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JIRA IHTSDO-796 (artf6364) Occupational disorder modeling Documentation Review

Amendment History

Review Timetable

© International Health Terminology Standards Development Organisation 2012. All rights reserved.
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Table of Contents
1 Glossary
1.1 Domain Terms
2 Introduction
2.1 Purpose
2.2 Audience
2.3 Summary Recommendation
3 Statement of the problem or need
3.1 Summary of problem or need, as reported
3.2 Summary of requested solution
3.3 Statement of problem as understood
3.3.1 Further exploration of the problem
3.4 Analysis of reported problem, including background
3.4.1 Defining 'Occupational disorder'
3.4.2 Background in Epidemiology
3.4.3 Current definition of occupational disorders in SNOMED CT
3.4.4 The SNOMED CT user business case – Occupational health interventions, occupational disease reporting and surveillance
3.4.5 Extent of problem in SNOMED CT – quantification
3.4.6 Summary of classification issues
3.4.7 Causality/causation in disorders and findings in SNOMED CT
4 Risks / Benefits
4.1 Risks of not addressing the problem
4.2 Risks of addressing the problem
5 Requirements: criteria for success and completion
5.1 Criteria for success/completion
5.2 Strategic and/or specific operational use cases
6 Solution Development
6.1 Initial Design
6.1.1 Solution 1: Full definition of occupational disorders using Due to (attribute)
6.1.2 Solution 2: Don't attempt wholesale full definition
6.2 Design Risks
7 Recommendation
7.1 Detailed design final specification
7.2 Content for review as part of 7.1
8 Quality program criteria
8.1 Quality metrics
8.1.1 Quality metric 1
8.1.2 Quality metric 2
8.2 Use case scenarios
9 Project Resource Estimates
9.1 Scope of elaboration phase
9.2 Projection of overall project size and resource requirements
9.2.1 Expected project resource requirement
9.2.2 Expected project impact and benefit
9.3 Scope of construction phase
9.4 Projection of remaining overall project resource requirements
9.4.1 Expected project resource requirement category
9.4.2 Expected project impact and benefit
9.4.3 Indicative resource estimates for construction, transition and maintenance:
10 References

Glossary

Domain Terms

Introduction

Purpose

The purpose of this project is to consider improving the modeling of the concept 115966001 Occupational disorder (disorder) so as to fully define it and hence to appropriately subsume all thus defined occupational disorder content.

SNOMED CT projects transition from Inception Phase  Elaboration Phase  Construction Phase  Transition Phase. This document combines the documentation of the Inception and Elaboration Phases.
The Inception Phase focuses on understanding the problem and its scope, identifying stakeholders and their requirements, and identifying risks.
The purpose of the Elaboration Phase is to develop, document and test one (or more) possible technical solutions, and to reach a recommendation and provide a detailed specification of a preferred solution to be taken forward to the construction phase.

Audience

The audience for this document includes all standards terminology leaders, implementers and users but is especially targeted at those stakeholders from the epidemiology and occupational health domains and others needing to record and report on disorders with an occupational cause so that public health policy and legislation can benefit (and ultimately the general population). The technical nature of the issue and of the possible solutions makes securing public health insight difficult and of questionable value at the inception phase. As enhancement of definition is beneficial or at least neutral then, if this can be done in a way that does not adversely affect other content, there is no need for wider consultation at this point.

Summary Recommendation

The recommended solution is to not attempt wholesale full definition of disorders for their work-relatedness but instead to use a situation concept to record occupational history: 705133000 | History of exposure to occupational risk factor (situation) such that this coding complements the primary diagnosis record. The solution is set out in detail in Sections 6 and 7 but involves one new Event concept and some modeling of content not previously modeled (but in line with current policy not an extension of it).

Statement of the problem or need

Summary of problem or need, as reported

Artifact artf6364 in the IHTSDO Tracker list initiated by Kent Spackman in 2010 describes the problem thus:
Occupational disorder does not have a clear model, and might be something that should be post-coordinated.
E.g. "occupational asthma" is not currently under "asthma".
And occupational disorder is primitive. It needs to become fully defined.
The item does not have any 'Associations' or 'Dependencies' identified in the Tracker in respect of other projects.

Summary of requested solution

As above, the proposal is that a model is developed to allow for occupational disorders to be fully defined. No detail is available on possible models that meet this requirement.

Statement of problem as understood

The statement in the Tracker artifact "'occupational asthma' is not currently under 'asthma'" is no longer true; this anomaly has been corrected with the concept now a subtype of 424199006 | Substance induced asthma (disorder). However, there has been no advance in modeling the concepts through other defining attributes.
The problem can be summarised as a concern that a) not all disorders defined as subtypes of 115966001 | Occupational disorder (disorder) are sufficiently classified by etiology and pathology and that b) not all occupational disorders in SNOMED CT can be found by the list of stated subtypes of 115966001 | Occupational disorder (disorder).

