Jeremy Beach, Igor Burstyn, Nicola Cherry Occupational Medicine Program University of Alberta

1. Using database linkage to estimate the incidence of new onset adult asthma in Alberta and British Columbia Jeremy Beach, Igor Burstyn, Nicola Cherry Occupational Medicine Program University of Alberta OEMAC, October 2010

2. Occupational asthma • Common; costly; preventable • If not recognised then may be poorly managed • Probably under-diagnosed • Alberta WCB 131 cases 1995 – 2004 • WorkSafe BC mean 59 cases/year 1995 - 2004 • Surveillance • increase local intelligence (where, who, how much?) • focus intervention • demonstrate effectiveness of control measures • Use new onset adult asthma (NOAA) – but no single data source • Occupation • Exposure • Diagnosis

3. Objectives • Already used data linkage with Alberta data1. • To extend the same data linkage technique used in Alberta (AB) to British Columbia (BC). • To compare results for the two provinces. 1Cherry et al, AJIM 2009;52:831

4. Source of data • Identify all WCB claims in 1995-2004 • Source of occupation and industry data (reason for claim irrelevant) • Identify all claims with unique identifier allowing linkage to health data (Personal Health Number (PHN) or similar) • Link to administrative database of Physician billing using PHN • Source of diagnostic data - NOAA • Need to ensure person resident

5. Definition of NOAA • Resident in province for four years prior to WCB claim • Physician billing for asthma (ICD9 493) in 12 months prior to WCB claim • No physician billing for asthma in preceding three years – prevalent cases • Restricted to non-prevalent subjects - if prevalent not at risk of NOAA

6. Alberta • 1,320,792 WCB claims 1995-2004 • 782,908 eligible for matching • 561,951 with occupation recorded. • 349,999 with industry recorded. • Collapse to groups with >250

7. British Columbia • Approx 240 million physician billing episodes 1991-2004 • 3,268,114 WCB claims 1995-2004, • 1,118,239 WCB claims eligible for matching • Two different occupation codes used • 333,132 with valid SOC91 code • Industry coded using CU number

8. Comparison of AB and BC claims

9. Similar occupations with increased risk in AB and BC (adjusted for age and sex)

10. Similar occupations with increased risk in AB and BC (adjusted for age and sex)

11. Occupations with increased risk in either AB or BC (adjusted for age and sex)

12. Similar industries with increased risk in AB and BC (adjusted for age and sex)

14. Occupations and Industries with decreased risk in either AB or BC (adjusted for age and sex)

15. Discussion • This data linkage technique worked in BC as well as AB despite differences in data formats. • Need to be some caution when interpreting these data: • Relatively sensitive case definition – possibility of diagnostic errors. • Errors in identifying occupation – ? job change possible if work-related. • Only a sample of population – WCB claimants – possible bias. • Ease of access to physician/availability of sickness absence • Overall incidence levels appear similar in the two provinces: • if 5-25% of NOAA is occupational asthma suggests WCB claims may be a significant underestimate (average 13-14 per year in Alberta, 59 per year in BC). • Occupations at risk show some similarities and differences between provinces - may reflect differences in exposures. Linkage to JEM. • Some unanticipated occupations appear at risk – raises possibility of heightened surveillance.

16. Acknowledgements • Alberta WCB • Alberta Health and Wellness • BC Linked Health Database • Allergen NCE

18. Similar occupations with increased risk in AB and BC (adjusted for age and sex)