Development and validation of the Crohn's disease perceived work disability questionnaire

Patient-Reported Outcomes in Inflammatory Bowel Disease: A Measurement of Effect in Research and Clinical Care

The measurement of outcomes is key in evaluating healthcare or research interventions in inflammatory bowel disease (IBD). In patient-centred care, patient-reported outcome measures (PROMs) are central to this evaluation. In this review, we provide an overview of validated, adult disease-specific PROMs developed for use in IBD. Our aim is to assist clinicians and researchers in selection of PROMs to measure outcomes in their patient cohort. The Consensus-based Standards for the Selection of Health Measurement Instruments database of systematic reviews was the primary resource used to identify PROMs used in IBD. Search terms were ‘Crohn’s disease’, ‘ulcerative colitis’, and ‘IBD’. Seven systematic reviews were identified from this search. In addition, the publication by the IBD Core Outcome Set Working Group was used to identify further PROMs. Three systematic reviews were excluded as they did not meet the inclusion criteria. From the five included systematic reviews, we identified 21 PROMs and their shortened versions. In conclusion, it does not appear that any one PROM is entirely suitable for both research and clinical practice. Overall, the IBDQ-32 is most widely used in research but has the limitation of cost, whereas the IBD-Control has been recommended in the clinical core outcome set.

Systematic Review of Development and Content Validity of Patient-reported Outcome Measures in Inflammatory Bowel Disease: Do We Measure What We Measure?

BACKGROUND AND AIMS

Patient-reported outcome measures are increasingly important in daily care and research in inflammatory bowel disease [IBD]. This study provides an overview of the content and content validity of IBD-specific patient-reported outcome measures on three selected constructs.

METHODS

Databases were searched up to May 2019 for development and/or content validity studies on IBD-specific self-report measures on health-related quality of life, disability, and self-report disease activity in adults. Evidence was synthesised on content validity in three aspects: relevance, comprehensiveness, and comprehensibility following the COnsensus-based Standards for the selection of health Measurement INstruments methodology. Questionnaire items were organised in themes to provide an overview of important aspects of these constructs.

RESULTS

For 14/44 instruments, 25 content validity studies were identified and 25/44 measures had sufficient content validity, the strongest evidence being of moderate quality, though most evidence is of low or very low quality. The Crohn's Life Impact Questionnaire and IBD questionnaire-32 on quality of life, the IBD-Control on disease activity, and the IBD Disability Index Self-Report and its 8-item version on disability, have the strongest evidence of sufficient relevance, comprehensiveness, and comprehensibility, ranging from moderate to very low quality. A fair number of recurring items themes, possibly important for the selected constructs, was identified.

CONCLUSIONS

The body of evidence for content validity of IBD-specific health-related quality of life, self-report disease activity, and disability self-report measures is limited. More content validity studies should be performed after reaching consensus on the constructs of interest for IBD, and studies should involve patients.

Validation of a self-reported work disability questionnaire for ulcerative colitis

Ulcerative colitis (UC) may severely limit patients' capacity to work. Recently, we validated a work disability questionnaire (WDQ) for Crohn disease. As UC shares clinical characteristics with Crohn disease, we hypothesized that the questionnaire might also be useful for UC. The study was aimed to validate the WDQ for use in UC.Consecutive patients with UC (n = 142, 67 women; age 48 ± 1) completed the UC-WDQ and the inflammatory bowel disease questionnaire-9 (IBDQ-9), and EuroQoL-5D quality-of-life questionnaires. Validation of the UC-WDQ included an assessment of its construct validity, including: discriminant validity, convergent validity, and reproducibility (test-retest). We also calculated the intraclass correlation and the Cronbach alpha.The UC-WDQ is a valid and reliable tool for measuring work disability in patients with UC.

Workability for persons with chronic diseases. A systematic review of validity and utility of assessments in German language / Valide und praktikable deutschsprachige Assessments zur Erfassung der Arbeitsfähigkeit bei Menschen mit chronischen Erkrankungen – eine systematische Review

Background

People with chronic diseases are often limited in their workability. Evaluating and enabling workability is central in rehabilitation. The aim of this study was to evaluate validity and utility of workability assessments in German for persons with chronic diseases.

