Underestimating the burden of pertussis in WA 2011 CSTE Annual Meeting Pittsburgh, PA

1. Underestimating the burden of pertussis in WA 2011 CSTE Annual Meeting Pittsburgh, PA Chas DeBolt RN, MPH AzadehTasslimi, MPH Washington State Department of Health

2. Objectives • Compare 2007-2010 PCR-positive suspect cases with confirmedpertussis cases to determine differences in: • Demographics • Measures of severity, outcome & antibiotic use • Symptoms • Estimate sensitivity, specificity, & predictive value of Bordetellapertussis(Bp) PCR assays • WA State Public Health Laboratories (PHL), 2005-2010 • Comparing results with standard culture

3. Case classification* Confirmed • Isolate Bp from clinical specimen +cough of any duration, OR • Detect Bp DNA by PCR + clinical case definition, OR • Link to lab-confirmed case + clinical case definition Probable • Meets clinical case definition but • No Bp isolation or Bp DNA detected by PCR AND • No link to a lab-confirmed case * Only confirmed or probable cases reported to CDC

4. Case classification (2) • Clinical case definition • Cough ≥ 2 weeks PLUSone of following • Cough paroxysms • Inspiratory “whoop” • Post-tussive emesis • Bp PCR in WA • 1999: Bp PCR implemented at PHL • By 2005, Bp PCR widely available at commercial labs

5. Bp Culture & PCR in WA • WA PHL, 2005-2010: • Of 9,623 samples sent for Bp culture, Bp isolated in only 318 (3.2%) • Of 5,369 samples sent for Bp PCR, Bp DNA detected in 422 (7.9%) • Of these, 4,468 (83%) also cultured • 99 PCR results uninterpretable • 4,372 with PCR result & culture result

6. BpCulture Sample Submissions to WA PHL by Year, 2005-2010 * Policy change at PHL to only receive samples whose testing result will be used to make public health decisions

7. Bp PCR Sample Submissions to WA PHL by Year, 2005-2010 * Policy change at PHL to only receive samples whose testing result will be used to make public health decisions

8. Paired Bp PCR & culture results, WA PHL, 2005-2010 * Of these 12, 6 (50%) occurred during a single six-week period in Spring 2009

9. Performance of Bp PCR performance compared to culture • Sensitivity: 87% • Specificity: 94% • PPV: 23% • NPV: 100%

10. Changes in classification method for pertussis cases in WA • 2005: Web-based electronic reporting system (PHIMS) start-up in WA • Allows WA DOH & local health departments to jointly review/classify pertussis cases • Improved classification • 2005-2006: Many PCR-positive pertussis cases that do not meet clinical case definition

11. WA DOH defines “suspect” case • Person whose initial symptoms suggest pertussis • Subsequent testing negative OR no testing done • Cough duration < 2 weeks or cough duration undetermined

12. WA DOH establishes “suspect” case classification • 2007: DOH defines Bp PCR-positive persons that do not meet clinical cases definitions as “suspect cases”* • No two-week cough in a PCR-positive person → “suspect” • For case & contact management, persons should be treated as if they had pertussis • Only confirmed & probable cases are reported to CDC • * http://www.doh.wa.gov/notify/guidelines/pdf/pertussis.pdf

13. Reported pertussis cases in WA, 2007-2010 • Confirmed cases: 1466 (72%) • Probable cases: 375 (18%) • Suspect cases: 194 (10%) Among suspect cases, 81 (42%) Bp PCR-positive

14. Reported pertussis cases in WA by case classification, 2007-2010 * Only confirmed or probable cases reported to CDC

15. Confirmed & PCR-positive suspect cases by age & gender, WA, 2007-2010

16. Confirmed & PCR-positive suspect cases by race, ethnicity & region of residence, WA, 2007-2010 WA

17. Comparing, case-defining symptoms, clinical syndrome & disease severity • Case-defining symptoms (cough, whoop, vomit) • Clinical syndromes • Pneumonia • Encephalitis • Severity • Antibiotic received • ICU Admission • Hospitalized overnight • Case fatality ratio • Chronic lung disease in survivors

18. Comparison of case-defining symptoms by case classification, WA, 2007 - 2010

19. Data completeness for clinically defining symptoms, 2007-2010

20. Comparison of syndrome & outcome by case classification, WA, 2007-2010 * Fisher’s Exact Test, one-tailed

21. Data completeness by case classification, 2007-2010 *

22. Proportion of Total Number of Confirmed & PCR+ Suspect Cases by Quarter of Onset, WA, 2007-2010

23. Proportion of Total Number of Confirmed & PCR+ Suspect Cases by Quarter of Onset, WA, 2007-2010

24. Summary • Increasing use of Bp PCR since 2005 • Bp PCR - 100% NPV for culture isolate • Of 194 suspect cases identified in WA in 2007-10, 81 (42%) associated with positive Bp PCR assay • PCR+ suspect & confirmed cases markedly different symptoms • May be due to incomplete data entry • PCR+ suspect & confirmed cases similar in • Age • Race/ethnicity • Geographic distribution • Clinical syndrome • Severity of illness • Outcome

25. Proposed actions • If available, use Bp PCR result in algorithm to decide if culture should be pursued • Consider inclusion of PCR-positive cases as “probable cases” when 2-week cough, epidemiologic link, or association with an outbreak are not present • For discussion: PHL versus commercial lab results

26. Acknowledgements Dr. Anthony A Tellez-Marfin, Washington State Department of Health Ms. Yolanda Houze, Washington State Public Health Laboratories Dr. Brendon “Troy” Leader, Washington State Public Health Laboratories Health Officers and Disease Investigators of 35 WA State local health jurisdictions

27. Thank you. Questions

28. Documentation of case-defining symptoms for PCR-positive suspect cases 2007-2010 • 23/81 (28%) were missing data for at least one clinical case-defining variable • whoop, vomit, paroxysms, cough duration • For 17/81 (21%) the missing data were key to determining cases classification • 1 record missing all 4 clinical case defining criteria • 4 cases had a cough duration greater than 2 weeks but missing at least one of the other case-defining symptoms • 12 (15%) cases had at least one case-defining symptom, but were missing data for cough duration

29. Reported Pertussis in WA State by case classification 2007-2010