Further exploration of the problem

Whilst all disorder concepts containing the word 'occupation(al)' can be reliably classified, some disorders with an occupational component may not be worded as 'occupational'. Further, some concepts have 'occupation(al)' references in synonymous descriptions but not in their FSN and are not found under Occupational disorder (disorder).
e.g. 15488007 | Melanodermatitis toxica lichenoides (disorder) has a synonymous description:
'Occupational melanosis' but is not defined in SNOMED CT as an occupational disorder.
There is no explicit reference in the Tracker item on why this exercise is worthwhile except as an appropriate exercise in precise classification; nevertheless it is possible to elaborate a strong use case for this piece of work to allow secondary Public Health data collection and analysis. The value to the patient record and treatment course is less obvious but is explored in section 3.4.4 below.
The problem of reliable classification can be remedied by a systematic review of content for occupational causation and by work to appropriately define content by supertype. However, because this 'single point in time' approach lacks continuity there is a risk of inadequate classification of new content and slow drift away from reliability. Therefore, to ensure a sustainable model, a means of modeling content through other defining attributes is suggested in the tracker item.

Analysis of reported problem, including background

Defining 'Occupational disorder'

Bernardino Ramazzini (1633 – 1714), often called the 'father of Occupational Medicine', proposed that physicians should extend the list of questions that Hippocrates recommended they ask their patients by adding: "What is your occupation?"
The World Health Organization describes an occupational disease as "any disease contracted primarily as a result of an exposure to risk factors arising from work activity". "Work-related diseases have multiple causes, where factors in the work environment may play a role, together with other risk factors, in the development of such diseases."
An "occupational risk factor" is defined by Karjalainen (see below) as "a chemical, physical, biological or other agent that may cause harm to an exposed person in the workplace and is potentially modifiable".
"People at work face a variety of hazards owing to chemicals, biological agents, physical factors, adverse ergonomic conditions, allergens, a complex network of safety risks, and many and varied psychosocial factors. In addition to injuries, more than 100 occupational diseases have been classified according to the tenth revision of the International Classification of Diseases and Related Health Problems (ICD-10). Broadly, these include respiratory, musculoskeletal, cardiovascular, reproductive, neurotoxic, skin and psychological disorders, hearing loss and cancers".
Karjalainen, A: Comparative Quantification of Health Risks Ch21 p1653 World Health Organization http://www.who.int/healthinfo/global_burden_disease/cra/en/
However, as Karjalainen states: "The absence of unified diagnostic criteria, coding systems and classifications reduces the compatibility and comparability of national statistics on occupational diseases."

Background in Epidemiology

In 1900, the three top causes of death in the U.S. were pneumonia, tuberculosis, and gastroenteritis. In 1990, the top causes of death in the U.S. were heart disease, cancer, stroke, accidents and chronic obstructive lung disease and remain so today. This shift from acute infectious cause of death to chronic disease has led to a more contemporary model of disease causation being applied to epidemiology including multiple risk factors, long latency periods, and differences in individual responses to disease causing agents.

Current definition of occupational disorders in SNOMED CT

115966001 | Occupational disorder (disorder) is defined as an environment related disease and is Primitive:

The SNOMED CT user business case – Occupational health interventions, occupational disease reporting and surveillance

The importance of reporting and surveillance of occupationally related disease is well documented. It is beyond the scope of this document to describe this in any detail. However, it is worth noting that occupational repiratory disease surveillance is particularly well organised and established around the world.
"Classifications of occupational diseases have been developed mainly for two purposes: (1) notification for labor safety and health surveillance and (2) compensation." Karjaleinen
"An occupational disease is not characterised merely by the disease itself, but by a combination of a disease and an exposure, as well as an association between these two." ibid
This is a key point. It means that SNOMED representations of both disease and exposure need to be considered.
In looking at SNOMED issues in this matter we may be straying into classifications territory. ICD-10 relies largely on primary diagnoses in notifications where the notification itself gives the occupational context. However most of the content found in SNOMED describing 'occupational disorder' comes from ICD. What is defined in ICD is not automatically what should be defined in SNOMED and the case needs making. In general, there may be no histopathological features to distinguish an occupational case of a disorder from a non-occupational one. Many specified ICD derived lung diseases under 'Extrinsic allergic alveolitis/Hypersensitivity pneumonitis' appear to be only different words for the same thing with a risk factor exposure element added on. Whether it should be left to ICD or to the notification context it might be argued that this can then be left out of scope of SNOMED CT. The requirements for secondary data collections are distinct and separate from those expected of clinical diagnosis. However, to argue the contrary: it may well be germane to the course of care to identify the causal exposure along with the disorder so that the exposure can be removed (if it is still present), limited or mitigated in some way. This does not prevent a cross-map to a less granular ICD-10 primary diagnosis code for notification purposes. It may also be important from an individual perspective to gain a definitive diagnosis that clearly associates the disorder with an occupational exposure for reasons of legal action, compensation or retirement, pensions, care costs etc. even where the course of treatment is the same whether occupational or non-occupational in origin. Where the individual is still working in the same environment then occupational health interventions could be identified and coded to remedy or mitigate the risk and even in cases where the individual has moved on or retired there still remain sound reasons for recording the origin of the condition to their or others' advantage. It may simply be that, despite it not affecting the clinical treatment course, "ars longa…" makes going the extra distance to record the causative or at least associated environmental factor worthwhile and the diligent clinical historian may be thanked by posterity.