Methods

The study is a systematic review. First, we systematically searched for literature in the databases Medline, CINAHL, PsycInfo, Cochrane HTA Database, DARE, CCMed, Sowiport, and BASE using following keywords: evaluation tool, chronic disease, workability, validity, and utility. Then, we evaluated the content and the quality of the studies based on criteria and decided if they were included.

Results

In total, validity and utility of eight workability assessments are described based on 74 studies. The assessments are: Productivity Costs Questionnaire (iPCQ), Work Instability Scale for Rheumatoid Arthritis (RA-WIS), Screening-Instrument Arbeit und Beruf (SIBAR), Screening-Instrument zur Feststellung des Bedarfs an medizinisch-beruflich orientierten Maßnahmen in der medizinischen Rehabilitation (SIMBO), Valuation of Lost Productivity Questionnaire (VOLP), Work Ability Index (WAI/ABI), Work Limitations Questionnaire (WLQ), and Work Productivity and Activity Impairment Questionnaire (WPAI).

Conclusion

The results revealed the availability of eight workability assessments for persons with chronic diseases in German language. They have strengths and weaknesses in relation to the construct, purpose, application, and evidence base. These could be the base for choice of an assessment. Overall, we suggest using workability assessment in order to meet the legal requirements for the use of standardized assessments and the increasing demand to establish evidence of the effectiveness of interventions.

Validation of the Inflammatory Bowel Disease Disability Index in a population-based cohort

BACKGROUND

IBDs are chronic destructive disorders that negatively affect the functional status of patients. Recently, the Inflammatory Bowel Disease Disability Index (IBD-DI) was developed according to standard WHO processes. The aims of the current study were to validate the IBD-DI in an independent patient cohort, to develop an index-specific scoring system and to describe the disability status of a well-defined population-based cohort of French patients with IBD.

METHODS

From February 2012 to March 2014, the IBD-DI questionnaire was administered to a random sample of adult patients with an established diagnosis of IBD issued from a French population-based registry. The IBD-DI consists of 28 items that evaluate the four domains of body functions, activity participation, body structures and environmental factors. Validation included item reduction and data structure, construct validity, internal consistency, interobserver and intraobserver reliability evaluations.

RESULTS

150 patients with Crohn's disease (CD) and 50 patients with UC completed the IBD-DI validation phase. The intraclass correlation coefficient for interobserver reliability was 0.91 and 0.54 for intraobserver reliability. Cronbach's α of internal consistency was 0.86. IBD-DI scores varied from 0 to 100 with a mean of 35.3 (Q1=19.6; Q3=51.8). IBD-DI scores were highly correlated with Inflammatory Bowel Disease Questionnaire (-0.82; p<0.001) and SF-36 (-0.61; p<0.05) scores. Female gender (p<0.001), clinical disease activity (p<0.0001) and disease duration (p=0.02) were associated with higher IBD-DI scores.

CONCLUSIONS

The IBD-DI has been validated for use in clinical trials and epidemiological studies. The IBD-DI showed high internal consistency, interobserver reliability and construct validity, and a moderate intraobserver reliability. It comprises 14 questions and ranges from 0 to 100. The mean IBD-DI score was 35.3 and was associated with gender, clinical disease activity and disease duration. Further research is needed to confirm the structural validity and to assess the responsiveness of IBD-DI.

TRIAL REGISTRATION NUMBER

2011-A00877-34.

Employment status, difficulties at work and quality of life in inflammatory bowel disease patients

OBJECTIVES

To assess employment status, difficulties at work and sick leave in inflammatory bowel disease (IBD) patients and their relation with sociodemographic and clinical factors, quality of life (QoL), and anxiety and depression.

MATERIALS AND METHODS

IBD patients attending an IBD outpatients' clinic received self-report questionnaires on employment status, IBD-related difficulties at work and sick leave (Trimbos/iMTA questionnaire for Costs associated with Psychiatric Illness), sociodemographic factors, QoL (Inflammatory Bowel Disease Questionnaire and 12-item Short-form Health Survey) and anxiety and depression (Hospital Anxiety and Depression Scale). Disease activity was assessed by their gastroenterologist. Associations between paid employment and sick leave with sociodemographic and clinical factors, QoL and anxiety and depression were assessed by regression analyses.

