1. California 2010 Pertussis Epidemic
Kathleen Winter, MPH, Kathleen Harriman, PhD, MPH, RN, Jennifer Zipprich, PhD, Robert Schechter, MD, John Talarico, DO, MPH
Immunization Branch
California Department of Public Health

2. Overview Pertussis Background California Pertussis Epidemic
Challenges and Success
Ongoing Efforts
Questions

3. Pertussis Background
Pertussis is one of the most poorly controlled vaccine-preventable diseases
Incidence increasing since the 1990s
Cyclical with peaks every 2-5 years; last prior peak year was 2005 with 25,616 U.S. cases, a 45 year high at the time
Very contagious: basic reproduction number (Ro) estimate is 12-17; approximately 80% of susceptible household contacts become infected
Minimum proportion of population that must be immune to eliminate transmission estimated to be 92-95%
* Weiss and Hewlett. Ann Rev Microbiol. 1986;40:661-86

4. Pertussis Background, continued
Adults are vulnerable to pertussis
25% of reported cases are among adults
Pertussis immunity is not lifelong and wanes 4-12 years after the DTaP series and 4-20 years after natural infection*
~20% of cough illness lasting >2 weeks is pertussis
Tdap licensed in 2005, but uptake suboptimal – in 2008 ~6% of U.S. adults were estimated to have ever received Tdap
Adults with pertussis often report feeling as if they’re choking on something, sweating episodes
*Wendleboe et al. Ped Infect Dis J 2005;24 (Suppl 5):S58-61.

5. Pertussis resurgence since the 1990s
Genetic changes in B. pertussis; greater virulence?
Variable vaccine efficacy – acellular vaccines licensed in 1991 for 4th/5th doses, entire series in 1996; estimates of vaccine efficacy for DTaP typically range from 75-85% depending on the case definition that is used
Waning of vaccine-induced immunity
General availability
of better laboratory tests

6. Number of reported pertussis cases by year of onset ― California, 1914-2010*
* Includes cases reported to CDPH as of 3/9/2011

7. Case counting
CDC/CSTE case definitions for ‘Confirmed’ and ‘Probable’ cases
‘Suspect’ case defined as a person with acute cough illness of any duration with:
detection of B. pertussis-specific nucleic acid by PCR; or
at least one of the following: paroxysms, whoop or post-tussive vomiting who is epi-linked to a lab-confirmed case
Case classification breakdown:
61% Confirmed
18% Probable
21% Suspect

8. Number of reported pertussis cases by year of onset -- California 1945-2010*8

9. Epidemic curve of pertussis cases
Epidemic curve of pertussis cases* by week of onset -- California, January 1, 2010 through January 31, 2011

10. Pertussis cases by month of onset -- California, January 2005 - February 2011*

11. Proportion of pertussis cases diagnosed by culture and PCR -- California, 1990-2010*

12. Bordetella pertussis PCR percent positive by week - Southern California Kaiser, July -- December 2010

13. Pertussis cases/rates by age and race/ethnicity ― California, 2010*
Overall rates all ages: White: 21.2/100,000 Hispanic: 26.8/100,000 API: 7.0/100,000 Black: 10.5/100,000
White: 20.3/100,000 Hispanic: 25.7/100,000 API: 6.5/100,000 Black: 9.8/100,000 13

14. Pediatric pertussis rates by age and race/ethnicity ― California, 2010*14

15. Infant pertussis cases by age in months and race/ethnicity ― California, 2010*

16. 2010 Pertussis Hospitalizations as of 3/21/2011
667 (9%) cases are known to have been hospitalized (of the 86% with known status)
Most 480 (72%) hospitalized cases were infants <6 months of age; 362 (54%) were <3 months of age
50% of infants <3 months of age were hospitalized
367 (76%) of the hospitalized infants <6 months of age were Hispanic
~50% of CA birth cohort is Hispanic
Some have had co-infections (RSV/adenovirus/ influenza), which can confuse the diagnosis

17. 2010 Pertussis Deaths
10 deaths; 9 Hispanic infants, 1 White (30 deaths were reported in 1950)
The overall case fatality rate among infant cases <3 months of age is 1.4%
Most (9) were infants <2 months of age at time of disease onset who had not received any doses of pertussis-containing vaccine
One death occurred in a former preemie who received the first dose of DTaP at 2 months of age, 15 days prior to disease onset, and had 3 older siblings with cough illness
Many of the fatal cases had multiple contacts with healthcare providers before pertussis was diagnosed, several had family members with cough illness

18. California Pertussis Deaths
All CA pertussis deaths (~3/year) since 1996 have been in infants <3 months of age
80% Hispanic
Of those with known status, all had pneumonia and pulmonary hypertension
Pertussis toxin elicits a dose-dependent leukocytosis; the mean WBC of fatal cases in was 75,000 (range 15, ,000)
Increases in leukocyte mass can diminish blood flow by increasing vascular resistance; some experts recommend exchange transfusion to lower the WBC and possibly reduce pertussis toxin