Extent of problem in SNOMED CT – quantification

The Tracker item presents the possibility of diseases with an occupational component not being classified as such and conversely the risk of some subtypes of 115966001 Occupational disorder (disorder) not being additionally classified by their pathology/aetiology in some way.

Content classified under 115966001 Occupational disorder (disorder)

The (July 2015 Edition) list of 100 subtypes of 115966001 Occupational disorder (disorder) :

(NB The subtypes are further nested but are presented here as a flat alphabetical list for readability.)
A check on this content shows that most of these concepts have at least one supertype outside the hierarchy grouper. Only two concepts are subsumed only by the hierarchy grouper. These are:
95877004 | Gulf war syndrome (disorder)
On initial consideration, this might attract an additional parent for example 281867008 | Multisystem disorder (disorder) alongside Chronic Fatigue Syndrome.
40897007 | Occupational deafness (disorder)
This has a child concept 84063009 | Traumatic deafness, occupational (disorder) which has additional parents and is Fully Defined. However, this child concept does not attract as a parent: 89496002 | Traumatic deafness (disorder) which subsumes 72964008 | Traumatic deafness, non-occupational (disorder). 15188001 | Hearing loss (disorder) might well provide an additional defining supertype for 40897007 | Occupational deafness (disorder).
115966001 | Occupational disorder (disorder) has 13 stated subtypes, of which six are branch nodes. Only 86157004 | Occupational lung disease (disorder) has any significant number of subtypes, the others having only one to four leaf node subtypes each. 402587003 | Occupational dermatitis (disorder) has no subtypes and 371128008 | Occupational injury (disorder) has only three leaf node subtypes.
There is a small set of concepts of a format slightly out of step with disorders:
55487001 | Employer in work-related accident (disorder)
42270002 | Visitor in work related accident (disorder)
81485008 | Worker in work-related accident (disorder)
78265006 | Co-worker in work-related accident (disorder)
These are subtypes of 65339005 | Disorder due to work-related activity accident (disorder). They do not affect the main subject under review and because slightly anomalous will be left to one side as potential exceptions or as requiring further review as to appropriate classification.

Review of SNOMED content associated with occupation but not classified under 115966001 Occupational disorder (disorder)