RESULTS

In total, 202 IBD patients of working age, with a mean age of 41 years, participated; 63% had Crohn's disease and 37% had ulcerative colitis, and 57% were women and 19% had active disease. In all, 123 (61%) patients were in paid employment, of whom 31 (25%) were on sick leave, whereas 46 (23%) received a disability pension. Concentration problems (72%), low working pace (78%) and delayed work production (50%) were the most prevalent IBD-related work difficulties. IBD patients without paid employment were older and more often women, with active disease, lower QoL and higher anxiety and depression rates. Sick leave was associated with lower QoL and higher anxiety and depression rates.

CONCLUSION

More than half of IBD patients were in paid employment, whereas almost a quarter was receiving a disability pension. A large majority experienced work difficulties. Having no paid employment was associated with poorer QoL and more anxiety and depression symptomatology.

Development and Validation of the Short Crohn's Disease Work Disability Questionnaire

BACKGROUND

The aim was to develop and validate a self-reported short Crohn's disease work disability questionnaire (sCDWDQ).

METHODS

(1) Development of a shortened questionnaire-Patients' responses to the validation process (n = 108) of a previously developed, 16-item Spanish Crohn's disease work disability questionnaire (CDWDQ) were analyzed using the Rasch model for multiple response items. After this process, a 9-item sCDWDQ was obtained. (2) Validation phase-The validation assessed the questionnaire's convergent validity, discriminant validity, test-retest reproducibility, and internal consistency. Spearman rank correlation, t test, intra-class correlation and Cronbach's alpha were used for the analysis.

RESULTS

One hundred fifty-one patients were included in the validation phase. (1) Convergent validity was confirmed by correlations between the sCDWDQ and clinical activity (r = 0.66, P < 0.01), the short inflammatory bowel disease questionnaire IBDQ-9 (r = 0.74, P < 0.001), Euroqol-5D (r = 0.63, P < 0.01), the EuroQol-5D visual analog scale (r = 0.54, P < 0.01), and overall work impairment (r = 0.66, P < 0.01); (2) Discriminant validity-sCDWDQ scores were higher in patients with active disease (20.1 ± 6.3 versus 13.0 ± 3.8 inactive, P < 0.001), in those requiring previous sick leave (19.6 ± 6.9 versus no sick leave 14.2 ± 4.8, P < 0.01) and in those requiring hospitalization (20.0 ± 7.3 [n = 29] versus no hospitalization 14.1 ± 7.3 [n = 90], P < 0.01); (3) Internal consistency was also good (Cronbach's alpha = 0.92); and (4) Reproducibility-sCDWDQ measures obtained 2 weeks apart showed an excellent intraclass correlation coefficient of 0.92 (95% confidence interval, 0.90-0.94).

CONCLUSIONS

The self-reported sCDWDQ appears to be a simple, valid, and reliable tool for measuring work disability in Crohn's disease.

Development of a conceptual model evaluating the humanistic and economic burden of Crohn's disease: implications for patient-reported outcomes measurement and economic evaluation

The primary objective of this review is to develop a conceptual model for Crohn's disease (CD) outlining the disease burden for patients, healthcare systems and wider society, as reported in the scientific literature. A search was conducted using MEDLINE, PsycINFO, EconLit, Health Economic Evaluation Database and Centre for Reviews and Dissemination databases. Patient-reported outcome (PRO) measures widely used in CD were reviewed according to the US FDA PRO Guidance for Industry. The resulting conceptual model highlights the characterization of CD by gastrointestinal disturbances, extra-intestinal and systemic symptoms. These symptoms impact physical functioning, ability to complete daily activities, emotional wellbeing, social functioning, sexual functioning and ability to work. Gaps in conceptual coverage and evidence of reliability and validity for some PRO measures were noted. Review findings also highlight the substantial direct and indirect costs associated with CD. Evidence from the literature confirms the substantial burden of CD to patients and wider society; however, future research is still needed to further understand burden from the perspective of patients and to accurately understand the economic burden of disease. Challenges with existing PRO measures also suggest the need for future research to refine or develop new measures.

