1. Counting Chronic Hepatitis B cases in York Region: Denis Heng York Region Community and Health Services APHEO Conference - “Explaining the Miracle: Statistics and October 15, 2007 Analysis in Public Health”

2. Infectious Diseases Surveillance Unit (IDSU) Component of the Infectious Diseases Control Division, Community and Health Services. Tasked with coordinating surveillance and school immunization programs with the objective of controlling infectious diseases within York Region.

3. "Greetings! I am the Count. Do you know why they call me the Count? Because I love to count things!"

4. Hepatitis B Globally, it is estimated that: –~2 billion have been infected with hepatitis B virus –>350 million have chronic (lifelong) infections Highly endemic (>8% prevalence) in certain areas of the world –East and Southeast Asia, Sub-Saharan Africa A reportable disease in Ontario

5. Estimating HBV Carriers in Canada Canadian Population Hepatitis B carriers N =29,839,030598,103 Immigrants18.4%54.7% Aboriginals3.3%6.5% Canadian-born 78.3%38.8% Source: Sherman et al. Can J Gastro 2007; 21(Suppl C)

6. Background York Region Health Services converted from the Reportable Disease Information System (RDIS) to integrated Public Health Information System (iPHIS) in June 2005 Example of Duplicate Record: Client A lives in Toronto and is diagnosed with hepatitis B in 1993; Toronto Public Health creates an RDIS record with an episode date of 1993;

7. Background Example of Duplicate Record (cont’d): Client A moves to York Region in 2003 and a subsequent hepatitis B lab slip is forwarded to York Region Health Services as a result of regular lab testing. York Region creates an RDIS record with an episode date of 2003; July 2005: RDIS conversion to iPHIS – Client A now has two iPHIS entries for hepatitis B – one 1993 entry attributed to Toronto and one 2003 entry attributed to York Region.

8. Purpose Examine the extent to which York Region chronic hepatitis B incidence data is affected by duplicate records resulting from the merger of Ontario’s 37 RDIS platforms.

9. Methods Cognos line lists were created –Includes all iPHIS entries that have York Region as either the Responsible or Diagnosing Health Unit A manual name search on each of these individual records was performed to identify any duplicate entries in iPHIS.

10. Number of Confirmed Chronic Hepatitis B cases in York Region, Pre- and Post-Validation (2005-2006)

12. Number of Confirmed Chronic Hepatitis C cases in York Region, Pre- and Post-Validation (2005-2006)

13. Ratio of pre-validated to post-validated counts of chronic hepatitis B cases in York Region by month (2005-2006) 2005 January1.66 February2.29 March2.32 April2.16 May1.97 June1.67 July1.65 August1.68 September1.76 October1.79 November1.38 December1.26 2006 1.04 1.09 1.32 1.18 1.08 1.05 1.00 1.03 1.09 1.03 1.07 1.09

14. Percentage of Duplicate Records by Health Unit in 2005 368 duplicate records identified in 2005 (339 clients) ~8% had more than one duplicate record

15. Reasons for Duplication – post RDIS Clients using multiple common names that were not recorded during the initial investigation. –E.g., Record 1 is listed as Ricky Chan; Record 2 is listed as Sai-Kee Chan; Inversion of month/day fields when recording date of birth from source documents. –E.g., First DOB is 1977-07-06; Second DOB is 1977- 06-07; and Typographic errors in the spelling of family names due to partially legible source documents. –E.g., John Paur VS John Paun

16. Conclusion Incidence counts of chronic hepatitis B cases in York Region before 2006 are significantly overestimated due to duplicate records produced in RDIS As such, the 2005 counts validated as part of this study, and 2006 disease counts reflect the most accurate data available at this time for estimating the burden of disease of new chronic hepatitis B cases in York Region.

17. Implications Overestimate of provincial counts Affect counts in other health units –GTA health units Are other reportable diseases overestimated?

18. Acknowledgements Hepatitis B/C Team – York Region Health Services –Case investigators –Administrative staff All other YRHS staff that have contributed to this project Questions?