Abstract
Background
Although high rates of COVID-19-related deaths have been reported for people with intellectual disabilities during the first 2 years of the pandemic, it is unknown to what extent the pandemic has impacted existing mortality disparities for people with intellectual disabilities. In this study, we linked a Dutch population-based cohort that contained information about intellectual disability statuses with the national mortality registry to analyse both cause-specific and all-cause mortality in people with and without intellectual disabilities, and to make comparisons with pre-pandemic mortality patterns.
Methods
This population-based cohort study used a pre-existing cohort that included the entire Dutch adult population (everyone aged ≥18 years) on Jan 1, 2015, and identified people with presumed intellectual disabilities through data linkage. For all individuals within the cohort who died up to and including Dec 31, 2021, mortality data were obtained from the Dutch mortality register. Therefore, for each individual in the cohort, information was available about demographics (sex and date of birth), indicators of intellectual disability, if any, based on chronic care and (social) services use, and in case of death, the date and underlying cause of death. We compared the first 2 years of the COVID-19 pandemic (2020 and 2021) with the pre-pandemic period (2015–19). The primary outcomes in this study were all-cause and cause-specific mortality. We calculated rates of death and generated hazard ratios (HRs) using Cox regression analysis.
Findings
At the start of follow-up in 2015, 187 149 Dutch adults with indicators of intellectual disability were enrolled and 12·6 million adults from the general population were included. Mortality from COVID-19 was significantly higher in the population with intellectual disabilities than in the general population (HR 4·92, 95% CI 4·58–5·29), with a particularly large disparity at younger ages that declined with increasing age. The overall mortality disparity during the COVID-19 pandemic (HR 3·38, 95% CI 3·29–3·47) was wider than before the pandemic (3·23, 3·17–3·29). For five disease groups (neoplasms; mental, behavioural, and nervous system; circulatory system; external causes; and other natural causes) higher mortality rates were observed in the population with intellectual disabilities during the pandemic than before the pandemic, and the pre-pandemic to during the pandemic difference in mortality rates was greater in the population with intellectual disabilities than in the general population, although relative mortality risks for most other causes remained within similar ranges compared with pre-pandemic years.
Interpretation
The impact of the COVID-19 pandemic on people with intellectual disabilities has been greater than reflected by COVID-19-related deaths alone. Not only was the mortality risk from COVID-19 higher in people with intellectual disabilities than in the general population, but overall mortality disparities were also further exacerbated during the first 2 years of the pandemic. For disability-inclusive future pandemic preparedness this excess mortality risk for people with intellectual disabilities should be addressed.
Funding
Dutch Ministry of Health, Welfare, and Sport and Netherlands Organization for Health Research and Development.
Introduction
People with intellectual disabilities generally have health disparities and barriers in accessing adequately tailored care, resulting in poor health outcomes and premature death.1, 2, 3 Intellectual disabilities can be caused by a range of genetic, infectious, birth-related, or environmental factors, and are characterised by substantial cognitive impairment and limitations in adaptive behaviour with onset before adulthood, with an estimated prevalence of approximately 1·5% in high-income countries.4, 5, 6
During the COVID-19 pandemic, people with intellectual disabilities were at a particular risk for poor health outcomes for at least three reasons. First, people with intellectual disabilities had an increased risk of contracting SARS-CoV-2.7, 8 Close encounters in care and social settings are common, especially within residential care facilities, and potentially low (health) literacy complicated complying with restrictive prevention measures, such as social distancing or wearing face masks.9, 10, 11 Second, immunodeficiencies, generally poorer overall health, and health inequities put people with intellectual disabilities at a greater risk of serious illness and death from COVID-19 than people in the general population, particularly in the presence of a syndromic intellectual disability.2, 12, 13, 14, 15 Finally, COVID-19 might have exacerbated existing disparities for people with intellectual disabilities.10, 16 Mortality risks have always been greater for people with intellectual disabilities than for people in the general population.17, 18, 19 These existing mortality disparities are associated with risk factors in people with intellectual disabilities (eg, multimorbidity and obesity20) and factors related to provision of care and health services.1, 3, 19 The COVID-19 pandemic disrupted routine provision of care, as residential facilities were closed for visitors during lockdowns, daytime and group activities were cancelled, and staff needed to spend more time on patients in isolation and quarantine.21, 22
Research in context.