By way of an initial check on the scale of the presented problem a set of searches was run on the tokens 'occupation(al)', 'industr' and 'work(er)'. These searches returned the following content not subsumed by 115966001 Occupational disorder (disorder):
<42812006 | Specific bursitis often of occupational origin (disorder)
77678000 | Beat elbow (disorder)
29381009 | Beat hand (disorder)
37294008 | Beat knee (disorder)
63517006 | Miner's elbow (disorder)
52334005 | Miner's knee (disorder)
10586006 | Occupation-related stress disorder (disorder)
22343003 | Pneumonitis due to fumes AND/OR vapors (disorder) (synonymous description: Chemical workers' lung)
242386005 | Accidental exposure to carbon monoxide in industry (event)
446175003 | Acute posttraumatic stress disorder following military combat (disorder)
699241002 | Chronic post-traumatic stress disorder following military combat (disorder)
242386005 | Accidental exposure to carbon monoxide in industry (event)
Subtypes of 37471005 | Extrinsic allergic alveolitis (disorder)
e.g 11944003 | Feather-pickers' disease (disorder)
Many injury concepts under 419945001 | Traumatic injury due to event (disorder) refer to specific occupations being injured such as crew, stevedore etc which would implicitly allow them to be classified as occupational.
Found cases where disorder may be occupationally related but not exclusively so:
21180000 | Industrial environment related disease (disorder)
77377001 | Leptospirosis (disorder) (synonymous descriptions: Rice-field worker's disease and Cane cutter's fever)
217935007 | Accident caused by agricultural machine (event)
109378008 | Mesothelioma (malignant, clinical disorder) (disorder)
45231001 | Infrapatellar bursitis (disorder) (synonym Clergyman's knee)
(The historic 'Housemaid's knee' is no longer current in SNOMED CT)
In practice, many of the disorders referring to a rich multiplicity of occupations may terminate in very similar disease presentations, for example lung disorders or arthritides/bursitides.
Occupational disorders and occupational injuries
371128008 | Occupational injury (disorder) only has three subtypes. Although any number of injuries can be occupational in origin, hardly any are designated as occupational. In looking for a solution to the presented problem it is unlikely that there is a need to precoordinate content in this area but a postcoordination option might be considered. For example an amateur soccer player could not sustain an anterior cruciate ligament occupational injury but such an injury sustained by a professional player might be postcoordinated as occupational.
Occupational injuries are defined as occupational disorders but some occupational disorders are also caused by occupational injuries. For example in a case of hepatitis B through needle stick injury in a health worker the disorder is 'DUE TO' the inoculation from the needle stick injury. Although vectors of disease are not usually modelled, the basic 'hepatitis B with causative agent hepatitis B virus' does not allow for capture of the vital information that accidental occupational inoculation was involved. However, the model allows for multiple values and might therefore theoretically also take the putative Event value 'Occupational exposure to blood-borne pathogen' or merely 'Exposure to occupational risk factor'. The AFTER attribute could also be used here although this seems to be used more commonly for post-procedural findings. Here one should note that hepatitis B virus infection is indifferent to whether it's introduction was occupational or otherwise.
An occupational injury is, on reflection, somewhat ambiguous; there is a difference between an accidental injury sustained at work and one caused by the nature of the work activity itself although there is a large gray area here. The distinction can be hard to draw; getting a hand caught in machinery is clear, a repetitive task with a joint-stressing impact means that the instance isn't capturable in the same way and the association between activity and harm harder to confirm beyond doubt. Some occupations are inherently more hazardous than others. Occupational disorder as a definition covers all of this area from injuries that were incidentally in a workplace to single occupational minor accidental injuries with full recovery to catastrophic life-changing disorders caused by single or constant exposure. The task of definition comes up against arguments of SNOMED scope and of utility. The absence of defined subypes of 371128008 | Occupational injury (disorder) may be for good reason. The case remains unclear about what added value there is in stating some disorder is 'occupational' where the occupation is to be stated as the cause of the disorder but the causation may not be assertable or the disorder is caused by an event with commonalities across settings (e.g. struck by object or vehicle in workplace).
Accidental injury and exposure
There is a further difficulty in classifying accidental injury or exposure to occupational risk factor/agent in that there may be some undetermined element of employer negligence or even of wilfull disregard for employee safety. It is of no small import then to code work injuries but it is still hard to do.

Summary of classification issues

As only two codes in the hierarchy under examination do not have other supertypes then this is a small scale issue. However, subtypes with more than one supertype are inconsistent in that some are fully defined because of their additional modeling but some are not. For example 201220003 | Occupational acne (disorder) is primitive but 111343004 | Occupational erosion of teeth (disorder) is fully defined.
This inconsistency is unpredictable and will continue unless additional modeling is introduced. On the other hand 'acne' in the above case lacks definition beyond it being occupational and might be argued to be rightly primitive and childless – one cannot say definitively that e.g. 83684005 | Chlorine acne (disorder) is occupational. The number of concepts that are explicitly occupation-related but not classified as such is again low. What is more open to examination is the volume of disorder content where the textual representation carries no explicit indication of occupational exposure or otherwise.

Causality/causation in disorders and findings in SNOMED CT

(note: the words causation and causality are used interchangeably here for simplicity)
The SNOMED CT Editorial Guide (in the nested section 6.1.3.17.1 Disorder Combinations) makes a start on defining the causation model for disorders; this is in the process of development, extension and implementation, It provides a useful "truth table" However it describes disorder1 + disorder2 combinations only and not disorder+event or finding+disorder.
Causation is philosophically vexed territory for SNOMED to be getting entangled in and usefulness must remain one of the terminology's tenets; the pursuit of causative purity is not the sole objective.
Necessary and sufficient conditions between states can be asserted with reasonable certainty but as John Mackie proposed:
"a cause of some particular event is 'an insufficient but non-redundant part of a condition which is itself unnecessary but sufficient for the result' (Mackie 1974: 62). Mackie called a condition of this kind an INUS condition, after the initial letters of the main words used in the definition. Thus, when experts declare a short-circuit to be the cause of fire, they "are saying in effect that the short-circuit is a condition of this sort, that it occurred, that the other conditions which, conjoined with it, form a sufficient condition were also present, and that no other sufficient condition of the house's catching fire was present on this occasion" (Mackie [1965] 1993: 34). Thus, Mackie's view may be expressed roughly in the following definition of 'cause': an event A is the cause of an event B if A is a non-redundant part of a complex condition C, which, though sufficient, is not necessary for the effect (B)."
Causality and Causation: The Inadequacy of the Received View, Hulswit M, University of Nijmegen (undated). http://see.library.utoronto.ca/SEED/Vol4-2/Hulswit.htm
This is complex. This could be used to argue that, even if not the sole cause, it is sufficient when in combination to be a valid assertion - or it could be used to argue the opposite; that causation is too complex to capture in current modeling. Is occupational asthma solely occupational? Is the patient a smoker or passive smoker? Was there a pre-existing pulmonary problem? How long ago was the exposure? Etc. It may be better to avoid such territory for now and choose to say that short-circuit/dust exposure and house fire/lung disorder are both things established as true about the patient but nothing more.
Causation is also made harder where, because such things are hard wired into human thinking and language; metonymically, clinical terms for complicated sequelae are commonly constructed to only imply these states by reference to the simpler antecedent pathologies that caused them. For example 21794005 | Radial styloid tenosynovitis (disorder) has a synonym of 'de Quervain's disease' when actually the second is a consequence of the first.
There is a considerable amount of precoordinated disorder content where one disorder is described as being due to another disorder. This is in keeping with the concept model group of 'Associated with with', 'Due to', 'Following/After'. For example:

