Dutch experience in evaluating syndromic surveillance (SS): a retrospective study

1. Dutch experience in evaluating syndromic surveillance (SS): a retrospective study Cees van den Wijngaard, Liselotte van Asten, Wilfrid van Pelt, Hans van Vliet, Marion Koopmans

2. Retrospective study on SS Objective • Evaluate added value of SS for EW of emerging infectious diseases • For advice on implementation • 1st Research question • Does SS data reflect known common pathogen activity? • Implies SS reflects emerging pathogen activity as well Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

3. Phases of Disease vs Surveillance data Syndromic data (no specific diagnosis) Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

4. Phases of Disease vs Surveillance data Syndromic data (no specific diagnosis) Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

5. Phases of Disease vs Surveillance data Syndromic data Traditional surveillance Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

6. Syndrome data for evaluation • Syndrome choice  Respiratory • Syndrome data  6 existing medical registries • Absenteeism Work absenteeism (no medical information) • GP-consults Infectious disease diagnoses • Pharmacy medications Medications indicative for infections • Lab submissions Diagnostic test requests indicative for infectious disease • Hospital admissions Infectious disease diagnoses • Mortality Infectious disease diagnoses • Syndromes defined by experts and CDC-definitions • Retrospective data over 1999-2004 • Postal code/age/gender • Evaluated as if real-time available Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

7. Does SS reflect common pathogen activity* ? • Data aggregated by week • Plots of syndrome and pathogen lab counts** • Univariate correlation Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

8. Does SS reflect common pathogen activity* ? • Multivariate lineair regression models • Explain syndrome time series by pathogen lab counts** • Syndrome (t) = β0 + β1 Pathogen + β2 Pathogen + …. (eg influenza) (eg RSV) • % of syndrome explained by pathogen activity * counted in labsurveillance ** appropriately lagged (-5 to +5 weeks) Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

9. Syndrome time series explained by pathogen lab counts  84% of syndrome explained by pathogen counts Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

10. Respiratory syndromes explained by pathogen counts All syndromes will probably reflect (emerging) respiratory pathogen activity! Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

11. Validation of regression results • Sine/cosine terms • Correction for coincidental seasonal association between pathogens and syndromes*** • Syndrome (t) = β0 + β1 Pathogen + β2 Pathogen + …. sine(k2πweek/52) + cosine(k2πweek/52) (k=1,2,3)  Associations on Pharmacy and Absenteeism data should be confirmed by research on longer time series Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

12. Difference in timeliness between registries:Optimized lagged correlation of all registry syndrome time series 2 weeks difference Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

13. 3) Difference in timeliness between registries:Optimized lagged correlation of all registry syndrome time series Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

14. Conclusions SS data • These syndromes reflect resp.pathogen activity • Most likely emerging pathogen activity reflected as well • Hospital possibly combines good timeliness and medical information • Other SS research questions • Gastro pathogens? • Can (local) outbreaks be detected with SS? • Can shifts in virulence be detected with SS (influenza)? • Can health burden for common pathogens be estimated with SS (norovirus)? • Combined syndromic and pathogen surveillance? Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten

15. Acknowledgments • Data providers • Statistics Netherlands (CBS) • Foundation for Pharmaceutical Statistics (SFK) • Dutch National Medical Register (LMR) • National Information Network of GP’s (LINH) • Virologic Weekly Returns Surveillance • More information: Kees.van.den.wijngaard@rivm.nl Liselotte.van.asten@rivm.nl Syndromic surveillance evaluation|Cees van den Wijngaard & Liselotte van Asten