Evidence before this study
We searched PubMed for articles published in English from database inception up to Aug 11, 2022, using the following search terms: (“COVID” OR “coronavirus”) AND (“intellectual disab*” OR “learning disab*“) AND (“mortality” OR “death”). The search identified 76 articles, 22 of which reported primary data on COVID-19-related deaths. Most studies analysed data from the first epidemic waves only, and six studies included data from the start of the pandemic up to the first months of 2021. Outcomes mostly concerned COVID-19 case fatalities to identify risk factors and four studies included all-cause mortality to calculate excess mortality rates, but no studies specified cause-specific mortality from causes other than COVID-19. Existing studies showed a greater mortality risk for people with intellectual disabilities in general, and for certain subgroups (eg, those with Down syndrome or living in congregate settings) in particular. Studies that addressed excess mortality from COVID-19 showed an association with intellectual disability, among other factors.
Added value of this study
This population-based cohort study is the first, to our knowledge, to report cause-specific mortality for two complete years (2020 and 2021) since the start of the pandemic, providing robust evidence for increased mortality risks from COVID-19 for people with intellectual disabilities, and to specify to what extent other causes of death were affected. Our study showed that the full impact of the COVID-19 pandemic has been much greater than indicated by reported deaths due to COVID-19 alone. Existing mortality disparities between people with and without intellectual disabilities have been further widened compared with the period 2015–19.
Implications of all the available evidence
The health risks for people with intellectual disabilities warrant targeted policy making regarding protective measures for the current pandemic and future pandemic preparedness that go beyond the causative agent of a pandemic alone. This study shows the need for better monitoring of vulnerable populations, such as people with disabilities, who are at risk of otherwise being overlooked, with marked consequences.
High mortality rates from COVID-19 among people with intellectual disabilities have been reported, particularly for people with Down syndrome, and for residents of long-term care facilities.23, 24, 25, 26 However, to our knowledge, no evidence is available on the effect of the pandemic on mortality from all other causes excluding COVID-19 and the effect on existing mortality disparities between people with and without intellectual disabilities. Investigation of cause-specific mortality is pivotal for understanding the full impact the pandemic had on people with intellectual disabilities, but could also inform future public health policies. Although disability status information is essential for such investigations, this variable is not routinely available in surveillance systems set up to monitor COVID-19, nor is it part of standard mortality statistics. Therefore, data linkage at the population level is needed to combine information on disability status with causes of death. In this study, we linked a Dutch population-based cohort that contained information about intellectual disability statuses with the national mortality registry to analyse both cause-specific and all-cause mortality in people with and without intellectual disabilities, and to make comparisons with pre-pandemic mortality patterns.
Methods
Study design and population
This population-based cohort study used a pre-existing cohort that included the entire Dutch adult population (aged ≥18 years) on Jan 1, 2015, and identified people with presumed intellectual disabilities through data linkage.27 For all individuals within the cohort who died up to and including Dec 31, 2021, mortality data were obtained from the Dutch mortality register. Therefore, for each individual in the cohort, information was available about demographics (sex and date of birth), indicators of intellectual disability, if any, based on chronic care and (social) services use, and in case of death, the date and underlying cause of death. The databases needed for this study were available for statistical and scientific research as non-public microdata within a secure, digital research environment at Statistics Netherlands, the Dutch national statistics office.28 The Radboud University Medical Center institutional ethics committee waived the need for ethics approval as this was a large-scale anonymous database study with posthumous investigation of mortality data (reference 2017-3921). We report our results in accordance with the STROBE statement.29
The population with intellectual disabilities was determined by the presence of indicators of intellectual disability, as actual intellectual disability diagnoses are not saved in any national database. Indicators of intellectual disability consisted of a record in one of the national databases for chronic care or social services where “intellectual disability” was noted as a reason for calling upon one or more services. When service access was requested, an individual's intellectual disability diagnosis was verified, but information about the diagnosis was not included in service records.27 This method identified individuals with presumed moderate to severe intellectual disabilities who either received residential intellectual disability care or non-residential intellectual disability-related chronic care, and individuals with mild intellectual disabilities who received support in the social domain. This method has been applied to other studies related to health and intellectual disability before, including investigation of mortality.16, 30 All individuals without indicators of intellectual disability were analysed as members of the general population.
