Nicolas L. Gilbert

Presence of other allergic disease modifies the effect of early childhood traffic-related air pollution exposure on asthma prevalence

Nitrogen dioxide (NO2), a surrogate measure of traffic-related air pollution (TRAP), has been associated with incident childhood asthma. Timing of exposure and atopic status may be important effect modifiers. We collected cross-sectional data on asthma outcomes from Toronto school children aged 5-9years in 2006. Lifetime home, school and daycare addresses were obtained to derive birth and cumulative NO2 exposures for a nested case-control subset of 1497 children. Presence of other allergic disease (a proxy for atopy) was defined as self-report of one or more of doctor-diagnosed rhinitis, eczema, or food allergy. Generalized estimating equations were used to adjust for potential confounders, and examine hypothesized effect modifiers while accounting for clustering by school. In children with other allergic disease, birth, cumulative and 2006 NO2 were associated with lifetime asthma (OR 1.46, 95% CI 1.08-1.98; 1.37, 95% CI 1.00-1.86; and 1.60, 95% CI 1.09-2.36 respectively per interquartile range increase) and wheeze (OR 1.44, 95% CI 1.10-1.89; 1.31, 95% CI 1.02-1.67; and 1.60, 95% CI 1.16-2.21). No or weaker effects were seen in those without allergic disease, and effect modification was amplified when a more restrictive algorithm was used to define other allergic disease (at least 2 of doctor diagnosed allergic rhinitis, eczema or food allergy). The effects of modest NO2 levels on childhood asthma were modified by the presence of other allergic disease, suggesting a probable role for allergic sensitization in the pathogenesis of TRAP initiated asthma.

Temporal trends in sudden infant death syndrome in Canada from 1991 to 2005: contribution of changes in cause of death assignment practices and in maternal and infant characteristics

Gilbert NL, Fell DB, Joseph KS, Liu S, León JA, Sauve R, for the Fetal and Infant Health Study Group of the Canadian Perinatal Surveillance System. Temporal trends in sudden infant death syndrome in Canada from 1991 to 2005: contribution of changes in cause of death assignment practices and in maternal and infant characteristics. Paediatric and Perinatal Epidemiology 2012; 26: 124–130. The rate of sudden infant death syndrome (SIDS) declined significantly in Canada and the US between the late 1980s and the early 2000s. In the US, this decline was shown to be due in part to a shift in diagnosis, as deaths from accidental suffocation and strangulation in bed and from other ill-defined and unspecified cause increased concurrently. This study was undertaken to determine whether there was such a shift in diagnosis from SIDS to other causes of death in Canada, and to quantify the true temporal decrease in SIDS. Cause-specific infant death rates were compared across three periods: 1991–95, 1996–2000 and 2001–05 using the Canadian linked livebirth-infant death file. The temporal decline in SIDS was estimated after adjustment for maternal and infant characteristics such as maternal age and small-for-gestational age using logistic regression. Deaths from SIDS decreased from 78.4 [95% confidence interval (CI) 73.4, 83.4] per 100 000 livebirths in 1991–95, to 48.5 [95% CI 44.3, 52.7] in 1996–2000 and to 34.6 [95% CI 31.0, 38.3] in 2001–05. Mortality rates from other ill-defined and unspecified causes and accidental suffocation and strangulation in bed remained stable. The temporal decline in SIDS between 1991–95 and 2001–05 did not change substantially after adjustment for maternal and infant factors. It is unlikely that the temporal decline of SIDS in Canada was due to changes in cause-of-death assignment practices or in maternal and infant characteristics.

Differences in perinatal and infant mortality in high-income countries: Artifacts of birth registration or evidence of true differences?