The SNOMED concept model is currently being developed to define unambiguously content that was previously classified using 'Associated with' as either 'Due to' or 'Co-occurrent with' (or both). In content addition, a choice is available to assert a clear 'DUE TO' relationship or to leave this unstated as 'following' or 'co-occurrent with'. In the case of occupational disease the exposure may be temporally co-occurrent or in the distant past. The exposure can be in the nature of a single instance, of repeated exposures or of continuous exposure. Conditions may stop on removal of the provoking factor or persist long after the exposure has ended. The assertions to be made must be clearly determined from requesters and clear editorial statements made to allow for clear and appropriate pre- and postcooordinated content, without unwarranted assertions of causality. The degree of work-relatedness of a condition may not be easy or even possible to establish or quantify. Empirically, removing the stimulus may abate the condition but it is still another step to say that therefore the condition is due to the stimulus (exposure).
42752001 Due to (attribute) would often seem to definitively cover causation but in the example of Anthrax the cause is Bacillus anthracis and transmission is cutaneous or by inhalation or ingestion but ultimately, usually the result of occupational exposure to infected animals or their products. However the exposure component is not available in SNOMED as a definition.
The concept model for 42752001 Due to (attribute) allows for values from Finding and from Event hierarchies although in practice the Event hierarchy seems under-represented. There is no use of the large hierarchy <<418715001 | Exposure to potentially harmful entity (event); but, notably in this context, this hierarchy contains few concepts identifying exposure to risk factors for occupational disease explicitly except for some subtypes of 102420004 | Exposure to pollution (event) e.g. 102442003 | Exposure to toxic agricultural agents, occupational (event). Nor is there a grouper concept that could be used to head such occupational risk factor exposures e.g. 'Exposure to occupational risk factor (event)'.
255234002 | After (attribute) is also still described in the Editorial Guide as useable in this context. "This attribute is used to model concepts in which a clinical finding occurs after another clinical finding or (more commonly in SNOMED) procedure. Neither asserting nor excluding a causal relationship, it instead emphasises a sequence of events." It can take values from Clinical Finding | 404684003 and Procedure | 71388002. Note that it does not allow values from the Events hierarchy. However, as the 'Associated with' model is under review it may be opportune to either specifically include events or exclude them in editorial guidance.
The use of 'exposure' events in modeling disorders may well be limited by the set of attributes available. It is out of the scope of this limited investigation to describe causality in any detail but whatever the case for the embedding of a fuller causation model in SNOMED, the development should at least perhaps account for temporal disjunctions where disorder and causative factor are not co-occurrent (if co-occurrence is defined as being synonymous with contemporaneity or closeness in time).
Situations
705133000 | History of exposure to occupational risk factor (situation)
161635002 | History of asbestos exposure (situation)
442029006 | History of exposure to lead (situation)
These contextualised concepts seem at first glance outliers to a systematic approach to classifying such exposures. While allowing for a clinical statement of history, they do not directly allow for an assertion of disease causation or association except through values of '246090004 | Associated finding (attribute)'. 'Associated finding' includes in its value range '272379006 Event'.
705133000 | History of exposure to occupational risk factor (situation) does not have a specific value asserted for '246090004 | Associated finding' of the form: 'Exposure to occupational risk factor' but such a modeling solution is possible and permissible. These present an interesting dimension to clinical recording and this contextual content is considered at greater length in section 6 below.
It is worth noting the following perhaps anomalous 'situation' concepts:
444237009 | Risk of exposure to Leptospira (situation)
443999008 | Risk of exposure to communicable disease (situation)
Environments
As part of a comprehensive review it is also appropriate to make reference to 276339004 | Environment (environment). Along with the large, combinatorial, classification derived hierarchy 216312009 | Place of occurrence of accident or poisoning (environment) there are the semantically relevant:
285141008 | Work environment (environment)
224815004 | Industrial environment (environment)
272505000 | Industrial site (environment)
etc
However none of these environments preclude a non-occupational reference as an individual might be on a site without having an occupation there but, even if they were valid or if appropriate new content were added, the concept model does not have an approved means of incorporating the still, in general terms, underdefined <276339004 | Environment (environment) as a value set in formal definitions for clinical findings. There may be a case for review in a separate project to explore such a development case but it would seem on the face of it that the term 'x environment' is not sufficiently freighted with context to be useful in definition here.
Subsidiary and interrelated problems
See section 3.4.6 above.

