Health Surveillance

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Periodic health surveillance for occupational asthma aims to identify sensitised workers or cases of asthma at an early and reversible stage of the disease. Very few, and no concurrent comparison studies have been reported of the efficacy of health surveillance in occupational asthma. The only study from which valid conclusions can be drawn is of isocyanate workers in Canada, in whom regular health surveillance was linked to a mandatory programme of control of isocyanate exposure at work. . Cases of isocyanate-induced asthma were diagnosed sooner after the onset of symptoms, had better lung function and a better outcome than asthma attributed to other workplace agents not subject to the control programme (Tarlo 2002). It is difficult to dissociate the effects of health surveillance from the effects of other risk management procedures and the authors of the report recognised that the improved outcome in the isocyanate workers might, at least in part, be attributable to the concomitant reduction in isocyanate exposure.

Health Surveillance

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Health surveillance can detect occupational asthma at an earlier stage of disease and outcome is improved in workers who are included in a health surveillance programme.

( Tarlo 2002)

Methods commonly used in surveillance to identify cases of occupational asthma are respiratory questionnaire, spirometry (to measure FEV1 and FVC) and, where appropriate, identification of specific IgE by skin prick test or serology. Very few published reports have evaluated the components of surveillance used in occupational asthma. There is no generally accepted questionnaire for use in surveillance for occupational asthma. Studies of the value of questionnaires to detect asthma suggest that they are insensitive (Gordon 1997, Stenton 1993).

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Screening questionnaires may lead to an underestimate of the prevalence of asthmatic symptoms.

( Gordon 1997, Stenton 1993)

There have been few small studies of case identification of occupational asthma through surveillance of workers at risk. In one study all true cases of occupational asthma were identified by questionnaire. Spirometry identified many false positives due to poor inspiratory effort and no additional cases of asthma (Kraw 1999). In another study spirometry detected one case of occupational asthma in addition to the two cases identified by questionnaire (Bernstein 1993).

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Spirometry detects few cases of occupational asthma that would not otherwise be detected by respiratory questionnaire.

( Bernstein 1993, Kraw 1999)

Skin prick tests and serological tests can detect specific IgE in workers who have become sensitised to high molecular weight allergens and a few low molecular weight chemicals (complex platinum salts, acid anhydrides and some reactive dyes). Tests for specific IgE to isocyanates are insensitive (about 70% false negative rate) but specific (Tee 1998). Since IgE sensitisation is related to exposure, measurement of sensitisation rates in working populations can be used as a measure of the effectiveness of the control of exposure. Higher rates of sensitisation in a workforce reflect poor control and an increased risk of occupational rhinitis and/or occupational asthma in workers.

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Skin prick testing and blood sampling of exposed workers to conduct immunological tests is feasible in the workplace.

( Merget 1988, Redlich 2001)

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Prospective surveillance for the development of specific IgE antibodies can be used as part of a broader risk management programme to reduce the incidence of occupational asthma.

( Flood 1985, Juniper 1977)