Health and Safety
Executive / Commission
Statistics
Estimates of the prevalence of occupational illnesses in Great Britain – meaning the total number of people ill at any given time – may be derived from the national surveys of Self-reported Work-related Illness (SWI). From the latest survey, it was estimated that in 2006/07 142 000 people who have ever worked had "breathing or lung problems" caused or made worse by work (95% Confidence Interval: 125 000-159 000) [Table SWIT3]. This estimate is likely to include substantial numbers of individuals with respiratory diseases other than occupational asthma such as Chronic Obstructive Pulmonary Disease (COPD). The 1995 SWI survey collected more detailed information about diseases categories and about 70 percent of those reporting work related lower respiratory disease described symptoms consistent with asthma2. The SWI surveys rely on self diagnosis and responses given therefore depend on lay people’s perceptions of medical matters. As such, these prevalence estimates cannot necessarily be taken directly as an indicator of the ‘true’ extent of work-related respiratory disease.
Two data sources provide information about annual incident (meaning newly diagnosed) cases of occupational asthma in Great Britain: the Department for Work and Pensions (DWP) Industrial Injuries and Disablement Benefit (IIDB) scheme and The Health and Occupation Reporting (THOR) network. Though these sources provide useful information about high risk occupations and particular causal agents for occupational asthma, both are subject to underreporting and therefore tend to underestimate the overall incidence.
In 2006, there were 160 cases of occupational asthma assessed for disablement benefit under the IIDB scheme (Table IIDB01). This compares with 592 cases – a rate of about 20 per million workers per year – recorded by respiratory and occupational physicians reporting to the SWORD and OPRA schemes within the THOR network (Table THORR01). A number of factors may account for the differences between these figures. Individuals may be unaware of the IIDB scheme, and it may tend to pick up fewer cases arising from substances or in occupational settings where the link with asthma is less well established or well known. Furthermore, the self-employed are not covered by the IIS and level of compensation available for even those who are severely disabled may not provide sufficient incentive for all eligible individuals to apply.
A previous review of the data suggested that SWORD may underestimate the true incidence of consultant-diagnosed asthma by at least a third3. Moreover, as many cases of occupational respiratory disease will not be referred to a consultant physician, the total incidence of the disease is likely to be substantially higher. Indeed, proportions of cases of asthma attributed to workplace exposures estimated from epidemiological studies suggest the incidence may be an order of magnitude higher. For example, a recent European population-based study estimated the incidence of occupational asthma (including irritant-induced occupational asthma) to be 250-300 cases per million people per year4 and other studies have estimated that occupational factors account for approximately 9-15% of asthma cases in adults of working age5. Applying these latter proportions to the estimated incidence of adult asthma from a recent review (about 5 cases per 1000 person-years)6 would imply rates of occupational asthma in Great Britain of 450-750 per million workers per year.
There is some uncertainty about whether estimates based on studies in other countries are directly applicable to the Great Britain population. However, these estimates are of the same order as those for the incidence of "breathing or lung problems" from the British SWI surveys, which in 2006/07 estimated between 8,000 and 20,000 incident cases among those working in the last 12 months, a rate of between 270 and 670 cases per million (Table SWIT6W12).
Table THORR03 and Table THORR04 show the distribution of the cases of occupational respiratory disease reported to SWORD and OPRA by age and by country, respectively. The most common age groups for new cases of occupational asthma were 35-44 and 45-54 years – each accounting for around one-quarter of the total. Table THORR04 shows that 83 per cent of reported occupational asthma cases were in England, with 9 per cent in Scotland and 7 per cent in Wales.
Over 1500 of new diagnoses of work-related ill health were made by participating general practitioners in the first year of a new UK surveillance scheme (THOR GP). Of these, 3% were respiratory diseases (Table THORGP01).