Risks / Benefits

Risks of not addressing the problem

If occupational disease content cannot be fully defined it cannot be reliably returned from searches for diagnosed occupational causation. Where this is required for insurers or care provider organisations to report to State or National surveillance bodies there is a risk of undermining the quality of such returns thus making the work of such organisations in directing policy and resources more difficult. The ultimate risks are to individuals who may be exposed to occupational risks for longer than necessary because the statistical reports on adverse consequences of various workplace exposures have been less well informed. This in turn has a significant cost at national level around the world in managing the disease consequences of exposure to workplace risks.
While the clinical course of treatment may be unaffected by occupation, the removal of the exposure is likely to be important and identifying that exposure in the record will support its being addressed, it's absence may mean exposure continues, affecting treatment response and long term outcome.

Risks of addressing the problem

As improvements to classification of exposure and disorder would support more accurate use the risks seem minimal but full definition of the domain in SNOMED seems problematic and hard to sustain. There may be a risk of content being classified as exclusively occupational where other causes are possible although clear guidance on classification for editors might mitigate this risk.
As the types of harmful occupational exposures are myriad there is a risk of combinatorial proliferation of precoordinated content. This risk could be managed by ensuring an approach that precoordinates explicitly occupationally related disorder content only at a limited high level with occupational exposure as a general term rather than with detailed enumerations of subtypes of exposure. SNOMED CT users could use a single occupational risk exposure attribute/value in postcooordinating expressions where needed.

Requirements: criteria for success and completion

Criteria for success/completion

The main criterion for success is the development of the SNOMED concept model so as to allow occupational disorders to be fully defined. In addition, IHTSDO should be able to state confidently that SNOMED CT defines occupational diseases comprehensively so as to allow for secondary use of data for statistical and surveillance purposes.
However, there is an assumption here that full definition is to be applied to all content where an occupational factor is possible. In fact many disorders even where commonly work-related may also be found in people not engaged in their work. For example mesothelioma has had some incidence in women washing the asbestos-contaminated work clothes of their spouses. Feather-pickers' disease (disorder) may well be occupational but might not be exclusively so. A daily domestic exposure could account for the same disease and the term does not clearly state that the disease is occupational. Occupational disorder is not a necessary and sufficient condition to assert the IS-A relationship from Feather-pickers' disease despite the implicit sense of work-relatedness.
It may be possible to scrutinise this assumption further and question the value of "Occupational disorder" as a SNOMED CT concept. It is certainly valuable in classification systems, but within the terminology, putative subtypes are necessarily always occupational disorders. It is arguable then that the concept while mapped from classifications as a primitive concept does not warrant classification as a supertype unless the disorder is exclusively occupational. It follows that while it may be possible to validate existing subsumption on this criterion, there would always be content that remains outside this definition, hence the reviewed content being sporadic is not to be assumed to be wrong even if it is at first glance problematic for data collection. It is therefore appropriate to consider a range of possible solution options that might serve to capture occupational risk exposure effectively; solutions which might unavoidably require more than one code to encapsulate.

Strategic and/or specific operational use cases

Outline fit with IHTSDO strategic goals
The first of the five strategic directions is 'Make it easier to use SNOMED CT for priority use cases'; these are identified as facilitating the accurate collection and sharing of clinical, public health, and related health information through improving the semantic representation and interoperability of health records (including personal health records and those created by health professionals); (2) contributing to improved delivery of care by the clinical and social care professions through supporting efficient, effective, and safe decision support; and (3) enabling "health system" or "secondary" uses of data held in individuals' health records.
Any changes should support clinicians in setting out a plan of care that specifically addresses the occupational component in an individual's disorder and allows health system or secondary use of data by the improved and explicit capture of occupational causation or contribution to disease and would inform public health policy and resource allocation.
Although no specific 2015 work items can be cited in support, the overall  "fit for purpose" case and the strategic direction of "improving the semantic representation and interoperability of health records" are strong justifications for addressing this issue with a modest resource input.

Solution Development

Initial Design

Two options (besides a notional do nothing option) are presented, the first allowing full definition of Occupational disorder (disorder), the second leaving occupational disorders as they are currently defined or undefined (although there is an argument for it not subsuming anything as it fails the necessity and sufficiency test) and using 'History of exposure to occupational risk factor (situation)' to define the exposure.

