Introduction

Colorectal cancer is the third most common cancer diagnosed in Canada and the second and third leading cause of cancer deaths among Canadian men and women, respectively [1]. Removal of adenomatous polyps has been shown to reduce its incidence by 76% to 90% [2]; colorectal cancer therefore presents an ideal target for early detection and prevention through screening [3]. Several screening tests are available, including flexible sigmoidoscopy, colonoscopy, the fecal occult blood test (FOBT), and, more recently, the fecal immunochemical test.

In 2008, the province of Ontario instituted the first population-based colorectal cancer screening program in Canada. The program’s goals are to increase the capacity of primary care to participate in organized colorectal cancer screening and to reduce mortality from colorectal cancer. At the time of this writing, biennial screening using the guaiac fecal occult blood test (FOBT) is recommended for individuals 50 to 74 years of age at average risk of colorectal cancer, followed by colonoscopy for those with an abnormal FOBT. For persons at increased risk because of a family history of the disease, colonoscopy is recommended beginning at age 50, or 10 years earlier than the age at which a first-degree relative was diagnosed with colorectal cancer, whichever occurs first [4].

Our group received funding from the Canadian Institutes of Health Research in 2010 to address the need for more comprehensive data to support decision-making, policy development, service provision, and research relevant to the health and well-being of Ontarians with developmental disabilities (henceforth referred to as intellectual and developmental disabilities, or IDD; under Ontario’s Services and Supports to Promote the Social Inclusion of Persons with Developmental Disabilities Act (2008), “developmental disability” is an umbrella term that includes conditions such as intellectual disability, autism spectrum disorder, and fetal alcohol spectrum disorder). Part of that work involved evaluating the extent to which the Ontario health system provides guideline-recommended primary care to adults with IDD, including preventive screening for various cancers.

While several studies have reported lower rates of breast [5,6] and cervical cancer screening [5–7] among women with intellectual and/or developmental disabilities, we are not aware of any studies that have examined participation in colorectal cancer screening among adults with IDD. As their life expectancy increases [8,9], suboptimal screening practices may contribute to a greater cancer burden in this population [10]. Our objectives, therefore, were to determine the proportion of Ontarians with IDD who have been screened for colorectal cancer; to compare their screening participation rates to those of Ontarians without IDD; and to explore whether certain sociodemographic and health care utilization characteristics are associated with screening uptake among Ontarians with IDD. In addition to providing data on an understudied issue that is important from a health care and health equity perspective, our findings will provide a baseline for monitoring trends in screening uptake among individuals with IDD, particularly as they relate to the implementation of measures to increase Ontarians’ participation in the province’s colorectal cancer screening program (discussed further on under Ontario’s ColonCancerCheck Program).

Methods

Ethics approval to conduct this study was obtained from research ethics boards at Sunnybrook Health Sciences Centre and the Centre for Addiction and Mental Health (both in Toronto, Canada). Informed consent was not sought as only de-identified data (housed at Ontario’s Institute for Clinical Evaluative Sciences) were analyzed.

Results

Table 1 provides the sociodemographic and health care utilization characteristics of the study cohort stratified by IDD status, and the proportions who 1) had an FOBT in the previous two years, and 2) were up-to-date with colorectal tests as of March 31, 2010. Compared to those without IDD, proportionally more individuals with IDD were 50–59 years of age and male, lived in rural or low-income areas, and were characterized as having high or very high morbidity (i.e. greater expected use of health care resources). Fewer were enrolled with or seeing a physician in a primary care patient enrolment model. Overall, 18.3% of Ontarians with IDD had an FOBT in the previous two years and 32.0% were up-to-date with colorectal tests; the corresponding proportions for those without IDD were 26.4% and 47.2%, respectively (Table 2). After controlling for the other study variables, the odds of having had an FOBT in the previous two years were 32% lower for Ontarians with IDD; similarly, their odds of being up-to-date with colorectal tests were about half those of Ontarians without IDD (Table 2).

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Table 1. Sociodemographic and health care utilization characteristics of Ontarians 50–64 years of age with and without intellectual and developmental disabilities, and proportions who participated in colorectal cancer screening.

https://doi.org/10.1371/journal.pone.0118023.t001

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Table 2. Odds ratios for uptake of colorectal cancer screening among Ontarians 50–64 years of age with intellectual and developmental disabilities.

https://doi.org/10.1371/journal.pone.0118023.t002

Table 3 provides unadjusted and adjusted odds ratios for the sociodemographic and health care utilization characteristics of the population with IDD in relation to having had an FOBT in the previous two years. Older individuals, women, those in any resource utilization band above the reference category of “Non-users,” and those enrolled with or seeing a physician in a patient enrolment model were significantly more likely to have had an FOBT. Living in an urban area was not significantly associated with FOBT participation in this population. Similar results were observed for the association between these same characteristics and being up-to-date with colorectal tests (Table 4).

