Deaths Under Five Committee Classification of infant deaths

2018 findings

In 2018, 64% (77 of 120) of the deaths reviewed by the DU5C occurred in infants who were less than one year of age. Chart 11 provides the classification of Infant deaths reviewed by the Deaths Under Five Committee in 2018.

Chart 11: Classification of infant deaths (under age 1 year) reviewed by the Deaths Under Five Committee in 2018

The importance of consistent definitions

Clear understanding and effective classification of sudden and unexpected infant deaths can be hampered by inconsistent use of definitions and terminology. There is variable use of terminology in scientific and medical literature when discussing unexpected infant deaths. Death investigation organizations frequently have individualized approaches to the classification of these deaths.

To accurately study unexpected infant deaths, data needs to be collected from consistently defined records and reports. Collection of consistently defined data sets across many death investigation systems would enable a true analysis of the key factors contributing to these deaths – if the definitions are not the same, it is difficult to compare. The more data we can gather from these tragic deaths, the better positioned our community safety partners will be to develop strategies to prevent similar deaths.

Sudden Infant Death Syndrome (SIDS)

The Ontario death investigation system continues to use the term Sudden Infant Death Syndrome (SIDS) as a classification of a unique category of natural infant deaths, where in the future, a specific underlying natural cause may be found, for example: cardiac, neurologic, metabolic. These are cases that would benefit from further research within the scientific community that may find common underlying factors causing these deaths. The value of categorizing deaths as SIDS (i.e. recognizing SIDS as an “entity”) has been clearly demonstrated through focused research projects. The Back to Sleep Program, for example, had significant public health benefit, contributing to a 53% reduction in deaths (NICHD Back to Sleep Campaign). Research in this area is ongoing by several others.

In Ontario, a death will be attributed to SIDS following a thorough review of all components of the death investigation including: the autopsy; examination of the death scene; review of the clinical history; and a review of the police investigation. The death is then reviewed by the DU5C, who will only attribute the death to SIDS if a consensus decision is reached that the case strictly meets the definition. The DU5C strictly applies the definition of SIDS and excludes cases with even minor deviations. SIDS is only given as a cause of death when all other causes have been ruled out. If the investigation reveals any concerning finding, the cause of death will not be classified as SIDS. It is a finding of exclusion, which is why there were no SIDS cases in 2018

Understanding the manner of death

The following is a discussion about the classification system to ensure those reading this report – families, health care providers, academics, researchers, prevention experts, advocates, media, and others – have insight into Ontario’s approach to help understand the data presented. 

In 57% (44 out of 77 - see data in Chart 11 – Sections 3A+3B+4) of infant deaths reviewed in 2018 by DU5C, the manner of death was “undetermined.” There was one additional case coded as category 1 where the manner of death was undetermined, but there was a medical cause of death noted, bringing the total percentage of undetermined infant deaths to 45/77 or 58%. Undetermined is one of four potential manners of death that would apply in infancy.

The Office of the Chief Coroner applies the following definitions when determining the manner of death:

Natural: a death is natural if it is due to a natural disease or complication thereof; or known complication of diagnosis or treatment of the disease.

Accident: if a death is due to an occurrence, incident or event that happens without foresight or expectation.

Homicide: a death is classified as homicide if it results from the action of a human being killing another human being. 

Undetermined: a full investigation has shown no evidence for any specific classification or there is equal evidence or a significant contest among two or more manners of death.

The manner of death is informed by the autopsy and other investigative findings.  At times, the external and internal examinations completed at the time of autopsy do not reveal an anatomic cause of death. This is more common for infant deaths than youth or adult cases.  

A so-called “negative autopsy” may present in a number of situations including, but not limited to:

• Toxicologic deaths
• Metabolic disorders
• Asphyxial deaths (for example, airway obstruction)
• Infectious disease
• Cardiac diseases (for example, conduction disorders)
• Sudden Infant Death Syndrome (SIDS)

To evaluate for these potential causes, ancillary (additional) testing is completed. This includes: histologic review, vitreous biochemistry, toxicologic analysis, metabolic and genetic testing as well as microbiologic testing for infectious agents. These tests may identify a cause of death from which a specific manner of death can be determined.

It is important to look at how all the information available fits together when investigating death. For example, information about the incident leading to the death can be helpful when considering the autopsy findings in drowning cases.  Investigative information may also be of assistance in determining cause and manner of death. For example, a negative autopsy with observed sudden cardiac arrest with accompanying defibrillator data indicating definitive arrhythmia, may allow an opinion of Sudden Cardiac Death with natural manner. 

Alternatively, in criminal cases, a police investigation may demonstrate clear evidence of airway obstruction while the post mortem examination did not demonstrate any pathologic findings (with cause of death provided as undetermined) leading to the manner of death being provided as homicide. 

