International comparison of sudden unexpected death ...

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ADC Online First, published on July 10, 2015 as 10.1136/archdischild-2015-308239 Original article

International comparison of sudden unexpected death in infancy rates using a newly proposed set of cause-of-death codes Barry J Taylor,1 Joanna Garstang,2 Adele Engelberts,3 Toshimasa Obonai,4 Aurore Cote,5 Jane Freemantle,6 Mechtild Vennemann,7 Matt Healey,1 Peter Sidebotham,2 Edwin A Mitchell,8 Rachel Y Moon9,10 For numbered affiliations see end of article. Correspondence to Dr Rachel Y Moon, Division of General Pediatrics and Community Health, Children’s National Health System, 111 Michigan Avenue NW, Washington, DC 20010, USA; [email protected] Received 15 January 2015 Revised 3 June 2015 Accepted 17 June 2015

ABSTRACT Background Comparing rates of sudden unexpected death in infancy (SUDI) in different countries and over time is difficult, as these deaths are certified differently in different countries, and, even within the same jurisdiction, changes in this death certification process have occurred over time. Aims To identify if International Classification of Diseases-10 (ICD-10) codes are being applied differently in different countries, and to develop a more robust tool for international comparison of these types of deaths. Methods Usage of six ICD-10 codes, which code for the majority of SUDI, was compared for the years 2002– 2010 in eight high-income countries. Results There was a great variability in how each country codes SUDI. For example, the proportion of SUDI coded as sudden infant death syndrome (R95) ranged from 32.6% in Japan to 72.5% in Germany. The proportion of deaths coded as accidental suffocation and strangulation in bed (W75) ranged from 1.1% in Germany to 31.7% in New Zealand. Japan was the only country to consistently use the R96 code, with 44.8% of SUDI attributed to that code. The lowest, overall, SUDI rate was seen in the Netherlands (0.19/1000 live births (LB)), and the highest in New Zealand (1.00/1000 LB). SUDI accounted for one-third to half of postneonatal mortality in 2002–2010 for all of the countries except for the Netherlands. Conclusions The proposed set of ICD-10 codes encompasses the codes used in different countries for most SUDI cases. Use of these codes will allow for better international comparisons and tracking of trends over time.

INTRODUCTION

To cite: Taylor BJ, Garstang J, Engelberts A, et al. Arch Dis Child Published Online First: [please include Day Month Year] doi:10.1136/ archdischild-2015-308239

Since sudden infant death syndrome (SIDS) was originally defined by Beckwith in 1969 as ‘the sudden death of any infant or young child which is unexpected by history, and in which a thorough postmortem examination fails to demonstrate an adequate cause of death’,1 several definitions have been proposed.2–6 Despite minor changes, the term is generally understood to refer to the sudden, unexpected death in an infant that is unexplained, even after a complete death scene investigation, thorough postmortem (autopsy) and review of the infant’s clinical history. In 1965, SIDS first appeared in the International Classification of Diseases (ICD), V.8, as code 795, and subsequently

What is already known on this topic There are intercountry differences in International Classification of Diseases-10 (ICD-10) coding practices with regard to infant deaths that occur suddenly and unexpectedly. It has therefore been difficult to make comparisons between countries and follow trends in these deaths.

What this study adds We propose and use a set of International Classification of Diseases-10 (ICD-10) codes that encompass the codes that could be used in different countries for sudden unexpected deaths in infancy. Utilization of this more comprehensive grouping of codes will allow for better intercountry comparisons and trends over time.

as code 798.00 in ICD-9.7 8 ICD-10, which came into use in 1994, but was adopted for reporting mortality in subsequent years, uses the code R95 to refer to SIDS (R95.0 refers to SIDS with mention of autopsy; R95.9 to SIDS without mention of autopsy; however, in some countries, such as the USA, R95 without decimals is used).9 In both versions, any other code is given preference. ICD-10 also uses other codes, such as W75 (accidental suffocation or strangulation in bed) or R99 (other illdefined and unspecified causes) to refer to sudden infant deaths that are unexpected and initially unexplained.9 The terms sudden unexpected death in infancy (SUDI) and sudden unexpected infant death (SUID) have recently become more widely used for deaths that occur suddenly and unexpectedly, usually in otherwise healthy infants. As most of these deaths occur during sleep or in a sleep environment, some are also beginning to refer to these deaths as sleep-related infant deaths.3 These terms are descriptive terms that are typically used at the point of presentation when the infant is unexpectedly found dead, and describe both deaths that remain unexplained and those that are subsequently explained following a death scene investigation and autopsy. The final assigned diagnosis code depends