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Table 3. Frequency distributions and odds ratios for having had a fecal occult blood test in previous two years among Ontarians 50–64 years of age with intellectual and developmental disabilities, by sociodemographic and health care utilization characteristics.

https://doi.org/10.1371/journal.pone.0118023.t003

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Table 4. Frequency distributions and odds ratios for being up-to-date with colorectal tests as of March 31, 2010 among Ontarians 50–64 years of age with intellectual and developmental disabilities, by sociodemographic and health care utilization characteristics.

https://doi.org/10.1371/journal.pone.0118023.t004

Certain strata of neighbourhood income had a weak but significant association with screening uptake. Ontarians with IDD from neighbourhoods that fell in the middle income quintile were more likely to have had an FOBT than those living in the poorest neighbourhoods, while those living in the highest or middle income quintiles were significantly more likely to be up-to-date with colorectal tests compared to those in the poorest neighbourhoods.

Discussion

The absolute difference between the proportions of Ontarians with and without IDD who had an FOBT in the previous two years was 8.1% (Table 2). While this is less of a disparity than the differences observed between these groups in terms of cervical and breast cancer screening uptake (32.5% and 18.3%, respectively [5]), that may be due to the low participation in colorectal cancer screening overall: only 26.3% of the study cohort had an FOBT in the previous two years (data not shown in tabular format). The absolute difference between the groups in the “up-to-date with colorectal tests” indicator was larger, at 15.2% (Table 2). While these absolute differences do not take into account the unequal distribution between the groups of characteristics that may be associated with screening participation (e.g. age, sex; Table 1), Ontarians with IDD were still significantly less likely to have participated in colorectal cancer screening after controlling for various sociodemographic and health care utilization characteristics (Table 2).

The term “equity” encompasses notions of fairness and social justice [25]. When a disparity in health care exists among groups with equal needs—in the case of colorectal cancer screening, “need” at a population level is based on age—it indicates a lack of horizontal equity [21]. Our findings, then, reveal a horizontal inequity in access to colorectal cancer screening among Ontarians with IDD. Moreover, significant disparities in screening uptake were also observed within subgroups of the IDD population, in that older individuals, women, those who were categorized in a resource utilization band above “Non-users,” and those enrolled with or seeing a physician in a primary care patient enrolment model were more likely to have been screened (Tables 3 and 4). In contrast, while one study reported that Ontarians living in rural areas were less likely to have been screened for colorectal cancer than urban residents [18], this was not a significant predictor of screening uptake in the IDD population (Tables 3 and 4). The findings for neighbourhood income are more difficult to interpret: some of the results were significant, but there was no clear linear gradient when moving from lower- to higher-income neighbourhoods (Tables 3 and 4). Most of these findings are similar to the patterns observed in the unadjusted proportions for those without IDD (Table 1).

As previously noted, the ColonCancerCheck Program has launched an invitation system in an effort to increase screening uptake among age-eligible Ontarians [4]. Whether that will have any impact on individuals with IDD is unknown; a 2009 report issued by Cancer Care Ontario noted that client reminders are an effective population-based intervention to increase uptake of breast, cervical and colorectal cancer screening, but also acknowledged the lack of evidence on the effectiveness of interventions for different population groups [26].

In order to implement interventions that effectively address inequities in colorectal cancer screening—between those with and without IDD, and among subgroups of both populations—it is crucial to first identify the barriers to, and facilitators of, access to screening. A review article published in 2010 identified a number of patient and system barriers and facilitators [21]. While some of these (e.g. embarrassment) may apply across population groups, individuals with IDD face unique barriers [10,27]. In the case of colorectal cancer screening, the FOBT requires at-home collection of two specimens each from three separate stools. (Note that a pilot project is now underway in Ontario to investigate the feasibility of replacing the FOBT with the fecal immunochemical test; the latter has been found to increase screening participation rates, likely because it requires fewer samples and the collection method is simpler [28].) Most adults with IDD will need to rely on others to support them in these tasks. Thus, caregivers’ attitudes, knowledge and skills need to be examined in terms of their potential role in facilitating colorectal cancer screening among individuals with IDD.

That same review reported that lack of physician recommendation is the primary system barrier to colorectal cancer screening [21]. Our study was not designed to determine the barriers to, and facilitators of, access to colorectal cancer screening among persons with IDD. Given the design of Ontario’s colorectal cancer screening program (described earlier under Ontario’s ColonCancerCheck Program), however, it seems reasonable to assume that the supply side plays a key role in screening uptake. Some of our findings indirectly support this. For example, we observed a strong association between higher morbidity/expected use of health care resources and participation in colorectal cancer screening (albeit without a consistent linear gradient for FOBT participation; see Table 3), which suggests that physicians engage in opportunistic screening of individuals who have greater contact with the health care system. Moreover, being enrolled with or seeing a physician in a primary care patient enrolment model was positively associated with screening participation among Ontarians with IDD (Tables 3 and 4). We could not determine, from the data available, which characteristics of patient enrolment models promote screening, but one hypothesis relates to financial incentives: an increase in screening uptake was observed prior to the 2008 launch of the ColonCancerCheck Program, which may have been at least partly attributable to the province’s introduction in 2006 of financial incentives for colorectal cancer screening [18]. As stated earlier, physicians in patient enrolment models receive greater financial incentives to conduct colorectal cancer screening than physicians who practice under the traditional fee-for-service model [15].

