normal scores in the fine motor section of the Ages and Stages Questionnaire. One-hundred and fourteen of 250 (46%) infants had hyperhomocysteinemia. Multiple regression analysis showed months of infant formula use as the strongest negative predictor for hyperhomocysteinemia. We have demonstrated associations between symptoms suggestive of infant B12 deficiency and increased levels of tHcy in presumed healthy infants The combination of hyperhomocysteinemia and associated relevant symptoms suggestive of B12 deficiency was a common finding, albeit most infants with hyperhomocysteinemia did not show symptoms.

Early-onset sepsis risk calculator reduces empiric antibiotic use

Kuzniewicz MW, Puopolo KM, Fischer A, Walsh EM, Li S, Newman TB, et al. A Quantitative, Risk-Based Approach to the Management of Neonatal Early-Onset Sepsis. JAMA Pediatr 2017;171:365-71. Question Among newborns, what is the clinical benefit of an early-onset sepsis (EOS) risk calculator, compared with national guidelines, in reducing antibiotic use? Design Cohort. Setting Kaiser Permanente Northern California (KPNC). Participants Neonates, 35 weeks of gestation or older. Intervention EOS calculator or national guidelines. Outcomes Empiric antibiotic use. Main Results Fewer babies in the EOS calculator group experienced blood culture use: adjusted number needed to treat (aNNT) 13 (95% CI, 8 to 42), and less empirical antibiotic administration in the first 24 hours: aNNT, 56 (95% CI, 44 to 77) with no difference between 24 and 72 hours after birth and no clinical outcome differences. Conclusions An EOS calculator reduced neonatal blood culture and empiric antibiotic use. Commentary A liberal threshold for initiating antibiotic therapy in neonates, based on early-onset sepsis (EOS) risk factors with poor predictive value, has led to overuse of antibiotics in non-infected neonates. This contrasts starkly with the low prevalence of EOS. Antibiotic overuse early in life may have severe short-term and long-term adverse consequences.1Esaiassen E. Fjalstad J.W. Juvet L.K. van den Anker J. Klingenberg C. Antibiotic exposure in neonates and early adverse outcomes — a systematic review and meta-analysis.J Antimicrob Chemother. 2017; 72: 1858-1870Crossref PubMed Scopus (83) Google Scholar, 2Bailey L.C. Forrest C.B. Zhang P. Richards T.M. Livshits A. DeRusso P.A. Association of antibiotics in infancy with early childhood obesity.JAMA Pediatr. 2014; 168: 1063-1069Crossref PubMed Scopus (329) Google Scholar This large cohort study from KPNC investigated clinical management of term and near-term infants with suspected or proven EOS over a 6-year period. The remarkable 50% relative reduction in antibiotic use after introduction of an EOS-calculator was not followed by a delay in therapy for infected infants or an increase in readmissions. It is evident that not only the EOS-calculator but also a bundle of co-interventions including improved patient monitoring was implemented, most likely at the same time. Moreover, the KPNC-staff must have undergone rigorous training in order to use the EOS-calculator and follow the bundle of interventions appropriately. The authors are to be congratulated for this very successful approach. The use of an EOS calculator has the potential to reduce antibiotic overuse, especially in areas where maternal risk factors, earlier, may have been over-emphasized. However, similar results may be achieved with different approaches. We recently presented data from a population-based study of 168,000 term infants in Norway over a 3-year period. In our setting, with a tradition of not recommending therapy based on risk factors alone, the proportion of term infants receiving antibiotic therapy in the first week of life was 2.3% and mortality was low.3Fjalstad J.W. Stensvold H.J. Bergseng H. Simonsen G.S. Salvesen B. Rønnestad A. et al.Early onset sepsis and antibiotic exposure in term infants: a nationwide population-based study in Norway.Pediatr Infect Dis J. 2016; 35: 1-6Crossref PubMed Scopus (1) Google Scholar

Twinning in Norway Following the Oslo Massacre: Evidence of a 'Bruce Effect' in Humans.

Emerging theory and empirical work suggest that the 'Bruce Effect', or the increase in spontaneous abortion observed in non-human species when environments become threatening to offspring survival, may also appear in humans. We argue that, if it does, the effect would appear in the odds of twins among male and female live births. We test the hypothesis, implied by our argument, that the odds of a twin among male infants in Norway fell below, while those among females rose above, expected levels among birth cohorts in gestation in July 2011 when a deranged man murdered 77 Norwegians, including many youths. Results support the hypothesis and imply that the Bruce Effect operates in women to autonomically raise the standard of fetal fitness necessary to extend the gestation of twins. This circumstance has implications for using twins to estimate the relative contributions of genes and environment to human responses to exogenous stimuli.