Outcomes
The primary outcomes in this study were all-cause and cause-specific mortality. Dutch law prescribes mandatory notification of the cause of death. Forms specifying the cause and location of death are collected, processed, and coded by Statistics Netherlands. The disease or injury initiating the train of morbid events or fatal injury is recorded as the cause of death in the mortality registry using the International Statistical Classification of Diseases and Related Health Problems, tenth revision (ICD-10).31 COVID-19-related mortality was defined by the ICD-10 emergency codes for proven (U07.1) or suspected COVID-19 (not tested or virus not identified; U07.2). The database used for this study could contain only a single underlying cause of death.
Statistical analysis
Demographics were presented as frequencies (with percentages) or means (with SD). We reported the number of observed deaths in the population with intellectual disabilities and the general population and calculated mortality rates per 10 000 population per year (2015–2021). Crude mortality rates were calculated using the mid-period population size as the denominator. Age-standardised and sex-standardised mortality rates from the general population were applied to the population with intellectual disabilities to calculate expected deaths in this group. Relative mortality risks for the population with intellectual disabilities relative to the general population were expressed as hazard ratios (HRs) with 95% CIs for all-cause mortality and COVID-19-related mortality using Cox regression analysis to account for potential differences in survival time and to adjust for different distributions of age and sex in both groups. For the pre-pandemic period, follow-up time was from Jan 1, 2015, to time of death or Dec 31, 2019, and follow-up during the pandemic was calculated for all people alive on Jan 1, 2020, until time of death or Dec 31, 2021. Results were presented for the entire group, and for age and sex groups separately.
Specific causes of death other than those that were COVID-19-related were grouped into the same six umbrella categories as used by Statistics Netherlands, as follows: neoplasms; circulatory system; respiratory system; mental, behavioural, and nervous system; external (non-natural) causes; and other natural causes.32 For each of these groups, we calculated mortality rates and generated HRs to compare the population with intellectual disabilities with the general population for the pre-pandemic (2015–19) and pandemic period (2020–21), with deaths from other causes being censored at the time of death. The frequency distribution of individual causes (specified by their three position ICD-10 code) within each of the six disease groups was compared before and during the pandemic using χ2 tests.
p<0·05 was considered to indicate a statistically significant difference. All analyses were done in SPSS version 25.0.
Role of the funding source
The funders of the study had no role in the study design, data collection, data analysis, data interpretation, or writing of the report.
Results
At the start of follow-up in 2015, 187 149 Dutch adults with indicators of intellectual disability were enrolled in the cohort (1·45% intellectual disability prevalence; population with intellectual disabilities) and 12·6 million adults from the general population were included. The population with intellectual disabilities consisted of more male individuals than female individuals (107 370 [57·4%] of 187 149 people vs 78 779 [42·6%] of 187 149 people) and was younger than the general population (mean age 39·6 years [SD 15·6] vs 48·3 years [17·8]). During the 7 years of follow-up, 16 528 deaths in the population with intellectual disabilities and 1 057 163 deaths in the general population were entered in the mortality register (table 1 ). The median follow-up in both groups was 365 weeks, of which 261 were before the COVID-19 pandemic and 104 weeks were during the pandemic.
Table 1.
Cohort characteristics on Jan 1, 2015, and deaths observed during follow-up (2015–21)
| General population (n=12 677 768) | Population with intellectual disabilities (n=187 149) | ||
|---|---|---|---|
| Person-years generated | 85 370 489 | 1 258 873 | |
| Sex | |||
| Male | 6 196 789 (48·9%) | 107 370 (57·4%) | |
| Female | 6 480 979 (51·1%) | 78 779 (42·6%) | |
| Age, years* | 48·3 (17·8) | 39·6 (15·6) | |
| Age group, years* | |||
| 18–24 | 1 362 047 (10·7%) | 44 343 (23·7%) | |
| 25–34 | 1 931 948 (15·2%) | 36 615 (19·6%) | |
| 35–44 | 2 225 395 (17·6%) | 32 514 (17·4%) | |
| 45–54 | 2 457 868 (19·4%) | 37 109 (19·8%) | |
| 55–64 | 2 104 631 (16·6%) | 25 140 (13·4%) | |
| 65–74 | 1 551 963 (12·2%) | 8770 (4·7%) | |
| ≥75 | 1 043 916 (8·2%) | 2658 (1·4%) | |
| Intellectual disability groups | |||
| Residential intellectual disability | .. | 91 064 (48·7%) | |
| Non-residential intellectual disability | .. | 27 007 (14·4%) | |
| Mild intellectual disability | .. | 69 078 (36·9%) | |
| Deaths, n (rate per 10 000 people) | |||
| 2015 | 143 351 (113·7) | 2041 (109·7) | |
| 2016 | 144 971 (115·7) | 2134 (115·3) | |
| 2017 | 145 762 (117·0) | 2213 (120·3) | |
| 2018 | 148 556 (119·9) | 2418 (132·3) | |
| 2019 | 146 855 (119.3) | 2291 (126·2) | |
| 2020 | 162 919 (133·2) | 2603 (144·4) | |
| 2021 | 164 750 (135·6) | 2828 (158·1) | |
Data are n (%) or mean (SD), unless otherwise indicated.