Solution 1: Full definition of occupational disorders using Due to (attribute)

Due to a Clinical Finding: Exposure to occupational risk factor
or
Due to an Event: Exposure to occupational risk factor
In this solution space, the problem has two associated issues; 1. supporting full definition and 2. aligning new and existing content with the new definition model.
In order to achieve a full definition of occupational disorders a means of doing so through the concept model would be needed. The addition of a causal relationship attribute ('Due To') to 115966001 | Occupational disorder (disorder) would allow a definition to be asserted that would allow for concepts to be conceptually distinct and fully defined. No change to the concept model is needed for this however it would be necessary to provide guidance to editors in seeking clarity on the occupational context of relevant new disorders.


should be updated to:

This entails the addition of a new concept:
'Exposure to occupational (disorder?) risk factor (event)'
as a subtype of 418715001 | Exposure to potentially harmful entity (event).
In the example below of 'Occupational dermatitis', this would in turn allow:

to be defined as:

This approach might be given further strength if 8504008 | Environment related disease (disorder) were in turn modelled with 418715001 | Exposure to potentially harmful entity (event).

6.1.1.2 Indicative testing

Early testing of the proposed solution shows that content under 115966001 | Occupational disorder (disorder) thereby becomes fully defined on classification (see below).



6.1.1.3 Alignment and definition of content
A systematic review would be needed, to locate and reclassify disease concepts that have an occupational cause as subtypes of the Occupational disorder grouper. This is likely to reveal 50-100 concepts that have an occupational dimension.

1. 1. 1. 1. End user Impact

Specified content would be reliably defined. However, there remains the rest of the disorder hierarchy which does not have any scope for definition by occupational cause. In these cases it may be possible in some systems to use 115966001 | Occupational disorder (disorder) along with the primary clinical diagnosis but this is unreliable. A true post-coordinated approach to defining occupational cause is not presented here as it is part of a wider issue of asserting association and causation. There would appear to be some value in offering such functionality in general but it is not explored here.

Iteration plan

Iteration of the basic proposal could be enacted through modest quantity of work in editing and reclassifying first through a test and then through committted changes.
Some time would be needed to review content open to further modeling. Some additional guidance to editors would need to be drafted subject to identified need.

Solution 2: Don't attempt wholesale full definition

Instead, undertake to consolidate any stray definitively occupational content under 115966001 | Occupational disorder (disorder) and, chiefly, use a situation concept to record occupational history in a separate data field:
705133000 | History of exposure to occupational risk factor (situation)
This would ensure the substance, energy, force etc modeled in the associated finding could be used to mine the patient record data for reporting and surveillance etc.
Section 3.4.4. explored the relationship between SNOMED and ICD-10 in this matter. Some advantage to covering both disorder and exposure to risk of disorder was found to be advantageous. This does not mean that the two should be combined; indeed it may be desirable to keep them separate for analysis and interoperability purposes but to describe how editors and end users might capture work-relatedness without combined concepts.
In common with the rest of <<161632004 | History of risk factor (situation), 705133000 | History of exposure to occupational risk factor (situation) is not currently defined by 246090004 | Associated finding. It should be so defined; temporal context dependent findings and procedures should have a valid temporally neutral finding or procedure as their referrent. It should be noted that 'History of risk factor (situation)' is thus modeled, not with a finding value but with 418715001 | Exposure to potentially harmful entity (event).
Equally 442029006 | History of exposure to lead (situation) should have an Associated finding of Exposure to lead (finding or event). The same applies to 161635002 | History of asbestos exposure (situation), 161636001 | History of isocyanate exposure (situation) etc.
However, the solution does not propose the creation of subsumption of such as 161635002 | History of asbestos exposure (situation) under 705133000 | History of exposure to occupational risk factor (situation) where the work-relatedness is not clear. There is a case to be made for adding subtypes such as 'History of occupational asbestos exposure' should demand for these arise but it is outside the scope of the paper beyond providing the 'scaffolding' for such content development. However, what is germane here is that while the scope to model this context content with <<418715001 | Exposure to potentially harmful entity (event) and this hierarchy seems potentially a rich mine for definition the events hierarchy is primitive – it lacks the scope for modelling the substance, energy or force etc. So while events are initially attractive, a realistic solution should involve modeling 705133000 | History of exposure to occupational risk factor (situation) either with:

• events content that is modeled usefully with the agent to which exposed

or

• findings content that already permits modeling of the agent

However, it is worth noting that significant volumes of findings content has been moved to the events hierarchy in the past and therefore recreating these in Clinical findings would be editorially unwelcome. The alternative, which follows the existing model to where it leaves off, would be to use 418715001 | Exposure to potentially harmful entity (event). The difficulty here is that some of the 418715001 | Exposure to potentially harmful entity (event) sub-hierarchy has some rudimentary modeling but much does not. Notably, <<444071008 | Exposure to organism (event) is modeled reliably, for example:
170475009 | Exposure to Bacillus anthracis (event): 47429007 | Associated with: 21927003 | Bacillus anthracis
However:
699373005 | Exposure to asbestos (event)
218190002 | Exposure to radiation (event)
6300007 | Exposed to noise (event)
45477008 | Exposed to vibration (event)
etc are not modeled.
Egregiously, 95871003 | Exposure to mercury (event) is modeled with 246075003 | Causative agent: 45262002 | Mercury where mercury apparently caused the exposure.
The author notes in passing that 161638000 | Hepatitis B Occupational risk (situation) is a misplaced finding that should really be the 'associated finding' of 'History of hepatitis B occupational risk').

