Summary

Individuals with asthma have chronic inflammation in the bronchi (air passages). As a consequence the bronchial walls swell causing the bronchi to narrow, which can lead to breathlessness. Muscles around the air passages also become irritable so that they contract, causing sudden worsening of symptoms in response to various stimuli, including exposures encountered at work.

• The 2006/07 Self-reported Work-related Illness survey estimated that there were 142 000 people with "breathing or lung problems" which they believed to be work-related. A substantial proportion of this estimate may represent respiratory diseases other than occupational asthma.
• The incidence rate of occupational asthma in 2006 based on reports from occupational and chest physicians contributing to the THOR (SWORD and OPRA) scheme was 20 cases per million workers per year.
• The THOR scheme is subject to underreporting and other evidence suggests that the overall incidence of occupational asthma in Great Britain may be an order of magnitude higher than that based on THOR.
• Statistical modelling by the University of Manchester showed statistically significant downward tends in the incidence of occupational asthma over the period 1996-2006 after taking account of certain factors which affect the annual estimates based on THOR.
• Flour, grain and isocyanates were the most commonly cited agents for occupational asthma in 2004-06 in the THOR and Industrial Injuries and Disablement Benefit (IIDB) schemes.
• The occupations with the highest incidence rate of occupational asthma as reported by chest physicians were ‘bakers, flour confectioners’, ‘metal making and treating process operatives’, and ‘vehicle spray painters’.
• The industries with the highest incidence rate of occupational asthma as reported to chest physicians were the 'manufacture of basic metals' and the 'manufacture of motor vehicles, trailers and semi-trailers'.