Age and age groups refer to age at enrolment in 2015.
In the pre-pandemic years 2015–19, crude mortality rates in the population with intellectual disabilities were between 109·7 per 10 000 people per year and 132·3 per 10 000 people per year (2041 to 2418 deaths per year), and between 113·7 per 10 000 people per year and 119·9 per 10 000 people per year in the general population (143 351 to 148 555 deaths per year; table 1). The HR for people with intellectual disabilities relative to the general population for the entire pre-pandemic period between 2015 and 2019 was 3·23 (95% CI 3·17–3·29; table 2 ). In 2020 and 2021, crude mortality rates in the population with intellectual disabilities increased to 144·4 per 10 000 people per year and 158·1 per 10 000 people per year (2603 and 2828 deaths), and to 133·2 per 10 000 people per year and 135·6 per 10 000 people per year in the general population (162 919 and 164 750 deaths), resulting in an HR of 3·38 (95% CI 3·29–3·47; Table 1, Table 2). If the mean pre-pandemic mortality rate in the population with intellectual disabilities (123·5) applied during the pandemic, around 1000 fewer deaths would be expected in the population with intellectual disabilities in 2020 (2271 instead of 2603 observed) and 2021 (2210 instead of 2828 observed).
Table 2.
Cause-specific mortality by main disease groups in 2015–19 and 2020–21
|
2015–19 |
2020–21 |
|||||
|---|---|---|---|---|---|---|
| Crude rates per 10 000 population |
HR (95% CI) | Crude rates per 10 000 population |
HR (95% CI) | |||
| General population | Population with intellectual disabilities | General population | Population with intellectual disabilities | |||
| Neoplasms | 36·6 | 26·2 | 1·59 (1·53–1·66) | 37·6 | 29·6 | 1·70 (1·60–1·80) |
| Mental, behavioural, and nervous system | 16·3 | 16·2 | 4·72 (4·49–4·97) | 15·9 | 18·3 | 4·93 (4·56–5·33) |
| Circulatory system | 30·2 | 24·0 | 3·13 (3·00–3·27) | 29·7 | 24·9 | 3·03 (2·84–3·24) |
| Respiratory system | 10·0 | 15·1 | 5·61 (5·32–5·92) | 8·2 | 12·4 | 4·96 (4·51–5·45) |
| External causes | 6·1 | 5·2 | 2·01 (1·83–2·20) | 6·9 | 6·8 | 2·53 (2·23–2·87) |
| Other natural causes | 19·9 | 34·0 | 6·67 (6·43–6·91) | 20·3 | 38·0 | 6·06 (5·74–6·40) |
| COVID-19 | .. | .. | .. | 16·4 | 22·1 | 4·92 (4·58–5·29) |
| All causes | 117·1 | 120·7 | 3·23 (3·17–3·29) | 134·4 | 151·2 | 3·38 (3·29–3·47) |
Crude rates calculated per 10 000 people per year. HRs are adjusted for age and sex and compare the population with intellectual disabilities with the general population. HR=hazard ratio.
COVID-19 was the most reported specific cause of death in the population with intellectual disabilities in 2020–21, accounting for 765 deaths (22·1 per 10 000 people per year), whereas between 166 and 178 deaths were expected on the basis of COVID-19-related mortality in the general population (38 580 deaths; 16·4 per 10 000 people per year), resulting in an HR of 4·92 (95% CI 4·58–5·29; Table 2, Table 3 ).