BackgroundVariation in birth registration criteria may compromise international comparisons of fetal and infant mortality. We examined the effect of birth registration practices on fetal and infant mortality rates to determine whether observed differences in perinatal and infant mortality rates were artifacts of birth registration or reflected true differences in health status.MethodsA retrospective population-based cohort study was done using data from Canada, United States, Denmark, Finland, Iceland, Norway, and Sweden from 1995–2005. Main outcome measures included live births by gestational age and birth weight; gestational age—and birth weight-specific stillbirth rates; neonatal, post-neonatal, and cause-specific infant mortality.ResultsProportion of live births <22xa0weeks varied substantially: Sweden (not reported), Iceland (0.00xa0%), Finland (0.001xa0%), Denmark (0.01xa0%), Norway (0.02xa0%), Canada (0.07xa0%) and United States (0.08xa0%). At 22–23 weeks, neonatal mortality rates were highest in Canada (892.2 per 1000 live births), Denmark (879.3) and Iceland (1000.0), moderately high in the United States (724.1), Finland (794.3) and Norway (739.0) and low in Sweden (561.2). Stillbirth:live birth ratios at 22–23 weeks were significantly lower in the United States (79.2 stillbirths per 100 live births) and Finland (90.8) than in Canada (112.1), Iceland (176.2) and Norway (173.9). Crude neonatal mortality rates were 83xa0% higher in Canada and 96xa0% higher in the United States than Finland. Neonatal mortality rates among live births ≥28xa0weeks were lower in Canada and United States compared with Finland. Post-neonatal mortality rates were higher in Canada and United States than in Nordic countries.ConclusionsLive birth frequencies and stillbirth and neonatal mortality patterns at the borderline of viability are likely due to differences in birth registration practices, although true differences in maternal, fetal and infant health cannot be ruled out. This study emphasises the need for further standardisations, in order to enhance the relevance of international comparisons of infant mortality.

Fetuses-at-risk, to avoid paradoxical associations at early gestational ages: extension to preterm infant mortality

BACKGROUNDnFetuses-at-risk denominators are commonly used in research on preterm stillbirth, but applications to postnatal outcomes such as preterm infant mortality are controversial. We evaluated whether biased associations between maternal risk factors and preterm infant mortality caused by stratification by preterm birth could be avoided using fetuses-at-risk risk ratios.nnnMETHODSnData included 3 277 570 births drawn from the linked live birth-death file for Canada from 1990 through 2005. We used maternal age as the risk factor, and estimated the association with stillbirth, early neonatal, late neonatal and postneonatal mortality by gestational interval (22-24, 25-27, 28-31, 32-36, ≥37 weeks). Models were run using (i) log-binomial regression stratified by preterm gestational age, and (ii) unstratified log-binomial regression using fetuses-at-risk denominators.nnnRESULTSnExtremes of maternal age were associated with higher mortality among term births. Among preterm births, the stratified model suggested a protective, null or attenuated association of extremes of maternal age with stillbirth, early, late and post neonatal mortality. The unstratified fetuses-at-risk model, however, resulted in the expected higher risk of mortality at extremes of maternal age for all outcomes.nnnCONCLUSIONSnFetuses-at-risk regression can avoid paradoxical associations between maternal exposures and mortality of infants born early in gestation, caused by preterm birth stratification bias. The fetuses-at-risk approach can be extended through the first year of life, or potentially beyond, depending on the outcome and presence of unmeasured confounders associated with preterm birth.

Smoking Cessation During Pregnancy and Relapse After Childbirth in Canada

OBJECTIVEnThis analysis was undertaken to determine the rates and determinants of smoking cessation during pregnancy and smoking relapse after childbirth in Canada.nnnMETHODSnWe used data from the Maternity Experiences Survey, a cross-sectional study of mothers who gave birth to a singleton baby in Canada in 2006. A total of 1586 mothers who smoked occasionally or daily before pregnancy were included in the analysis.nnnRESULTSnThe rate of smoking cessation during pregnancy was 53.0% (95% CI 50.3% to 55.7%). Higher pre-pregnancy smoking frequency, Inuit origin, being aged ≥ 35 years, lower education, not attending prenatal classes, lack of social support, stress before or during pregnancy, and living with a smoker were independently associated with higher risk of continued smoking, while First Nations (off-reserve) origin was associated with a lower risk. Among those who had quit smoking, 47.1% (95% CI 43.5% to 50.6%) relapsed postpartum. Living with a smoker, not having breastfed, and having stopped breastfeeding were independently associated with a higher risk of relapse.nnnCONCLUSIONnThis study highlights the need to tailor smoking cessation and prevention interventions for some high-risk groups of women.

Estimates and determinants of HPV non-vaccination and vaccine refusal in girls 12 to 14 y of age in Canada: Results from the Childhood National Immunization Coverage Survey, 2013.

ABSTRACT Since the introduction of HPV vaccination programs in Canada in 2007, coverage has been below public health goals in many provinces and territories. This analysis investigated the determinants of HPV non-vaccination and vaccine refusal. Data from the Childhood National Immunization Coverage Survey (CNICS) 2013 were used to estimate the prevalence of HPV non-vaccination and parental vaccine refusal in girls aged 12–14 years, for Canada and the provinces and territories. Multivariate logistic regression was used to examine factors associated with non-vaccination and vaccine refusal, after adjusting for potential confounders. An estimated 27.7% of 12–14 y old girls had not been vaccinated against HPV, and 14.4% of parents reported refusing the vaccine. The magnitude of non-vaccination and vaccine refusal varied by province or territory and also by responding parents country of birth. In addition, higher education was associated with a higher risk of refusal of the HPV vaccine. Rates of HPV non-vaccination and of refusal of the HPV vaccine differ and are influenced by different variables. These findings warrant further investigation.