19. Pertussis cases in children and adolescents aged 0-18 years with known vaccine history ― California, 2010*

20. Why are so many cases vaccinated?
100 adolescents exposed to pertussis
53 Vaccinated
47 Unvaccinated




53% Tdap coverage
66% vaccine efficacy
80% attack rate among susceptibles
14 vaccinated cases
38 unvaccinated cases
Tdap coverage 53%
Tdap efficacy 65.6%
Secondary attack rate 80% among susceptibles


14/52 (27%) cases are recently vaccinated
Does not take waning immunity into account

21. Why are so many cases vaccinated?
100 children 4-10 years old exposed to pertussis
93 Vaccinated
7 Unvaccinated


93% 5+DTaP coverage
85% vaccine efficacy
80% attack rate among susceptibles
Tdap coverage 53%
Tdap efficacy 65.6%
Secondary attack rate 80% among susceptibles
11 vaccinated cases
6 unvaccinated cases


11/17 (65%) cases are recently vaccinated
Does not take waning immunity into account

22. Challenges
Gaps and implementation barriers in ACIP vaccine recommendations
Clinical recognition, diagnostic and reporting challenges
Effective outbreak control strategies
Prophylaxis recommendations
Targeted vs. community-wide vaccination strategies
Primary goal: to prevent deaths (and hospitalizations) in young infants

23. CDPH Tdap Recommendations July 2010
Immunize pre-teens, teens and adults with Tdap vaccine
underimmunized 7-9 year olds
those >10 years of age who have not yet received Tdap, especially
women of childbearing age, preferably before, or else during or immediately after pregnancy
others with close contact with young infants
includes persons >64 years of age
No minimum interval between Td and Tdap

24. Tdap for Healthcare Personnel
Per the CalOSHA aerosol-transmissible disease standard, employees who may be exposed to aerosol-transmissible diseases must be offered Tdap free of charge if they haven’t already received it
Susceptible employees must also be offered measles, mumps, rubella, and varicella vaccines and all employees must be offered influenza vaccine each year
Employees should be offered Tdap unless they can provide written documentation of a prior dose
No minimum interval between the last dose of Td and Tdap

25. Pertussis Mitigation: Cocooning
256 birth hospitals in California; birth cohort is ~500,000/year
Survey conducted in April 2010 – only 30% had a postpartum Tdap vaccination policy
Primary barrier reported was cost of the vaccine
Tdap Expansion Program developed
Offered free (ARRA-purchased) Tdap vaccine to birth hospitals to establish cocooning programs
70% of birth hospitals enrolled
>71,000 doses administered
Also offered Tdap vaccine to Community Health Centers for cocooning
525 facilities participated
>112,000 doses administered

26. Pertussis Mitigation: Vaccination
Tdap use encouraged in Emergency Departments for wound management
Reimbursement barriers for Tdap vs. Td
Worked with payers re: Tdap reimbursement
Medicare Part D for adults >64 years of age
Encouraged use of accelerated DTaP schedule for infants with first dose at 6 weeks of age

27. Pertussis Mitigation: Provider education
Clinical recognition – pertussis signs and symptoms
Specimen collection and laboratory testing
Treatment recommendations for young infants

28. Pertussis Mitigation: Public education
Vaccination/cocooning
Pertussis signs and symptoms
Infants at greatest risk - keep ill people away from infants

29. Effective Outbreak Control Strategies
Appropriate use of antibiotics for treatment / prophylaxis
Cocooning vs. community-wide vaccination

30. Antibiotic Treatment/Prophylaxis
Treatment generally only useful if started very early in course – during catarrhal stage
Prophylaxis
Identifying contacts difficult
Long infectious period
Large Ro
Prophylaxis not effective until at least 5 days
Typically targeted only to those at highest risk of severe disease or those in contact with high risk people (infants)

31. Cocooning vs. Community-wide Vaccination
No good studies exist to demonstrate efficacy of using a cocooning strategy or of increasing vaccination rates using a community wide approach
Herd immunity levels required >90%
Only 6% of adults with Tdap coverage leaving a very large pool of susceptibles
Cocooning has following advantages:
Targeted use of resources
Family members most likely to transmit to vulnerable infants so may prevent transmission to those at highest risk for morbidity and mortality

32. Community Vaccination – Natural Experiment
New school law effective academic year
All students entering 7-12th grades in required to have a dose of pertussis-containing vaccine
All subsequent years, newly entering 7th grade students will have pertussis vaccine requirement
Affects ~3 million adolescents in California
Current Tdap coverage estimated at 53%
Will this help reduce community transmission?

33. Data: British Columbia Centre for Disease Control

34. Acknowledgements
Many thanks to: Our partners at the 61 California Local Health Jurisdictions CDC – Meningitis and Vaccine-Preventable Diseases Branch and Epi Aid teams