Taylor BJ, et al. Arch Dis Child 2015;0:1–6. doi:10.1136/archdischild-2015-308239

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35 478 0.95 (0.94 to 0.96) 548 1.01 (0.92 to 1.09) 326 0.19 (0.1 to 0.21) 5917 0.60 (0.58 to 0.62) 3283 0.53 (0.51 to 0.55) ICD-10, International Classification of Diseases-10; SUDI, sudden unexpected death in infancy.

1450 0.45 (0.43 to 0.48) 1217 0.50 (0.47 to 0.52)

2712 0.45 (0.43 to 0.47)

37 388 369 20 367 0 30 9677 5164 240 543 946 339 0 0 20 184 5 1 704 636 165 0 3 119 26 13 9 865 703 1931 2655 100 166 567 498 6 200 561 2381 1 50 693 35 123 6 000 525 1662 3 0 877 104 66 2 824 482 933 2 1 416 84 14 2 457 610 750 0 73 306 75 13

Live births R95 (sudden infant death syndrome) R96 (other sudden death, cause unknown) R98 (unattended death) R99 (other ill-defined and unspecified causes of mortality) W75 (accidental suffocation and strangulation in bed) W78 (inhalation of gastric contents) + W79 (inhalation and ingestion of food, causing obstruction of respiratory tract) Total Rate (95% CI)

New Zealand The Netherlands Japan Germany England and Wales Canada

Eight countries (Australia, Canada, Germany, Japan, the Netherlands, New Zealand, England and Wales, USA) were identified for comparison. All were considered high-income, and there was a collaborator in each place who could provide the necessary information. All ICD-10 codes were examined independently by two authors (BJT and EAM)—both of whom are experienced clinicians and researchers in the area of postneonatal mortality—to identify an a priori list of all codes that could possibly be used when the cause of death was not clear.9 ICD-10 codes are listed in table 1, and specifically include codes that have been used when it is assumed that bed-sharing contributed to the death (eg, W75: accidental suffocation and strangulation in bed) as well as codes describing terminal events that would be secondary (ie, agonal) rather than primary causes of death under 1 year of age (eg, W78: inhalation of gastric contents; W99: inhalation and ingestion of food causing obstruction of respiratory tract). Authors from each of the eight countries accessed publicly available national vital statistics data to identify the number of deaths between birth and 1 year of age with these specific ICD-10 codes for the years 2002–2010. The number and respective rates per 1000 live births (LB) were calculated with 95% CIs. Postneonatal rates were calculated as the number of deaths between 28 and 365 days of age per 1000 LB. Linear regression analysis was conducted for each country, predicting total SUDI rates over the years 2002–2010. Because this investigation used publicly available anonymous data, no ethical committee approval was required.

Australia

METHODS

Table 1 Deaths by ICD-10 code,9 total deaths and SUDI rates (per 1000 live births), 2002–2010

upon the findings of the death scene investigation and autopsy; however, there is great variability in investigative practices. Further, a high proportion of all SUDI do not acquire a conclusive diagnosis, even following a thorough investigation. Furthermore, in many countries, there has been evidence of ‘diagnostic drift’ over the years because of improved protocols for death scene investigation, and as different risk factors for SIDS, such as prone positioning, are identified and then used (often inappropriately) as indicating a cause of death.10 Many countries are using terms such as ‘accidental suffocation and strangulation in bed’, ‘positional asphyxia’ and ‘unascertained’ for these sleep-related deaths. However, difficulties arise as there are no reliable pathological markers for suffocation (whether accidental or intentional), and, in most cases, it is difficult to conclusively state whether a death has been due to asphyxia. As a result, although most countries are now coding cause of infant deaths using WHO’s ICD-10 codes9 or by translating local codes to ICD-10 codes (UK and Japan), there is much variability in coding. The variability in coding makes it difficult to compare rates of SIDS and SUDI across countries, and the only way to compare rates between countries has been to use total postneonatal (28–365 days)11 or 1 to 5-month mortality rates.12 However, this comparison is not entirely reliable, as postneonatal and 1 to 5-month mortality rates include all causes of death, including deaths with explained aetiology. We, therefore, investigated the possibility of identifying all ICD-10 codes that could potentially be used for initially unexplained SUDI and then compared their use across a range of countries where such codes were used. We excluded codes that indicate a clear medical (eg, infection, metabolic disorder, arrhythmia, congenital anomaly) or forensic (eg, head injury or other trauma) cause, even if these may initially present as SUDI. Our aim was to identify if ICD-10 codes were being applied differently in different countries and to develop a more robust tool for international comparison of these types of deaths.