The finding of undetermined cause and manner of death is challenging for investigators and family members to receive, given the lack of conclusiveness and/or the fact that other potentials remain. This is especially true within the context of the emotional response that accompanies any death, especially infant deaths.  An undetermined finding follows careful consideration of all the evidence and is a true representation of a thorough investigation. It should not be considered a failure to reach this conclusion. The classification of undetermined allows for future review that may contribute to a better understanding and knowledge about infant deaths. 

The undetermined classification is applied when the death investigation system is not able to clearly delineate the cause and manner of death. Therefore, deaths classified as undetermined may include SIDS deaths.

Unsafe sleep circumstances - Determining the role

Specific findings during post mortem examinations are typically absent in situations of airway obstruction in infants, whether intentional, accidental (for example, overlay during bed sharing) or other unsafe sleep circumstances.  

Potential unsafe sleep circumstances exist along a continuum, from the defined safe environment (i.e. infant sleeping on their back in an uncluttered crib that conforms to regulation) to situations clearly identified as dangerous and likely a direct contributor to death.  The lack of specific pathologic findings of airway obstruction and the potential of other unidentified causes of death have hampered the ability to accurately determine how frequently unsafe sleep circumstances cause infant deaths. These limitations require assigning an undetermined manner of death. However, experience in Ontario, supported by epidemiologic data, is that sleep circumstances may be a contributing factor in many cases. 

Capturing factors potentially related to the death

A risk factor is something associated with ill health, disease and death; it may predispose individuals to develop a particular disease. SIDS has been conceptualized as a “Triple Risk Theory” where a child with (1) an underlying vulnerability (2) at a critical period of development is (3) exposed to an external factor align to lead to the death (Kinney, HC, Thach BT. The sudden infant death syndrome. New England Journal of  Medicine 2009; 361 (8): 795-805).

Triple risk model to explain SIDS

In most literature, accepted risk factors associated with SIDS include: prone positioning, cigarette smoking during pregnancy (and in the post-delivery period) and overheating. These external factors have been defined as modifiable risk factors that predispose the infant to be directly affected by an underlying natural abnormality. 

It is unclear where on the safe sleep continuum specific external factors identified in individual death investigations move from acting as factors that predispose to a natural death (for example, SIDS) to those that directly contribute to an accidental death (for example, airway obstruction during overlay while bed sharing or suffocation on a soft sleep surface). In other words, we don’t know the dividing point on the continuum from natural to accidental death.

The DU5C considers the potential contribution of sleep related circumstances within the context of stratification of risk (based upon literature and experience). During case review by the DU5C, unsafe sleep circumstances found at the death scene preclude the death from being classified as SIDS. Any factor identified at the death scene which might interfere with an infant’s breathing and/or cause entrapment, overlaying, or suffocation is identified. These include: sharing a sleep surface; unsafe sleep surfaces (not intended for infant sleep) such as adult mattresses, waterbeds, couches, car carriers, car seats; a safe sleep surface which is cluttered with toys, blankets and pillows; or a non-approved bassinet or playpen. This is in contrast to previous literature and the practices of some jurisdictions, where these deaths are classified as SIDS.

The association between unsafe sleep environments and sudden unexpected infant deaths has been recognized by death investigators and researchers for many years. The literature, including a number of recent publications, adds to the growing field of knowledge about infant deaths. Two articles of interest are: Sleep Environment Risks for Younger and Older Infants (Colvin, JD, Collie-Akers V, Schunn C, et al. Pediatrics 2014; 134: e406-e412); and the Registered Nurses’ Association of Ontario Working with Families to Promote Safe Sleep for Infants 0-12 months of age. The American Academy of Pediatrics released updated recommendations for a safe infant sleep environment: SIDS and Other Sleep-Related Infant Deaths: Updated 2016 Recommendations for a Safe Infant Sleeping Environment. Pediatrics. 2016;138(5):e20162938

Additional research and documentation of sleep environments at the time of death is necessary to help understand the cause and effect and identify potential prevention strategies. When it is believed that the sleep environment may have contributed to the death, it is included as a contributing factor on the Medical Certificate of Death. This will be captured as data which can be used to inform the development of public health policies and further research into unsafe sleep environments and the potential role in sudden and unexpected infant death.  This is reflected in Category 3A in Charts 10 and 11.   

While the DU5C recognizes the convention of not including contributing factors when the cause of death is undetermined, the committee believes that these cases are a special group and deserve a unique approach. The committee maintains that entering potential contributing factors on the Medical Certificate of Death is more inclusive and recognizes the scope of the death investigation. Similar to the identification of SIDS as a special group, this may allow easier identification for further case study, facilitating future research and potentially informing a public safety approach.

Unsafe sleep environment – What is the data?

Review of Charts 11 demonstrates that there were 45 infant deaths reviewed by the DU5C in 2018  where the manner was deemed to be undetermined (Categories 3A + 3B + 4 and one from category 1). There were 41 (54%) cases (40 were classified as 3A and one was classified as 1) where sleep circumstances may have been a contributing factor.