Attitudes and awareness towards weight gain among normal weight and overweight pregnant women

Objectives: (1) To evaluate the proportion who correctly classify- or misclassify maternal weight gain; (2) to investigate weight gain attitudes, and (3) to compare weight gain attitudes with weight gain recommendations by the Institute of Medicine (IOM), as well as background and lifestyle factors.Methods: This is secondary analysis of cohort data collected as part of a prospective study of determinants of macrosomic infants in Norway (the STORKproject). The participants (n = 467) answered a self-administered questionnaire, including report on maternal weight gain and attitudes towards weight gain, in mean gestation week 36.4 (SD = 1.7). The women were also weighted (kg) at the hospital using a digital beam scale.Results: A significant discrepancy was found between self-reported and measured maternal weight gain. About 76% reported to be satisfied with maternal weight gain while 24% were dissatisfied. Women reporting to be dissatisfied were significantly more likely to be sedentary, sick-listed, reporting poor eating habits and to be multiparous.Conclusions: Most women reported to be satisfied with their maternal weight gain, but had gained excessively according to recommended weight gain ranges issued by IOM. Pregnant women may need targeted advice on their specific weight gain and impact of increased weight gain on health variables for mother and child.

Diversity, transmission and persistence of Escherichia coli in a cohort of mothers and their infants

Despite that Escherichia coli is one of the most important bacteria in early infant colonization and immune modulation, we have limited knowledge about diversity, transmission and persistence within human populations for this bacterium. Here we have utilized a novel, growth-independent, direct typing approach to describe E. coli mother-to-child transmission and persistence within infants in a well-defined cohort of 86 mothers and their infants in Norway. Seven gene multilocus sequence typing of 28 study isolates, three probiotic strains, eight Norwegian pathogenic isolates and the ECOR strain collection added a phylogenetic framework to the direct sequencing data. We found that a type B2 subpopulation of the maternal E. coli strains was the main group transmitted to the infants and that the proportion of children carrying their mothers' strain decreased as the children age. Using species richness estimates we also found a limited number of strains within the cohort compared with total E. coli diversity, constraints on infant colonization, and that infant strain diversity levels increased towards maternal diversity levels over time. This knowledge about inheritance and diversity forms a foundation for future understanding of E. coli in human health and disease.

Full-Genome Sequence Analysis of a Multirecombinant Echovirus 3 Strain Isolated from Sewage in Greece

An echovirus 3 (Echo3) strain (strain LR31G7) was isolated from a sewage treatment plant in Greece in 2005. Full-genome molecular, phylogenetic, and SimPlot analyses were conducted in order to reveal the evolutionary pathways of the isolate. Nucleotide and phylogenetic analyses of part of the VP1 genomic region revealed that the isolated strain correlates with Echo3 strains isolated during the same year in France and Japan, implying that the same virus circulated in Europe and Asia. LR31G7 was found to be a recombinant that shares the 3' part of its genome with an Echo25 strain isolated from asymptomatic infants in Norway in 2003. Nucleotide and SimPlot analyses of the VP1-2A junction, where the recombination was located, revealed the exact recombination breakpoint (nucleotides 3357 to 3364). Moreover, there is evidence that recombination events had occurred in 3B-3D region in the evolutionary history of the isolate. Our study indicates that recombination events play major roles in enterovirus evolution and that the circulation of multirecombinant strains with unknown properties could be potentially dangerous for public health.

Molecular and phenotypic characterization of invasive group B streptococcus strains from infants in Norway 2006–2007

Multilocus sequence typing of an almost complete collection of invasive group B streptococcus (GBS) strains from infants in Norway, conducted in 2006–2007, revealed 27 sequence types (ST), of which 23 clustered into five clonal complexes. The case fatality rate of invasive GBS disease in infants was 16/98 (16.3%). Type V strains were predominant among strains resistant to erythromycin and clindamycin (11/18; 61.1%). All type V strains from fatal cases (5/16) were ST1, resistant to erythromycin and clindamycin, and belonged to three pulsed-field gel electrophoresis-clusters. Further analysis of virulence characteristics of these apparently highly virulent subtypes of type V, ST1 GBS strains is warranted.