Impact of inflammatory bowel disease on disability

Inflammatory bowel disease can impact individuals at a young age, thus compromising their work productivity. Besides the inability to engage in gainful work, the concept of disability also relates to the patients' diminished ability to undertake household and social activities. A literature search was performed of recent literature, and all articles containing information about the impact of inflammatory bowel disease on disability or any work-related outcomes were included. Recent studies suggest that 9 to 19% of inflammatory bowel disease patients suffer from short-term absences from work and 19 to 22% are on long-term disability. Crohn's disease patients reported being more affected by their disease than ulcerative colitis patients. A comparison of results from different studies is difficult due to the lack of consensus on how to define and measure disability. Additional research is needed to better quantify disability in inflammatory bowel disease patients.

Systematic review of health-related quality of life measures for inflammatory bowel disease

BACKGROUND AND AIM

Several measures have been developed to assess the health-related quality of life [HRQoL] of patients with inflammatory bowel disease [IBD]. Our aim is to systematically review the HRQoL measures specific for patients with IBD and to appraise their measurement properties and methodological quality.

METHODS

We searched the PubMed, Embase, and PsycINFO databases for original articles describing the development and/or evaluation of one or more of the measurement properties [e.g. internal consistency, reliability, validity, responsiveness] of HRQoL measures specific for IBD. We assessed the measurement properties and examined the methodological quality of the measurement properties of each instrument using a standardized checklist.

RESULTS

We examined the full text of 75 articles that we deemed potentially eligible and identified 10 disease-specific HRQoL measures in IBD that covered different aspects of patients' lives. Internal consistency, construct validity, and content validity were the commonly evaluated measurement properties. Seven HRQoL measures scored positive for at least four of eight measurement properties. The majority of studies were rated as 'fair' to 'poor' when assessing their methodology quality. The most established HRQoL measure in the literature was the Inflammatory Bowel Disease Questionnaire [IBDQ].

CONCLUSIONS

Most of the included HRQoL measures did not include all the required measurement properties or had a problem with their methodological quality. The most widely used and validated measure was the IBDQ. Further validation studies are required to support the use of other HRQoL measures.

Development of a short questionnaire to assess the quality of life in Crohn's disease and ulcerative colitis

BACKGROUND AND AIMS

Most of the disease-specific quality of life (QoL) measures for inflammatory bowel disease (IBD) are lengthy and time consuming. None have been established for routine use in clinical practice. We designed this study to develop a short QoL measure in IBD.

METHODS

A 32-item questionnaire, the Crohn's and ulcerative colitis questionnaire (CUCQ)-32 was developed by reviewing the literature of the previously validated questionnaires and by consultation with patients and experts. Construct validity was carried out using the Short Form 12 and the EuroQol 5 dimensions questionnaires and two disease severity measures (the Simple Clinical Colitis Activity Index and the Harvey-Bradshaw Index). Test-retest analysis was done by asking patients to complete the CUCQ questionnaire twice within a period of two weeks.

RESULTS

Data were obtained from 205 patients with IBD who completed the CUCQ-32. Psychometric analysis showed that Cronbach's α was 0.88, item-total correlations were good, and there were no ceiling or flooring effects. Stepwise regression identified eight items that accounted for >95% of the variance in the CUCQ-32. The resulting CUCQ-8 demonstrated good internal consistency (Cronbach's α = 0.84), had good reproducibility (intraclass correlation coefficient = 0.94), was well correlated with the EuroQol 5 dimensions questionnaire (r = 0.58) and the Short Form-12 (r = 0.65 for physical component and r = 0.63 for mental component), and was responsive to change (responsiveness ratio was 0.64, p-value < 0.05).

CONCLUSIONS

CUCQ-8 is a short questionnaire that has the potential to be an efficient tool for assessing the QoL of all patients with IBD in clinical practice.

Sick leave and disability pension in inflammatory bowel disease: a systematic review

BACKGROUND & AIMS

Inflammatory bowel disease has considerable effects on work-related outcomes and leads to high societal costs due to sick leave and disability pension. The aims of this study were to systematically review evidence on work-related outcomes that are relevant to productivity losses and to evaluate whether medical or surgical interventions have a positive impact on patients' work ability.

METHODS

A systematic literature search in PubMed was conducted in June 2013. Abstracts were screened by two independent reviewers, and full-text articles describing the frequency of work-related outcomes were retrieved. Two independent reviewers extracted data according to the PRISMA Statement for Reporting Systematic Reviews and Meta-Analyses. Findings were organized by study design (non-interventional/interventional). Non-interventional studies were structured according to whether they presented data in comparison to control groups or not and interventional studies were summarized according to type of intervention.