Table 3.
Characteristics of deaths caused by suspected or confirmed COVID-19 in 2020–21
| Observed deaths in the general population (n=11 948 273) |
Population with intellectual disabilities (n=176 052) |
||||
|---|---|---|---|---|---|
| Observed deaths | Expected deaths* | HR (95% CI) | |||
| Entire group, n (rate per 10 000 people) | 38 580 (16·4) | 765 (22·1) | 171 (166–178) | 4·92 (4·58–5·29) | |
| Sex, n (rate per 10 000 people) | |||||
| Male | 20 826 (18·1) | 460 (23·1) | 116 (113–121) | 4·33 (3·94–4·75) | |
| Female | 17 754 (14·7) | 305 (20·6) | 55 (53–57) | 6·16 (5·50–6·90) | |
| Age at death, years | 81·9 (9·8) | 67·7 (12·2) | .. | .. | |
| Age group, years, n (rate per 10 000 people) | |||||
| 23–29 | 13 (0·0) | <10 | <10 | 22·54 (9·60–52·92) | |
| 30–39 | 69 (0·2) | 22 (3·0) | <10 | 18·07 (11·17–29·25) | |
| 40–49 | 288 (0·7) | 42 (6·7) | <10 | 10·00 (7·23–13·83) | |
| 50–59 | 1262 (2·6) | 165 (24·2) | 19 (18–20) | 8·91 (7·58–10·49) | |
| 60–69 | 4350 (10·9) | 252 (60·5) | 49 (48–50) | 5·63 (4·96–6·39) | |
| 70–79 | 11 908 (44·4) | 193 (162·5) | 57 (57–58) | 3·85 (3·34–4·44) | |
| ≥80 | 20 690 (188·6) | 82 (418·8) | 39 (39–40) | 2·57 (2·07–3·19) | |
| Location of death† | |||||
| Hospital | 15 143 (39·3%) | 265 (34·6%) | .. | .. | |
| Care facility | 19 755 (51·2%) | 453 (59·2%) | .. | .. | |
| Home | 3415 (8·9%) | 40 (5·2%) | .. | .. | |
| Other or unknown | 267 (0·7%) | <10 | .. | .. | |
| Year of death, n (rate per 10 000 people)† | |||||
| 2020 | 19 590 (16·5) | 399 (22·7) | .. | 4·83 (4·50–5·20) | |
| 2021 | 18 990 (16·2) | 366 (21·3) | .. | 4·48 (4·04–4·98) | |
Data are mean (SD) or n (%), unless otherwise indicated. Population size and age were determined on Jan 1, 2020. HRs are adjusted for age and sex, and compare the population with intellectual disabilities with the general population. Counts less than ten are not shown because of the privacy risk.
Expected deaths are calculated with sex and age group standardised rates from the general population; counts are rounded up to nearest whole and presented with 95% prediction intervals.
Denominators are the totals in the entire group row.
In both the population with intellectual disabilities (460 [60·1%] of 765 people) and the general population (20 826 [54·0%] of 38 580 people) men were overrepresented among COVID-19-related deaths, but the relative risk for COVID-19-related mortality was higher for women with intellectual disabilities (HR 6·16, 95% CI 5·50–6·90) than for men with intellectual disabilities (4·33, 3·94–4·75; table 3). People with intellectual disabilities died at younger ages from COVID-19 than did people in the general population (67·7 years [SD 12·2] vs 81·9 years [9·8]; p<0·0001). Individuals aged 60–69 years at the start of the pandemic (age 55–64 years at enrolment) had most COVID-19-related deaths in the population with intellectual disabilities (252 [32·9%] of 765 people), whereas most COVID-19-related deaths were expected in those aged 70–79 years (65–74 years at enrolment; table 3). The COVID-19-related mortality disparity between the population with intellectual disabilities and the general population was highest at young ages and declined with increasing age (table 3).
Compared with before the pandemic, the death rate during the pandemic increased more in the population with intellectual disabilities (120·7 deaths per 10 000 people per year vs 151·2 deaths per 10 000 people per year) than in the general population (117·1 deaths per 10 000 people per year vs 134·4 deaths per 10 000 people per year), resulting in a higher HR during the pandemic (HR 3·38 95% CI 3·29–3·47) than before the pandemic (3·23, 95% CI 3·17–3·29; table 2). The frequency distribution of deaths from major individual causes within each disease category is included in the appendix (pp 1–2).