USA

Original article

Taylor BJ, et al. Arch Dis Child 2015;0:1–6. doi:10.1136/archdischild-2015-308239

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Original article Figure 1 International Classification of Diseases-10 (ICD-10) codes as percentages of the total sudden unexpected death in infancy (SUDI) per country, 2002–2010.

RESULTS All eight countries provided data on deaths in 2002–2010. Because there were so few deaths in the W78 and W79 categories, these data were combined. In Japan, the Ministry of Health, Labour and Welfare classify infant deaths by locally developed codes, which can be translated to ICD-10 codes. While postneonatal deaths in the UK are coded directly with ICD-10 codes, there is a different death certification process for stillbirths and neonatal deaths13 that translates main infant and maternal conditions to ICD-10 codes using an hierarchical classification system to assign nine mutually exclusive causes of death.14 Any deaths for which ICD-10 codes R95–R98 are given as a main condition in the infant are coded as sudden infant death. For

the purposes of this international comparison, we included all and only those deaths coded as sudden infant death. The total number of deaths between 2002 and 2010 in these eight countries, with breakdown by ICD-10 code, is shown in table 1. There is great variability in how each country codes SUDI (figure 1). The proportion of deaths coded as R99 (other illdefined and unspecified causes) ranges from 3.6% in New Zealand to 36.5% in the Netherlands, and the proportion of deaths coded as W75 (accidental suffocation and strangulation in bed) ranges from 1.1% in Germany to 33.6% in New Zealand. Furthermore, Japan is the only country that consistently uses R96 (other sudden death, cause unknown) to code SUDI, with 44.8% of SUDI coded in this manner. Similarly,

Figure 2 Rates of deaths coded as R95 (sudden infant death syndrome, SIDS), per country, 2002–2010.

Taylor BJ, et al. Arch Dis Child 2015;0:1–6. doi:10.1136/archdischild-2015-308239

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Original article Table 2 Postneonatal (28–365 days) mortality rates (per 1000 live births) and SUDI as a proportion of postneonatal mortality, 2000–2010 Country

2002

2003

2004

2005

2006

2007

2008

2009

2010

Mean PNMR

SUDI as proportion of PNMR

Australia Canada England and Wales Germany Japan The Netherlands New Zealand USA

1.58 1.48 1.7 1.47 1.35 1.23 1.98 2.29

1.46 1.32 1.7 1.48 1.32 1.18 2.08 2.22

1.46 1.28 1.6 1.45 1.35 1.04 2.60 2.25

1.42 1.32 1.6 1.40 1.36 1.25 1.86 2.32

1.52 1.34 1.5 1.25 1.30 1.09 2.50 2.22

1.25 1.28 1.5 1.22 1.28 0.88 2.19 2.33

1.24 1.36 1.4 1.18 1.34 0.96 2.06 2.32

1.22 1.23 1.4 1.18 1.22 0.99 2.12 2.21

1.14 1.21 1.3 1.15 1.20 1.00 1.95 2.1

1.37 1.31 1.52 1.31 1.30 1.07 2.14 2.25

0.37 0.35 0.30 0.40 0.46 0.18 0.47 0.42

SUDI, sudden unexpected death in infancy; PNMR, postneonatal mortality rate.