RESULTS

This review included 30 non-interventional (15 with comparison groups and 15 without comparison group) and 17 interventional studies (9 surgical and 8 medical). The majority of the studies reported a high burden of work-related outcomes among inflammatory bowel disease patients regardless of the methodology used. While biologic agents showed positive effect on work absenteeism and presenteeism in randomized clinical trials, the impact of surgical interventions needs further evaluation.

CONCLUSIONS

Inflammatory bowel disease patients experience a high burden in work-related outcomes. Additional data on productivity losses and the long-term impact of interventions is needed to help inform decision-makers about treatment options and their benefits in reducing productivity losses in inflammatory bowel disease patients.

Patient-reported outcomes as primary end points in clinical trials of inflammatory bowel disease

The Food and Drug Administration (FDA) is moving from the Crohn's Disease Activity Index to patient-reported outcomes (PROs) and objective measures of disease, such as findings from endoscopy. PROs will become an important aspect of assessing activity of inflammatory bowel disease (IBD) and for labeling specific drugs for this disease. PROs always have been considered in the management of patients with rheumatoid arthritis or multiple sclerosis, and have included measurements of quality of life, disability, or fatigue. Several disease-specific scales have been developed to assess these PROs and commonly are used in clinical trials. Outcomes reported by patients in clinical trials of IBD initially focused on quality of life, measured by the Short-Form 36 questionnaire or disease-specific scales such as the Inflammatory Bowel Disease Questionnaire or its shorter version. Recently considered factors include fatigue, depression and anxiety, and work productivity, as measured by the Functional Assessment Chronic Illness Therapy-Fatigue, the Hospital Anxiety Depression, and the Work Productivity Activity Impairment Questionnaire, respectively. However, few data are available on how treatment affects these factors in patients with IBD. Although disability generally is recognized in patients with IBD, it is not measured. The international IBD disability index currently is being validated. None of the PROs currently used in IBD were developed according to FDA guidance for PRO development. PROs will be a major primary end point of future trials. FDA guidance is needed to develop additional PROs for IBD that can be incorporated into trials, to better compare patients' experience with different therapies.

The burden of inflammatory bowel disease: a patient-reported qualitative analysis and development of a conceptual model

BACKGROUND

The aim of this study was to describe the impacts of inflammatory bowel disease (IBD) from the patients' perspective and to inform the development of a conceptual model.

METHODS

Focus groups and one-on-one interviews were undertaken in adult patients with IBD. Transcripts from the focus groups and interviews were analyzed to identify themes and links between themes, assisted by qualitative data software MaxQDA. Themes from the qualitative research were supplemented with those reported in the literature and concepts included in IBD-specific patient-reported outcome measures.

RESULTS

Twenty-seven patients participated. Key physical symptoms included pain, bowel-related symptoms such as frequency, urgency, incontinence, diarrhea, passing blood, and systemic symptoms such as weight loss and fatigue. Participants described continuing and variable symptom experiences. IBD symptoms caused immediate disruption of activities but also had ongoing impacts on daily activities, including dietary restrictions, lifestyle changes, and maintaining close proximity to a toilet. More distal impacts included interference with work, school, parenting, social and leisure activities, relationships, and psychological well-being. The inconvenience of rectal medications, refrigerated biologics, and medication refills emerged as novel burdens not identified in existing patient-reported outcome measures.

CONCLUSIONS

IBD symptoms cause immediate disruption in activities, but patients may continue to experience some symptoms on a chronic basis. The conceptual model presented here may be useful for identifying target concepts for measurement in future studies in IBD.

Health determining concepts important to people with Crohn's disease and their coverage by patient-reported outcomes of health and wellbeing

BACKGROUND AND AIMS

Busy clinical settings often restrict the possibility to focus on concepts that determine health in a positive way, commonly assessed by using patient-reported outcomes (PROs). We aimed to explore which determinants of health (DHs) are important to people with Crohn's disease (CD), to understand possible gender differences and to analyze whether these DHs are covered by PROs used in CD.

METHODS

Two systematic literature reviews were done to identify relevant DHs and clinically relevant PROs. We conducted a qualitative narrative biographical study and mapped the patients' experiences to concepts that determine health in a positive way. Experiences, DHs and the items of the PROs were compared by the WHO International Classification of Functioning, Disability and Health (ICF) as a common framework.