For five disease groups (neoplasms; mental, behavioural, and nervous system; circulatory system; external causes; and other natural causes) higher mortality rates were observed in the population with intellectual disabilities during the pandemic than before the pandemic, and the pre-pandemic to during the pandemic difference in mortality rates was greater in the population with intellectual disabilities than in the general population, despite the younger mean age of the population with intellectual disabilities compared to the general population (table 3). However, a significantly higher HR for the population with intellectual disabilities relative to the general population was only observed for external causes (table 3).
Notable changes in specific causes of death in the population with intellectual disabilities included an increase in deaths due to poorly defined cancers (cancer of unknown primary—C80; and unknown or uncertain behaviour—D37–D48), fewer deaths due to pneumonia (J18), more accidental falls (W19), more deaths related to diabetes (E100–E14), and fewer deaths from Down syndrome (Q90; appendix pp 1–2). In both groups, more deaths were coded with R99 (other ill-defined and unspecified causes of mortality) during the pandemic than before.
Discussion
In this study, we analysed mortality patterns among Dutch adults with intellectual disabilities within the first two calendar years (2020 and 2021) of the COVID-19 pandemic and compared them with pre-pandemic patterns. The overall mortality disparity between people with and without intellectual disabilities during the pandemic was wider than before. Mortality due to COVID-19 was almost five times higher than in the general population, and particularly high for young people with intellectual disabilities compared with people in the same age groups in the general population. Disparities for causes of death other than COVID-19 were also further widened, indicating the impact of the COVID-19 pandemic for people with intellectual disabilities has been greater than what is reflected by the number of COVID-19 deaths alone.
Several studies in multiple countries have shown increased mortality risks for people with intellectual disabilities due to COVID-19.24, 33, 34 Intellectual disabilities has even been identified to be one of the largest independent risk factors—besides age—for COVID-19-related mortality in the USA.8 Yet, to our knowledge, our study is one of the first to report these findings across the full first 2-year span of the pandemic with national registry data. This knowledge improves the understanding of the origin of the observed disparities between people with intellectual disabilities and the general population, and the need to address them when designing policies for future pandemics.
During the pandemic, we also observed an increase in deaths among people with intellectual disabilities for causes other than COVID-19, including related to certain types of cancer, diabetes, and accidental falls. Although the available data do not provide information about the context and circumstances at the time of death, these findings could indicate a reduction in the provision of routine care and increased barriers to receiving adequate health care during the pandemic for people with intellectual disabilities. Moreover, COVID-19 might have interfered with pre-existing health problems and, thus, indirectly affected deaths from competing causes. To investigate these pathways, linkage between COVID-19 test results and medical records needs to be done, which is not yet possible in the Netherlands. Similarly, the decline in some other causes of death during the pandemic, such as respiratory or congenital diseases (eg, Down syndrome), is likely to be explained by the fact that those at high risk of dying from these causes were also at a high risk of dying from COVID-19. During the pandemic, this mechanism might have even reduced the phenomenon of miscoding deaths in populations with intellectual disabilities, where intellectual disability or Down syndrome is incorrectly listed as the underlying cause of death in circumstances where the actual cause is not readily apparent.35, 36
This study has two important implications. First, the study underlines the need for attention in public health policies and clinical practice for the vulnerability of people with disabilities. Availability of more and better-quality routine data about people with disabilities might have improved disability-inclusive communication and availability of personal protective measures in disability care during the COVID-19 pandemic. From a broader perspective, better-quality data can provide evidence for decision making, policies, and development of guidelines.37, 38, 39 Second, there is a clear need for improved infrastructure for the public health monitoring of high-risk groups. Monitoring COVID-19-related mortality is part of population surveillance in the Netherlands, as in many other countries. However, the disproportionate effect of the pandemic on people with intellectual disabilities only became visible after databases were linked for this study and, thus, in retrospect. Alternative registries have been developed, also in the Netherlands, but were often restricted in timeperiod, outcomes, or study sample.15 Although real-time data were unavailable to inform the public health response, this alternative registry provided the evidence needed to prioritise people with intellectual disabilities for COVID-19 vaccination in the Netherlands.15 As many decisions in public health are data driven, a disability-inclusive data infrastructure is required for more timely insights and a quicker response towards those in need of action.37, 38 Mortality data are among the best available sources of public health information for such an approach, as they provide information about current health problems, including preventable and treatable causes, suggest persistent patterns of disparities in specific populations, and show trends over time. An example of a tailored monitoring programme is the Learning (Intellectual) Disabilities Mortality Review programme in England.3, 40 Lessons from this programme could contribute to service improvements locally and nationally, but also show the need for specific attention from policy and research, and a dedicated infrastructure.