Indicative testing

Because there is little change beyond enriching and better defining the content within the existing model there is little to test.

Alignment and definition of content provide examples of content

Figure1
705133000 History of exposure to occupational risk factor (situation) would be additionally modeled:

Figure 2
Better with a new concept:




Figure 3
Worked example: 161635002 | History of asbestos exposure (situation) modeled

End user impact

Field testing might involve exploring whether a 'History of…(situation)' concept is viable in combination with the primary diagnosis code to adequately capture work related disorders.
Clinicians could then record:

1. History finding: 161635002 | History of asbestos exposure (situation)
2. Primary diagnosis: 22607003 Asbestosis (disorder)

Any new content would be limited to the Events hierarchy to expand the range of values for Associated finding modelled 'History of…(situation)' concepts. The case for expanding any subtypes of occupational exposure (event) (for example: 'Occupational exposure to blood-borne pathogen') would need to be done as a separate exercise.
161635002 | History of asbestos exposure (situation) would be modeled with Associated finding: 699373005 | Exposure to asbestos (event) and in a fully postcoordinated world it would be possible to further refine this to 22222222222 Occupational exposure to asbestos (event) – both modeled with 16369005 Asbestos (substance). Even if this remains too sophisticated in use, clinicians could safely record directly with either 161635002 | History of asbestos exposure (situation) unrefined, 699373005 | Exposure to asbestos (event) or 22222222222 Occupational exposure to asbestos (event). The use case would seem to be covered without creating redundant occupational disorder codes to meet a secondary use case.

Design Risks

See section 4

Recommendation

The recommended solution at this stage of elaboration is:
Solution 2: To not attempt wholesale full definition of disorders but instead to use a situation concept to record occupational history: 705133000 | History of exposure to occupational risk factor (situation) such that this coding complements the primary diagnosis record rather than adds to it.

Detailed design final specification

Modeling for Associated finding and the 'knock-on' modeling of relevant event content forms the bulk of the work and is low volume and apparently low risk as it follows existing modeling policy and merely implements this where there is a gap.
In addition there is a certain amount of quality improvement work where content has been underdefined or is wrongly parented or modeled.

Content for review as part of 7.1

(where anomalous content or modelling was found in passing)

Quality program criteria

Quality metrics

Quality metric 1

Quality metric 2

Use case scenarios

Testing should take place as per section 7.1.1.2 above. If the test case is satisfactory work to commit and QA the changes can take place.

Project Resource Estimates

The project is small-scale and as it requires only a small amount of time can be acted upon at short notice and published in the next release. Costs are minimal and can be subsumed in general editing activity budget and through (in-program) Consultant Terminologist time.

Scope of elaboration phase

This would confirm the recommended approach and identify the content change and content for additional classification

Projection of overall project size and resource requirements

Expected project resource requirement

The project resource requirement is classed as SMALL – less than 1 person year

Expected project impact and benefit

The project impact is MEDIUM – significant improvement to a minority but high profile use case

Scope of construction phase

Limited to single concept addition and review of existing 'hidden' occupation related disorder /finding content

Projection of remaining overall project resource requirements

Expected project resource requirement category

This is a fast track project and does not require project management.

Expected project impact and benefit

Covered in detail in the body of the Inception sections above.

Indicative resource estimates for construction, transition and maintenance:

Construction and transition phase: 1 new concept to be authored
Maintenance phase: No further content additions. Impact of improvement will arise through defining classification of new content going forwards.

References

International statistical classification of diseases and related health problems (ICD-10) in occupational health, A. Karjalainen, Finnish Institute of Occupational Health
WHO/SDE/OEH/99.1, 1999 World Health Organization http://www.who.int/occupational_health/publications/en/oehicd10.pdf?ua=1
Causation in Occupational Disease: Balancing Epidemiology, Law and Manufacturer Conduct, Richard M. Lynch & Mary S. Henifin, Risk: Health, Safety & Environment 259 [Summer 1998]
http://ipmall.info/risk/vol9/summer/lynch.pdf
Models of Causation: Health Determinants, Core Body of Knowledge for the Generalist OHS Professional, Wendy Macdonald, Safety Institute of Australia, 2012.
http://www.ohsbok.org.au/wp-content/uploads/2013/12/33-Models-of-causation-Health-determinants.pdf?ce18fc
Causality and Causation: The Inadequacy of the Received View, Hulswit M, University of Nijmegen (undated). http://see.library.utoronto.ca/SEED/Vol4-2/Hulswit.htm

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