Temporal Trends in Social Disparities in Maternal Smoking and Breastfeeding in Canada, 1992–2008

A steady decrease in maternal smoking during pregnancy and a steady increase in breastfeeding rates have been observed in Canada in the past two decades. However, the extent to which all socioeconomic classes have benefited from this progress is unknown. Therefore, this study was undertaken to determine: (1) whether progress achieved benefited the entire population or was limited to specific strata; and (2) whether disparities among strata decreased, stayed the same, or increased over time. We used data from the National Longitudinal Survey of Children and Youth, which enrolled children aged 0–3xa0years between 1994 and 2008. Data collected at entry was analyzed in a cross-sectional manner. Between birth years 1992–1996 and 2005–2008, smoking during pregnancy decreased from 11.5xa0% (95xa0% CI 10.0–13.0xa0%) to 5.2xa0% (95xa0% CI 4.1–6.3xa0%) among mothers with a college or university degree and from 43.0xa0% (95xa0% CI 38.8–47.2xa0%) to 38.6xa0% (95xa0% CI 32.9–44.2xa0%) among those with less than secondary education. During the same period, the rate of breastfeeding initiation increased from 83.8xa0% (95xa0% CI 81.9–85.6xa0%) to 91.5xa0% (95xa0% CI 90.2–92.8xa0%) among mothers with a college or university degree and from 63.1xa0% (95xa0% CI 58.9–67.4xa0%) to 74.7xa0% (95xa0% CI 69.8–79.7xa0%) among those with less than secondary education. The risks of smoking and of not breastfeeding remained significantly higher in the least educated category than in the most educated throughout the study period, and these associations remained statistically significant after controlling for maternal age. Gaps between the least and the most educated mothers narrowed for breastfeeding but widened for smoking during pregnancy.

Neighbourhood Income and Neonatal, Postneonatal and Sudden Infant Death Syndrome (SIDS) Mortality in Canada, 1991-2005

BackgroundRates of infant mortality declined in Canada in the 1990s and 2000s, but the extent to which all socio-economic levels benefitted from this progress is unknown.ObjectivesThis study investigated differences and time trends in neonatal, postneonatal and sudden infant death syndrome (SIDS) mortality across neighbourhood income quintiles among live births in Canada from 1991 through 2005.MethodsThe Canadian linked live birth and infant death file was used, excluding births from Ontario, Yukon, Northwest Territories and Nunavut. Mortality rates for neonatal, postneonatal and sudden infant death syndrome (SIDS) were calculated by neighbourhood income quintile and period (1991–1995, 1996–2000, 2001–2005). Hazard ratios (HR) for neighbourhood income quintile and period were computed, adjusting for province of residence, maternal age, parity, infant sex and multiple birth.ResultsIn urban areas, for the entire study period (1991–2005), the poorest neighbourhood income quintile had a higher hazard of neonatal death (adjusted HR 1.24, 95% CI 1.15–1.34), postneonatal death (adjusted HR 1.58, 95% CI 1.41–1.76) and SIDS (adjusted HR 1.83, 95% CI 1.49–2.26) compared to the richest quintile. Postneonatal and SIDS mortality rates declined by 37% and 57%, respectively, between 1991–1995 and 2001–2005 whereas no significant change was observed in neonatal mortality. The decrease in postneonatal and SIDS mortality rates occurred across all income quintiles.ConclusionThis study shows that despite a decrease in infant mortality and SIDS across all neighbourhood income quintiles over time in Canada, socio-economic inequalities persist. This finding highlights the need for effective infant health promotion strategies in vulnerable populations.RésuméContexteLa mortalité infantile a diminué au Canada depuis les années 1990 et 2000 mais nous ignorons si toutes les classes socioéconomiques ont bénéficié également de ce progrès.ObjectifsLa présente étude portait sur les différences entre les taux de mortalité néonatale et postnéonatale et de mort subite du nourrisson entre les différents quintiles de revenu des quartiers au Canada de 1991 à 2005.MéthodesLe fichier couplé des naissances vivantes et des décès infantiles au Canada a été utilisé à l’exclusion des naissances survenues en Ontario, au Yukon, dans les Territoires du Nord-ouest et au Nunavut. Les taux de mortalité néonatale et postnéonatale et de mort subite du nourrisson ont été calculé par quintile de revenu des quartiers et par période (1991–1995, 1996–2000, 2001–2005). Les rapports de risque (RR) ont été calculés par quintile de revenu et période avec ajustement pour la province de résidence, l’âge de la mère, la parité, le sexe du nourrisson et les naissances multiples.RésultatsEn zone urbaine, pour toute la période étudiée (1991–2005), le quintile de revenu le plus pauvre avait un risque plus élevé de mortalité néonatale (RR ajusté 1,24; IC 95% 1,15–1,34), de mortalité postnéonatale (RR ajusté 1,58; IC 95% 1,41–1,76) et de mort subite du nourrisson (RR ajusté 1,83; IC 95% 1,49–2,26) par rapport au quintile le plus riche. Les taux de mortalité post néonatale et de mort subite du nourrisson ont décliné respectivement de 37 % et de 57 % de 1991–1995 à 2001–2005 alors que le taux de mortalité néonatale n’a pas changé de façon significative. Cette diminution de la mortalité postnéonatale et de la mort subite du nourrisson a été observée dans tous les quintiles de revenu.ConclusionMalgré une diminution de la mortalité postnéonatale et du syndrome de mort subite du nourrisson dans tous les quintiles de revenu, les inégalités subsistent au Canada. Ce résultat démontre le besoin de stratégies efficaces de promotion de la santé visant spécifiquement les populations vulnérables.

