Abstract
Background
Rates 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.
Objectives
This 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.
Methods
The 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.
Results
In 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.
Conclusion
This 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.
Key Words: Infant mortality, social class, sudden infant death
Résumé
Contexte
La 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.
Objectifs
La 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.
Méthodes
Le 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.
Résultats
En 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.
Conclusion
Malgré 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.
Mots Clés: mort subite du nourrisson, mortalité infantile, statut socioéconomique
Footnotes
Acknowledgements: The authors are grateful to Statistics Canada and to provincial and territorial vital statistics registrars for providing access to the births and deaths files, and to Juan Andrés León and Michael Tjepkema for reviewing and commenting on an earlier version of this article.
Conflict of Interest: None to declare.
References
- 1.Health Canada. Canadian Perinatal Health Report 2003. 2003. [Google Scholar]
- 2.Public Health Agency of Canada. Perinatal Health Indicators for Canada 2011. 2012. [Google Scholar]
- 3.Arntzen A, Samuelsen SO, Bakketeig LS, Stoltenberg C. Socioeconomic status and risk of infant death. A population-based study of trends in Norway, 1967–1998. Int J Epidemiol. 2004;33(2):279–88. doi: 10.1093/ije/dyh054. [DOI] [PubMed] [Google Scholar]
- 4.Oakley L, Maconochie N, Doyle P, Dattani N, Moser K. Multivariate analysis of infant death in England and Wales in 2005–06, with focus on socioeconomic status and deprivation. Health Stat Q. 2009;42:22–39. doi: 10.1057/hsq.2009.15. [DOI] [PubMed] [Google Scholar]
- 5.Joseph KS, Liston RM, Dodds L, Dahlgren L, Allen AC. Socioeconomic status and perinatal outcomes in a setting with universal access to essential health care services. CMAJ. 2007;177:583–90. doi: 10.1503/cmaj.061198. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Luo ZC, Wilkins R, Kramer MS. Effect of neighbourhood income and maternal education on birth outcomes: A population-based study. CMAJ. 2006;174:1415–20. doi: 10.1503/cmaj.051096. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Luo ZC, Kierans WJ, Wilkins R, Liston RM, Mohamed J, Kramer MS. Disparities in birth outcomes by neighborhood income: Temporal trends in rural and urban areas, British Columbia. Epidemiol. 2004;15:679–86. doi: 10.1097/01.ede.0000142149.34095.88. [DOI] [PubMed] [Google Scholar]
- 8.Injury Prevention Committee, Canadian Paediatric Society. Reducing the risk of sudden infant death. Paediatr Child Health. 1996;1:63–67. [Google Scholar]
- 9.Rusen ID, Liu S, Sauve R, Joseph KS, Kramer MS. Sudden infant death syndrome in Canada: Trends in rates and risk factors, 1985–1998. Chronic Dis Can. 2004;25:1–6. [PubMed] [Google Scholar]
- 10.Gilbert NL, Fell DB, Joseph KS, Liu S, León JA, Sauve R. 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. Paediatr Perinat Epidemiol. 2012;26:124–30. doi: 10.1111/j.1365-3016.2011.01248.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Fair M, Cyr M, Allen A, Wen SW, Guyon G, MacDonald RC. An assessment of the validity of a computer system for probabilistic record linkage of birth and infant death records in Canada. The Fetal and Infant Health Study Group. Chronic Dis Can. 2000;21:8–13. [PubMed] [Google Scholar]
- 12.Public Health Agency of Canada. Canadian Perinatal Health Report. 2008. [Google Scholar]
- 13.Wilkins R, Khan S. PCCF+ Version 5J User’s Guide. Automated geographic coding based on the Statistics Canada Postal Code Conversion files, including postal codes through May 2011. Report 82F0086-XDB. Ottawa: Statistics Canada; 2011. [Google Scholar]
- 14.du Plessis V, Beshiri R, Bollman RD, Clemenson H. Definition of Rural. Rural and Small Town Canada Analysis Bulletin. Vol. 3, No. 3. Report 21-006-XIE. Ottawa: Statistics Canada; 2001. [Google Scholar]
- 15.Wilcox AJ, Weinberg CR, Basso O. On the pitfalls of adjusting for gestational age at birth. Am J Epidemiol. 2011;174(9):1062–68. doi: 10.1093/aje/kwr230. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Lin DY, Wei LJ. The robust inference for the Cox proportional hazards model. J Am Stat Assoc. 1989;84:1074–78. doi: 10.1080/01621459.1989.10478874. [DOI] [Google Scholar]
- 17.Allison PD. Survival Analysis Using SAS®: A Practical Guide. Second. Cary, NC: SAS Institute Inc.; 2010. [Google Scholar]
- 18.Auger N, Roncarolo F, Harper S. Increasing educational inequality in preterm birth in Quebec, Canada, 1981–2006. J Epidemiol Community Health. 2011;65:1091–96. doi: 10.1136/jech.2009.102350. [DOI] [PubMed] [Google Scholar]
- 19.Auger N, Park AL, Harper S, Daniel M, Roncarolo F, Platt RW. Educational inequalities in preterm and term small-for-gestational-age birth over time. Ann Epidemiol. 2012;22:160–67. doi: 10.1016/j.annepidem.2012.01.004. [DOI] [PubMed] [Google Scholar]
- 20.Leach CE, Blair PS, Fleming PJ, Smith IJ, Platt MW, Berry PJ, et al. Epidemiology of SIDS and explained sudden infant deaths. Pediatrics. 1999;104:e43. doi: 10.1542/peds.104.4.e43. [DOI] [PubMed] [Google Scholar]
- 21.Wood AM, Pasupathy D, Pell JP, Fleming M, Smith GC. Trends in socioeconomic inequalities in risk of sudden infant death syndrome, other causes of infant mortality, and stillbirth in Scotland: Population based study. BMJ. 2012;344:e1552. doi: 10.1136/bmj.e1552. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Fleming PJ, Blair PS, Bacon C, Bensley D, Smith I, Taylor E, et al. Environment of infants during sleep and risk of the sudden infant death syndrome: Results of 1993–5 case-control study for confidential inquiry into stillbirths and deaths in infancy. BMJ. 1996;313:191–95. doi: 10.1136/bmj.313.7051.191. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Public Health Agency of Canada. What Mothers Say: The Canadian Maternity Experiences Survey. 2009. [Google Scholar]
- 24.Mitchell EA, Milerad J. Smoking and the sudden infant death syndrome. Rev Environ Health. 2006;21(2):81–103. doi: 10.1515/REVEH.2006.21.2.81. [DOI] [PubMed] [Google Scholar]
- 25.Hauck FR, Thompson JM, Tanabe KO, Moon RY, Vennemann MM. Breastfeeding and reduced risk of sudden infant death syndrome: A meta-analysis. Pediatrics. 2011;128(1):103–10. doi: 10.1542/peds.2010-3000. [DOI] [PubMed] [Google Scholar]
- 26.Wilkins R. Neighbourhood income quintiles derived from Canadian postal codes are apt to be misclassified in rural but not urban areas. Ottawa: Statistics Canada; 2004. [Google Scholar]