The preceding two paragraphs allude to the potentially important role caregivers and physicians play in colorectal cancer screening uptake among individuals with IDD. From that perspective, it might be useful to evaluate caregivers’ and physicians’ knowledge regarding colorectal cancer risk in this population. Individuals with Down syndrome—one of the most common known causes of intellectual disability [29]—have a lower risk of solid tumours [30], including colorectal cancer [31], than the general population. That fact may influence beliefs about colorectal cancer risk among the broader population of individuals with IDD, and hence their need for screening. Caregivers and physicians need to be aware that those with Down syndrome constitute a unique group within the IDD population [31], and that women with intellectual disabilities may actually be at increased risk of colorectal cancer compared to women in the general population [32].

As previously noted, in Ontario colonoscopy is the recommended screening procedure only for those at increased risk of colorectal cancer. In other jurisdictions, it is more commonly used for screening purposes [33]. Some individuals with IDD require sedation for minor surgery, which could present an opportunity to perform a screening colonoscopy, depending on the facility and degree of coordination and cooperation among providers [27]. However, colonoscopies present some risks and require complete cleansing of the colon. One American study reported a high rate (46%) of inadequate preparation for the procedure among individuals with IDD [31]. Thus, it is unclear whether colonoscopy could form a viable first-line screening tool to increase screening uptake among adults with IDD. If Ontario does adopt the fecal immunochemical test for colorectal cancer screening, that test’s simpler collection method may increase screening uptake in the IDD population (and with the baseline data generated by the current study, we will be able to evaluate whether this is the case in a future analysis).

A notable strength of this study is the province-wide coverage of the data sources used. For this reason, and because the OHIP Database captures fee-for-service claims and shadow billings as well as claims for FOBTs processed in laboratories (excluding specimens processed in hospitals), it is likely we were able to identify most of the age-eligible population who have been screened. Moreover, the use of administrative data may be a more accurate method of measuring screening uptake compared to surveys, as certain groups may over-report participation in cancer screening [34]. Nevertheless, we acknowledge certain limitations related to the measurement of screening uptake: a small proportion of FOBTs may have been done for diagnostic rather than screening purposes [4,18], and we could not identify and exclude those from the analysis; FOBTs analyzed in hospital laboratories would not have been captured [4,18]; some of those captured may have included kits that were rejected at the time of testing [4,18]; we were unable to identify individuals at increased risk of colorectal cancer and exclude them from the analysis; and a small number of colonoscopies may not have been captured in the administrative data [4].

A further limitation is that not all variables that are potentially important in terms of screening uptake are captured in the administrative datasets we used. These include factors such as ethnicity and individual measures of socioeconomic status [21]. Living arrangements (e.g. group home, independent living) could also be an important determinant of screening participation among individuals with IDD, but that information was not available in the data sources. Moreover, identifying individuals with IDD is a recognized challenge for researchers [35]. In this study, IDD status was defined based on the presence of ICD-9 and ICD-10 diagnostic codes in administrative datasets, and those administrative diagnoses have not been validated using a clinical reference standard. Furthermore, it is likely that administrative data fail to identify the entire population of individuals with IDD [36,37]. If some individuals were misclassified as “non-IDD” in our cohort, and if they have similar screening participation rates to those who were accurately classified as having IDD, it could mean that disparities in screening uptake may be even larger than reported here.

As a final note, this study focused on participation in the initial stage of colorectal cancer screening. However, equal access to all components of the screening process is necessary to achieve true equity in health care. Those other components include follow-up evaluation in the case of a positive screening test result and subsequent treatment, if warranted. A lack of availability and access to data is an acknowledged difficulty in tracking inequities across the entire screening process [21].

Conclusion

Even in systems that provide universal access to health care, certain groups encounter barriers that hinder their utilization of services [21]. Equity of access to colorectal cancer screening programs has been studied in various population groups, including those defined by socioeconomic status and ethnicity (reviewed by Javanparast et al., 2010 [21]), but, to our knowledge, this is the first study to examine this issue in adults with IDD. The Canadian Consensus Guidelines on the Primary Care of Adults with Developmental Disabilities recommends regular screening for colorectal cancer in adults older than 50 years [38]. Despite this recommendation, our findings reveal low uptake of colorectal cancer screening among Ontarians with IDD. While similar sociodemographic and health care utilization characteristics appeared to be associated with screening participation among individuals with and without IDD in our study, there are likely reasons for lower uptake that are unique to the former group. This underscores the need to identify the barriers to and facilitators of colorectal cancer screening among individuals with IDD, and to develop effective interventions to increase screening uptake in this population.

Acknowledgments

The authors gratefully acknowledge the contribution of the following Health Care Access Research and Developmental Disabilities (H-CARDD) Program investigators to the design of this study: Yona Lunsky, Robert Balogh, Elizabeth Lin, and Barry Isaacs.