Inadequate prenatal care and the risk of stillbirth in the Peruvian Amazon

Major risk factors for stillbirth include lack of skilled birth attendants, low socioeconomic status, poor nutrition, prior stillbirth, advanced maternal age, and the lack of prenatal care [1]. The World Health Organization has published a prenatal care model that includes 4 routine visits for women with no specific risk condition or risk factor, and additional visits for women with health problems or risk factors [2]. During these visits, risk factors should be ascertained (e.g., syphilis screening, measurement of blood pressure) and treatments administered (e.g., iron supplementation). In Peru, the Ministry of Health recommends a schedule of 6 routine prenatal care visits with a series of assessments or interventions to be performed at specific visits [3]. However, for various reasons, the availability, accessibility, and utilization of prenatal care services may be less than optimal. In order to best inform prenatal care services in the Amazon region of Peru, where poverty remains high, we sought to identify risk factors associated with stillbirth in women delivering at the Hospital Iquitos “César Garayar Garcia” in Iquitos, the capital city of Loreto. Data were obtained from a cohort study of birth outcomes, where a random sample of mother–baby medical records had been drawn from the hospital birth registry [4]. Demographic information, admission diagnosis, observations during delivery, and discharge diagnosis were

Seroprevalence of rubella antibodies and determinants of susceptibility to rubella in a cohort of pregnant women in Canada, 2008-2011.

Long term control of rubella and congenital rubella syndrome relies on high population-level immunity against rubella, particularly among women of childbearing age. In Canada, all pregnant women should be screened so that susceptible new mothers can be offered vaccination for rubella before discharge. This study was undertaken to estimate rubella susceptibility in a cohort of pregnant women in Canada and to identify associated socio-economic and demographic factors. Biobanked plasma samples were obtained from the Maternal-Infant Research on Environmental Chemicals (MIREC) study, in which pregnant women were recruited between 2008 and 2011. Socio-demographic characteristics and obstetric histories were collected. Second trimester plasma samples (n=1,752) were tested for rubella-specific IgG using an in-house enzyme-linked immunosorbent assay. The percentage of women with IgG titers <5IU/mL, 5-10IU/mL, and ≥10IU/mL were 2.3%, 10.1%, and 87.6%, respectively. Rates of seronegativity, defined as <5IU/mL, were 3.1% in women who had no previous live birth and 1.6% in women who had given birth previously. Among the latter group, seronegativity was higher in women with high school education or less (adjusted OR (aOR) 5.93, 95% CI 2.08-16.96) or with a college or trade school diploma (aOR 3.82, 95% CI 1.45-10.12), compared to university graduates, and those born outside Canada (aOR 2.60, 95% CI 1.07-6.31). In conclusion, a large majority of pregnant women were found to be immune to rubella. Further research is needed to understand inequalities in vaccine uptake or access, and more effort is needed to promote catch-up measles-mumps-rubella vaccination among socioeconomically disadvantaged and immigrant women of childbearing age.