Taking an occupational history

An inadequate occupational history may result in labelling an illness as not “occupational” when it is, or vice-versa. It may result in missing the diagnosis altogether and in losing an opportunity (or even the last or only opportunity) of making the patient better and improving the fate of other workers. As in other aspects of medical history taking, two important lines of enquiry that must be followed are questions designed to elicit information about the:

• Symptoms of existing underlying pathology;
• Background which may increase the likelihood of such pathology.

In occupational medicine as in other aspects of medicine, the history taking may also fulfil other functions, for example, in attempting to determine the response to a particular problem.

Remember that in occupational (and environmental) medicine it is just as important (perhaps more so) to ask what man has as symptoms as it is to ask what symptoms the man has.

In relation to the symptoms themselves, questioning may elicit:

• The organ system and type of pathological process involved, e.g. wheeze, chest tightness and cough would suggest asthma, red itchy spots on a dry skin would suggest eczema/dermatitis

But, most importantly in taking occupational history it is important to determine exposure:

A job title is not adequate

A full description of what the job entails is a bare minimum. What does an ‘electro-plater’ do, or a ‘ram-block packer’!? The full job description may need to go back several years - mesothelioma for example can occur 40 years after first exposure to asbestos. Indeed in some circumstances it is important to take an occupational history going as far back as the patient’s first job (an environmental exposure history has rarely had to extend even to the pre-school years - as in the case of children who had played on tips containing asbestos or other hazardous substances).

The identity of any chemical exposures or other hazards must be clearly established

Colloquial terms may be used for chemicals, e.g. “trike” (trichloroethylene), “perk” (perchloroethylene), or “monkey dung” (brown asbestos). Confirmation of the identity of a chemical might involve asking the patient to bring in a label or a hazard data sheet. For example, if the history is suggestive of exposure to formaldehyde, then the label of the drum should confirm this.

It is important to try and determine the duration and intensity of exposure

Determining when exposure started, when it finished and how often it was repeated may be tedious but not very difficult. However determining the intensity of exposure by history taking is very difficult. The following are useful guides:

1. How was the task done, e.g. was an adhesive applied with a paint brush while the patient leant over it?
2. Was the dust concentration so bad that one could not see clearly through it, or the noise so loud that communication was difficult?
3. If control of exposure to a chemical appeared poor, what sort of quantities of it were handled?
4. Was there any attempt at segregating harmful tasks, or providing local exhaust ventilation?
5. Special questions are warranted in relation to personal protection. A response that the worker wears a mask is about as informative as a patient saying that he takes small white pills. Many masks offer no protection whatsoever against gases vapours or dust, e.g. surgical masks or old gauze masks, while “nuisance dust” masks of the sort often sold in DIY shops are not much better.
   Different categories of harmful agents tend to have different and specific forms of personal protection. For example, masks designed for respirable dust will not protect from sulphur dioxide or solvent exposure. Thus gloves that may be suited to provide some protection against cement dust might not be of any use at all if exposed to petrol.
6. The control measures, e.g. local exhaust ventilation and personal protective equipment need to be regularly maintained. Ask the worker whether they are and who is responsible for this. In the image example (on the right), a wide range of high quality, well maintained protective measures are in use.

There are a number of similarities between the processing of information in a clinical occupational medical history and the decisions regarding criteria for causal association that one encounters in epidemiology. Indeed many good occupational physicians practise both clinical medicine and epidemiology within the specialty of occupational medicine.

Analogies between determining causality in an epidemiologic context (the Bradford-Hill criteria) in population studies and when dealing with an individual patient in a clinical context.

Note: judgements in relation to the above should be made ‘in the round’. For example, just because a worker complaining of shortness of breath happens to be a smoker does not necessarily mean that his symptoms can be ascribed to smoking.

Summary

In conclusion, while taking an occupational history various avenues need to be explored:

• One may wish to try and confirm suspicions by seeking links between various aspects of the history. For example, if the patient has symptoms of asthma and is exposed to agents which might cause asthma, it will be reasonable to ask when the symptoms are at their worst and when they are at their best. Are they improved after a weekend off work, or better still after a fortnight’s holiday?
• Is there any other evidence of corroboration, such as similar symptoms in other workers?
• Alternative explanations might be explored. Is the patient a smoker? Does he engage in any “do it yourself” activities at home, hobbies or moonlighting? Find out more!
• While a working diagnosis is forming in your mind, you might also be considering ways to help and start asking relevant probing questions. What is the patient’s attitude? And the employer’s attitude? What resources and expertise may be available to provide further information or to assist rehabilitation?

• Influence of work on health
• Hazard and risk