Pulse oximetry screening as a complementary strategy to detect critical congenital heart defects

To compare strategies with and without first-day of life pulse oximetry screening to detect critical congenital heart defects (CCHDs). Population based study including all live born infants in Norway in 2005 and 2006 (n = 116 057). Postductal (foot) arterial oxygen saturation (SpO(2)) was measured in apparently healthy newborns after transferral to the nursery, with SpO(2) < 95% as cut-off point. Out of 57 959 live births in the hospitals performing pulse oximetry screening, 50 008 (86%) were screened. A total of 136 CCHDs (1.2 per 1000) were diagnosed, 38 (28%) of these prenatally. Of the CCHDs detected after birth, 44/50 (88%) were detected before discharge in the population offered pulse oximetry screening (25 by pulse oximetry), compared to 37/48 (77%) in the non-screened population (p = 0.15). Median times for diagnosing CCHDs in-hospital before discharge were 6 and 16 h after birth respectively (p < 0.0001). In the screened population 6/50 (12%) CCHDs were missed and recognized after discharge because of symptoms. Two of the six missed cases failed the pulse oximetry screening, but were overlooked (echocardiography not performed before discharge). If these cases had been recognized, 4/50 (8%) would have been missed compared to 11/48 (23%) in the non-screened population (p = 0.05). Of the cases missed, 14/17 (82%) had left-sided obstructive lesions. First-day of life pulse oximetry screening provides early in-hospital detection of CCHDs and may reduce the number missed and diagnosed after discharge.

Levels and temporal trends of chlorinated pesticides, polychlorinated biphenyls and brominated flame retardants in individual human breast milk samples from Northern and Southern Norway

Human breast milk samples from primipara women from Northern (Tromsø) ( N = 10) and Southern Norway (Oslo) ( N = 19) collected in 2000–2001 were analysed with respect to hexachlorobenzene (HCB), hexachlorocyclohexane (HCHs), chlordanes (CHLs), DDTs, mirex, toxaphenes (CHBs), polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs) and hexabromocyclododecane (HBCD). CHBs, PBDEs and HBCD were only analysed in the Tromsø samples. Sum-PCBs and sum-DDTs were the major organochlorines (OCs) (170 and 110 ng g −1 lipid weight (lw), respectively). Other OCs were found in levels of approximately 10- to 300-fold lower than sum-PCBs. Overall, the concentrations of OCs followed the decreasing order of PCBs > DDTs > HCB > HCHs ≈ CHLs > CHBs > mirex. Concentrations of sum-HCHs were significantly higher in breast milk from Oslo compared to Tromsø ( p < 0.05). The PCB profile was dominated by PCB-153, -138 and -180. The PBDE pattern was dominated by PBDE-47 and PBDE-153. The median level of sum-PBDEs was 4.1 ng g −1 lw. PBDE-209 was detected in all analysed samples (median 0.13 ng g −1 lw). The estimated daily intake (EDI) for the median (range) of sum mono- ortho (mo) PCBs 8 was 3.7 (1–9) pg TEQ kg −1 body weight per day for breast fed infants in Norway. This exceeded the TDI by a factor of 1.8 (1–4) based only on intake of mono- ortho PCBs. The present study shows that concentrations of OCs in primipara breast milk have decreased 50–60% since 1991, and that this trend is continuing.

Parents' Involvement in Life-and-Death Decisions in Neonatal Intensive Care: Norwegian Attitudes

This article discusses the general view of parents' role in life-and-death decision-making concerning very premature infants in Norway. The article is based on one qualitative study with parents and a survey among Norwegian health personnel. Our findings show that both parents and health-care professionals are ambivalent with regard to the question of who should decide. Parents who have experienced life-and-death discussions concerning their premature infants emphasize that the physician's ability to communicate and to include them as decision-making partners are more important than the parents' right to an autonomous choice. These findings seem to be in line with the official Norwegian recommendations of the subject matter.

Relation between size of delivery unit and neonatal death in low risk deliveries: population based study

AIMTo examine risk of neonatal death after low risk pregnancies in relation to size of delivery units.METHODSA population based study of live born singleton infants in Norway with birthweights of...

Systemic group B streptococcal disease in neonates and young infants in Norway 1985-94.

In the period 1985-94, 237 out of 575,248 (0.41 per 1000) live born infants in Norway were reported to suffer culture-confirmed systemic group B streptococcal disease before their 90th day of life. The annual incidence increased from 0.20 per 1000 live births in 1985 to 0.64 in 1994, due solely to an increase in cases with an onset before the seventh day of life. Future studies should address the possible causes of this increase.

Birth Defects Registered by Double Sampling: A Bayesian Approach Incorporating Covariates and Model Uncertainty

SUMMARY In double-sampling schemes, a large sample is classified by using one method, and a subsample is also classified with a supplementary method. In the application discussed here, we are attempting to identify infants in Norway born with Down's syndrome by using both a national birth registry and a regional registry. Usual methods for analysing such data assume that one classification method is perfect, which is not the case here. We develop a Bayesian approach that allows for error in both registries, includes covariates (here, the age of the mother) and explicitly accounts for our lack of knowledge about the complexity of the relationships between the variables considered. Markov chain Monte Carlo methods are used to approximate the posterior. In the data considered here, the error rates of the two registries appear to be substantial. Despite a strong relationship between maternal age and risk of Down's syndrome, the inclusion of the maternal age covariate does not substantially change the overall estimates.