Occupational Asthma

Overall scale of occupational asthma

Prevalence

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 Self-reported Work-related Illness (SWI) module of questions included annually in the national Labour Force Survey (LFS).  Latest results estimate that in 2008/09, 39 000 people who worked in the last 12 months had "breathing or lung problems" caused or made worse by work (with a 95% Confidence Interval: 29 000 to 48 000) [Table SWIT3W12]. 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 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 LFS surveys rely on self diagnosis and responses given therefore depend on lay people’s perceptions of medical matters. As such, these prevalence estimates provide an indicator of the ‘true’ extent of work-related respiratory disease.

Incidence

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 underestimate the overall incidence. A more comprehensive estimate of the total annual incidence of the wider category “breathing and lung problems” is available from the LFS. However because of the limited number of sample cases reporting breathing and lung problems in the LFS it is not possible to consider how the incidence varies by different sub-groups.

In 2008, there were 140 cases of occupational asthma assessed for disablement benefit under the IIDB scheme (Table IIDB01). This compares with 350 cases - a rate of just over 10 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 the order 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 LFS surveys, which in 2008/09 estimated between 12 000 and 26 000 incident cases among those working in the last 12 months, a rate of between 410 and 870 cases per million (Table SWIT6W12). Estimated incidence rates for new diagnoses of respiratory conditions made by participating general practitioners in the new UK surveillance scheme (THOR GP) also show some degree of consistency with these estimates, but less so more recently in 2008, this incidence rate was 190 per million workers, and the average yearly incident rate between 2006 and 2008 was 390 per million workers

Age sex and region

Table THORR03 and Table THORR04 show the distribution of the cases of occupational respiratory disease reported to SWORD and OPRA during 2006-2008 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 just over a quarter of the total. Table THORR04 shows that during 2006-2008, 80 per cent of reported occupational asthma cases were in England, with 13 per cent in Scotland and 7 per cent in Wales.

Other information from reports by GPs

The total number of diagnoses of work-related ill health recorded by participating general practitioners in the new UK surveillance scheme (THOR GP) in 2008 was 1318, of which 17 (1.3%) were respiratory conditions. This compares with a total of: 1560 diagnoses in 2006 (the first year of the scheme), of which 54 cases (3.5%) were respiratory conditions; and 1460 diagnoses in 2007, of which 41 (2.8%) were respiratory conditions. Respiratory diagnoses were less likely to be issued with a sickness notification and tended to be associated with shorter periods of sickness absence than average for all diagnoses (see Table THORGP01, THORGP02, THORGP03, THORGP04, THORGP05, THORGP06, THORGP07)