Objectives: The ability to measure temporal trends in disease incidence is important but valid methods are needed. We investigated UK trends during 1996-2005 in work-related skin and respiratory diseases including non-malignant pleural disease, asthma, mesothelioma and pneumoconiosis and the potential for bias when using surveillance systems for this purpose.
Methods: The volunteer reporters in three surveillance schemes were specialist physicians for skin diseases, respiratory diseases and occupational physicians respectively, who provided monthly reports of new cases of disease which they considered work-related. Poisson regression models were used to investigate variation by calendar year (trend), season and reporter characteristics. Separately, temporal patterns in the probabilities of non-response and zero reports were investigated. Annual changes in disease incidences were compared between reporter groups.
Results: There was little evidence of change in incidences of non-malignant pleural disease, mesothelioma, skin neoplasia and urticaria but falls were seen for contact dermatitis and pneumoconiosis. Although the direction of changes were similar across reporter groups, the magnitude of annual change in incidence was often not consistent: for occupational asthma, it was -1.9% (95% CI: -5.2,1.4) and -12.1% (95% CI:-19.5,-4.1) using respiratory and occupational physician reports respectively. Response rates were high (~85%) but non-response increased slightly with membership time, as did the probability of a zero return in some groups. Adjustment of results for presumed reporting fatigue led to an upward correction in some calendar trends.
Conclusions: Some estimated changes in incidence based on volunteer reporting may be biased by reporting fatigue; therefore apparent downward trends need to be interpreted cautiously. Differences in the population bases of the surveillance schemes and UK health service capacity constraints may also explain differences in trends found here. (277 words)