RESULTS

15 people with CD with a median age of 46 years (IQR 34-60) and median disease duration of 15 years (IQR 8-30) participated. Self-efficacy, social support, job satisfaction and occupational balance were mentioned most frequently. While participation appeared to have greater meaning to men, appreciation and resilience seemed to be more important for women. Of 18 PROs the Perceived Stress Questionnaire (PSQ), the Inflammatory Bowel disease - Self-efficacy scale (IBD-SES), the Life Orientation Test - Revised (LOT-R) and the Patient Activation Measure 13 (PAM-13) cover most DHs.

CONCLUSIONS

This is the first study elaborating the coverage of patient's perspective by commonly used PROs in CD. The findings could support health professionals to focus on DHs in people with CD in clinical practice and research.

Restoration of quality of life of patients with inflammatory bowel disease after one year with antiTNFα treatment

BACKGROUND

Inflammatory bowel disease impairs patients' health related quality of life (HRQOL). AntiTNFα agents control disease activity effectively. An ambitious goal of treatment is to achieve the normalization of health. This can be assessed by using a cut-off scoring threshold of the IBDQ-36 questionnaire. It has not been established if antiTNFα treatment is able to restore to normal patients' HRQOL.

AIMS

To determine whether patients with Crohn's disease (CD) and ulcerative colitis (UC) in clinical remission after one year treatment with antiTNFα agents achieve normalization of their HRQOL.

METHODS

Observational and cross-sectional study in patients treated with antiTNFα for one year and in sustained clinical remission. Patients completed the specific questionnaire IBDQ-36. Complete restoration of health was considered achieved when global score of IBDQ-36 was higher than 209 points.

RESULTS

54 patients (43 with CD and 11 with UC) were included. Thirty patients received adalimumab and 24 infliximab. Median global score of the IBDQ-36 was 231, without differences between CD and UC (228 vs 235 respectively, p=ns). Normalization of HRQOL was achieved in all 11 UC patients and in 29 out of 43 CD patients (67%). In our sample population, restoration of health was significantly more frequent in UC than in CD (p<0.05).

CONCLUSIONS

One-year clinical remission induced by antiTNFα treatment restores perception of health to normal in most patients with IBD.

Mucosal healing restores normal health and quality of life in patients with inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD) is a debilitating immune disorder that impairs function and health-related quality of life (HRQOL). A goal of IBD treatment is mucosal healing, but it is not known whether it achieves normalization of the patients' perception of health. This can be assessed by using a cut-off scoring threshold of the Inflammatory Bowel Disease Questonnaire-36 (IBDQ-36).

AIMS

To determine whether patients with Crohn's disease (CD) and ulcerative colitis (UC) in clinical remission and with mucosal healing normalize their HRQOL.

METHODS

This is a multicentric, prospective, observational, cross-sectional study of patients who are in stable clinical remission and having mucosal healing. Patients completed the IBDQ-36, the EuroQol-5D, and the Daily Fatigue Impact Scale fatigue questionnaires. Complete restoration of health was believed to have occurred when the global score in the IBDQ-36 was at least 209 points.

RESULTS

A total of 115 patients (48 with CD, 67 with UC) were included. The median activity index (the Harvey-Bradshaw or the colitis activity index) was 1.0 and the median endoscopic index (Simple Endoscopic Score for Crohn's disease or Mayo) was 0. Eighty percent of the patients (79% in CD and 82% in UC patients, P=NS) normalized their HRQOL. Type of treatment was not related to normalization of HRQOL. The lack of restoration of health was significantly related to fatigue and anxiety/depression.

CONCLUSION

Mucosal healing is associated with a normalization of the perception of health by most IBD patients independently of treatment. However, a significant group of patients do not achieve restoration of HRQOL, which reinforces the necessity of a global care addressed to all patient concerns to achieve patients' complete health restoration.

Disability in inflammatory bowel disease

Disability can include different aspects of patient’s quality of life from physical to psychosocial to employment. Disability in IBD patients contributes to loss of workplace personnel, increased sick leave, and other indirect costs to society. Considerations for more expensive treatment regimens should include their potential to reduce indirect costs to the individual patients and to society in general. The recently developed tool could help establish specific criteria in a set of these diseases that have varied effects and severity.