A major strength of this study is the population coverage, with information on demographics, disability status, and mortality. For all registered deaths, a cause was submitted, although that reason could be labelled as unknown or unspecified, mostly coded as “other ill-defined and unspecified deaths (R99)”, which appeared more frequently in both our study groups during the COVID-19 pandemic than before the pandemic. Increased workload during the pandemic might have caused an increase in erroneous death certificates being submitted. Potentially, some of these deaths could also have been unidentified COVID-19 cases; this is especially likely in the first months of 2020, when testing capacities were constrained. However, the overall impact of unknown or unspecified coding on outcomes is small; although the proportion of unknown or unspecified causes of deaths was increased, as part of the total number of deaths the proportion was low.
Information about disability status was limited by the fact that it was obtained from secondary sources from Dutch national long-term care and social services, and provided no information about intellectual disability causes, as such information is unavailable in any Dutch population database. Yet, the information available represents the most comprehensive population-based database on intellectual disability available in the Netherlands, and the intellectual disability prevalence determined in this database aligned with international prevalence estimates.4, 5, 27 Furthermore, accurate classification of intellectual disabilities was supported by the fact that intellectual disability-specific causes of death almost exclusively appeared in the population with intellectual disabilities. This indiciates that despite people with intellectual disabilities in this study being identified through systems exclusive to the Netherlands, groups of similar individuals would be identified in other countries with different health systems and social services. A further limitation is that the applied participant identifcation method provided no information about ethnicity or other sociodemographic characteristics that might have interacted with the outcomes in this study.
In conclusion, COVID-19 disproportionally affected people with intellectual disabilities, but the impact of the pandemic was larger than shown by COVID-19 deaths alone. With an increase in deaths from causes other than COVID-19, existing mortality disparities between the population with intellectual disabilities and the general population were further widened. The health risks for people with intellectual disabilities warrant targeted policy making regarding protective measures for current and future pandemics, and critical evaluation of the access for these individuals to health care in general. For this purpose, better infrastructure for disability-inclusive public health data is needed.
Data sharing
Aggregated data from the databases used in this study are publicly available on a dedicated website of Statistics Netherlands (https://statline.cbs.nl). The non-public microdata used to link databases are, under certain conditions, accessible for statistical and scientific research (fees apply). Procedures to request access can be found at https://https://www.cbs.nl, and for further information contact microdata@cbs.nl. Aggregated data and analytical code are available on request to the corresponding author.
Declaration of interests
We declare no competing interests.
Acknowledgments
Acknowledgments
This study was supported by a grant from the Dutch Ministry of Health, Welfare, and Sport (grant number 329574) and a grant from the Netherlands Organization for Health Research and Development (grant number 641001100).
Contributors
All authors conceived the study and contributed to the design and statistical approach. JN and GLL supervised the study. MC and MCJK-L had full access to the data, which were located within a secure digital research environment at Statistics Netherlands, verified the underlying data, and conducted analyses. BWMS had viewing rights in this digital environment, provided methodological input on the analyses, and verified the reported data. EJB-vG, JN, and GLL had access to (aggregated) results. All authors contributed to interpretation of the results. MC, MCJK-L, BWMS, and JN wrote the original draft, which was reviewed and edited by GLL and EJB-vG. All authors approved the final manuscript and accept responsibility for the decision to submit for publication.
Supplementary Material
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Aggregated data from the databases used in this study are publicly available on a dedicated website of Statistics Netherlands (https://statline.cbs.nl). The non-public microdata used to link databases are, under certain conditions, accessible for statistical and scientific research (fees apply). Procedures to request access can be found at https://https://www.cbs.nl, and for further information contact microdata@cbs.nl. Aggregated data and analytical code are available on request to the corresponding author.