Discussion

Our analysis indicates a substantial decline in work-related mortality among men in England and Wales over the last two decades of the 20th century. Nevertheless, occupational activities and exposures continued to account for large numbers of deaths nationally, particularly from COPD, pneumoconiosis, pleural cancer and motor vehicle accidents. Moreover, there was no clear decline in mortality attributable to asbestos, or in deaths from sino-nasal cancer associated with exposure to wood dust. Risk of work-related mortality was particularly high in coal miners and aircraft flight deck officers.

The method by which we assessed the burden of mortality that could be ascribed to work had various limitations, although robust conclusions are possible provided these shortcomings are recognised and taken into account when results are interpreted.

Because no satisfactory data were available on the populations at risk in each job group, we were obliged to base our calculations on proportional mortality. Thus, risk estimates may have been distorted if there were unusually low or high total death rates in occupations of interest. And further error could have occurred through confounding by non-occupational risk factors such as smoking, although this should have been reduced by standardisation of PMRs for social class.

Another possible source of bias was selective recruitment into certain jobs. In particular, the high mortality from alcohol-related diseases among publicans and bar staff, while partly a consequence of their ready access to alcohol at work, is likely to have resulted also from a propensity for heavier drinkers to seek work in bars.7–9 Similarly, the high PMR for viral hepatitis in doctors may not necessarily reflect infection acquired occupationally through sharps injuries but may have occurred because an unusually high proportion of doctors were immigrants from countries with a high prevalence of hepatitis B infection in infancy. During 1982–1990, only five of the 12 male doctors who died from hepatitis in England and Wales had been born in the UK. Of the other seven, four had been born in Africa.1

Other shortcomings may have caused risks to be underestimated. Occupational data were limited to the decedent's last full-time job, but for diseases that develop only after a long induction period (eg, cancers), or that follow a prolonged clinical course before causing death (eg, COPD), causally related occupations will not always be the last that were held before death. It is probably for this reason that some deaths from farmer's lung disease were recorded in non-farmers, and some deaths from coal workers' pneumoconiosis occurred in jobs unrelated to coal mining.

Furthermore, deaths could only be ascribed to occupation where the link could be made with reasonable confidence. Where a causal exposure was not typical of the job group to which an individual belonged, its effect may not have been recognised. For example, work-related death from injury by fire could occur in any occupation, but from the information that was supplied to us, there was no way of distinguishing fires in the workplace from those occurring in other circumstances. Thus, only in fire service personnel did it seem reasonable to attribute excess mortality from injury by fire to work.

In addition, errors are known to occur in the reporting of both occupation and cause of death on death certificates.10 11 In general, such errors would be expected to obscure true associations between occupations and mortality.

There are also statistical uncertainties in our risk estimates, particularly where they were based on only small numbers of observed and expected deaths. Our decision to count the attributable number of deaths as zero where the observed minus expected number was negative, will have introduced a small inflationary bias in estimates of the total burden of mortality attributable to work. However, in practice this situation rarely occurred, and the effect will therefore have been minimal.

Because of these limitations, for some causes of death (eg, many categories of acute injury), other sources of data such as reporting schemes are likely to give more reliable estimates of attributable numbers. For example, notifications to the Health and Safety Executive under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR),12 indicated some 275 deaths per year from fatal occupational injuries in all workers in Great Britain during 1992–2000. Even allowing for the fact that this statistic included deaths in women as well as men, and in Scotland as well as England and Wales, it indicates a larger problem than our figure of 138.9 excess deaths per year during 1991–2000. But for causes of death that cannot confidently be ascribed to occupation in the individual case because their relation to work is not sufficiently specific (eg, COPD in coal miners or lobar pneumonia in jobs involving exposure to metal fume), reporting schemes are unsatisfactory, and the approach that we adopted is the best available.

Our method is likely to have been most reliable in the information that it provided about trends over time, since the biases that have been described can be expected to apply in much the same way in different time periods. In support of this, the fall that we observed in excess deaths from occupational injuries is consistent with a reduction in such deaths reported through RIDDOR.12 The analysis for 1979–1990 included a small number of deaths (121 in total) from uniquely occupational diseases in men with known employment but inadequately described occupations, whereas during 1991–2000 men with inadequately described jobs were grouped with those who had no recorded occupation, and excluded from the analysis. Nevertheless, it seems clear that there was a substantial decline over the period of study in work-related mortality overall, and in that from most specific diseases and injuries. This is likely to reflect both improvements in working conditions and methods, and also a reduction in the number of men employed in more hazardous jobs. For example, the major fall in deaths from COPD attributable to coal mine dust was driven more by lower total numbers of deaths in coal miners than by a reduction in their PMR for the disease, suggesting that contraction of the industry had a bigger effect than improvements in working conditions.

It is notable that the decline in work-attributable mortality did not extend to asbestos-related disease. This accords with earlier analyses of national trends in mortality from mesothelioma,13 14 but it is of concern that there was also no reduction in mortality from asbestosis over the study period. While mesothelioma typically occurs with a long induction period from first exposure to asbestos, deaths from asbestosis are likely to be influenced also by more recent exposures. Our findings therefore reinforce the importance of continuing efforts to ensure that exposures to asbestos are properly controlled. Similarly, the absence of any clear reduction in excess mortality from sino-nasal cancer among wood-working occupations is an indication for further checks on the adequacy of control measures, particularly in furniture manufacture.

Our analysis also highlights a substantial and continuing excess mortality from motor vehicle accidents (principally on-road but also off-road) in lorry drivers. During 1991–2000 this amounted to an average of 38 extra deaths per year with a PMR of 1.75 for on-road accidents. In the UK, prevention of road traffic accidents is the responsibility of the Department for Transport rather than the Health and Safety Executive, and data on work-related road traffic injuries are not therefore included in routine statistics of occupational injuries. The risk that we have identified is unlikely to be an artefact of our analytical method, and should be a spur to analysis of other, more detailed data on accidents involving lorries, as a basis for enhanced, targeted preventive strategies.

Notable also is the high absolute risk of work-related death in certain occupations. In particular, during 1991–2000, excess mortality from COPD, pneumoconiosis and other work-related causes accounted for 4.3% of deaths at ages 20–74 years in ‘other coal miners’, while 4% of deaths among aircraft flight deck officers were from air traffic accidents. The risks of respiratory disease associated with coal mining are decreasing and this can be expected to continue as a consequence of better control of dust levels in recent decades. However, the high risk of accidental death in pilots, which has been noted before,1 and which is likely to result largely from accidents involving smaller aircraft, is a continuing concern. As already discussed, the high risk of alcohol-related deaths in publicans and bar staff is probably determined in part by selective recruitment of drinkers to work in bars, and therefore probably over-represents the risks from such work. In many of the other job groups with apparently high proportional excess mortality, the excess was driven largely by cancer of the bronchus, and may in part have been confounded by smoking.

In summary, we have demonstrated a substantial reduction since 1979 in deaths attributable to work in England and Wales. However, several hazards remain problematic, and are a priority for further preventive action. These include diseases caused by asbestos, sino-nasal cancer in woodworkers, and motor vehicle accidents in lorry drivers.