there is variability in the proportion of SUDI that are coded as R95 (SIDS); this ranged from 32.6% in Japan to 72.5% in Germany. Figure 2 demonstrates the rate of deaths coded as R95 in each country between 2002 and 2010. Postneonatal mortality rates (per 1000 LB), as shown in table 2, range from 1.07/1000 LB in the Netherlands to 2.25/1000 LB in the USA. US A and New Zealand have higher postneonatal mortality rates than the other countries, with a less marked decline over years. Using this more comprehensive grouping of ICD-10 codes, SUDI comprises one-third to half of all postneonatal deaths for all countries except for the Netherlands (18%). The proportion of postneonatal mortality attributed to SUDI in the Netherlands is 40% lower than any of the other countries. Figure 3 shows the SUDI rates ( per 1000 LB) per country per year using these ICD-10 codes. The lowest overall SUDI rate is seen in the Netherlands (0.19/1000 LB), and mid-range SUDI rates (0.4–0.6/1000 LB) are seen in England and Wales (0.45/ 1000 LB), Canada (0.45/1000 LB), Australia (0.50/1000 LB), Germany (0.53/1000 LB) and Japan (0.60/1000 LB). The highest SUDI rates are in the USA (0.95/1000 LB) and New Zealand (1.01/1000 LB). Further, the linear trend for this period, as calculated in the linear regression analysis, is shown for each country in figure 4. All countries except the USA showed a downward pattern of total SUDI rates across the target year range, and these downward trends were statistically

significant for Australia, Canada, England and Wales, Germany, Japan and the Netherlands (table 3).

DISCUSSION Since SIDS was recognised in the 1960s, other causes of SUDI have been identified, and multiple ICD-10 codes are used variably in different countries. No code is used consistently among countries. This makes it difficult to make intercountry comparisons and to compare mortality over time. We used a more comprehensive set of ICD-10 codes that encompassed those that could be used in different countries for SUDI, and found that there was great variability in how different countries coded these deaths. Therefore, usage of this more comprehensive set of ICD-10 codes may allow for intercountry comparisons and trends over time. Further, this approach is not specific to examining and comparing rates of SUDI; this methodology could be used for any condition for which there may be inconsistent coding protocols or diagnostic drift. When this more comprehensive set of codes is used, some interesting patterns emerge. There is great variability in the proportion of SUDI that are coded as R95 (SIDS). When SIDS rates are compared, the Netherlands and Japan have been noted to have the lowest. However, the Netherlands has the highest proportion of SUDI categorised as R99 (other ill-defined and unspecified causes of mortality), and Japan is the only country

Figure 3 Sudden unexpected death in infancy rates ( per 1000 live births) per country, per year, using new set of International Classification of Diseases-10 codes.

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Taylor BJ, et al. Arch Dis Child 2015;0:1–6. doi:10.1136/archdischild-2015-308239

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Original article

Figure 4 Total sudden unexpected deaths in infancy rates per country, 2002–2010.

that consistently uses R96 (other sudden death, cause unknown). While other countries may rarely use this R96 code (the other seven countries in this survey collectively reported six cases in 2002–2010), Japan used this code 2655 times in this 9-year span. This suggests that different versions of diagnostic drift may be occurring, with individual countries having preference for specific ICD-10 codes. Autopsy rates in individual countries may also impact assignment of ICD-10 codes. In the eight countries surveyed, it is estimated that autopsy rates for sudden and unexpected infant deaths ranged from 99% (New Zealand, England and Wales). However, the comprehensiveness of the autopsy protocol may be inconsistent between countries. Further, the lack of an autopsy examination in more than 80% of SUDI in Japan may partially explain why so many deaths were coded as R96. It also suggests that Japanese codes may

Table 3 Results of linear regression analysis per country of total SUDI rate, 2002–2010 Country

β

SE β

Pr(>|t|)

Adjusted R2

Australia Canada England and Wales Germany Japan The Netherlands New Zealand USA

−0.02 −0.01 −0.02 −0.03 −0.02 −0.02 −0.01 0.00

0.005 0.003 0.003 0.003 0.005 0.005 0.012 0.004

0.001** 0.017* 0.000*** 0.000*** 0.013* 0.008** 0.294NS 0.536NS

0.73 0.51 0.88 0.82 0.54 0.61 0.03 −0.08

*p