1. Cynthia F. Hinton, PhD, MS, MPH
Pertussis Outbreak in a Highly-Vaccinated School Population–Faulkner County, Arkansas, 2007
Cynthia F. Hinton, PhD, MS, MPH
Presented at the 42nd Annual National Immunization Conference, Atlanta, GA
March 19, 2008

2. Background: Pertussis Outbreak in Faulkner County, Arkansas
Occurred among school children from February 2007
Post-exposure antimicrobial prophylaxis given to contacts
Cases reported through April
Invited by Arkansas State Health Department to assist with investigation on April 24, 2007
Tdap campaign April 27, 2007
Vilonia is a small town north of the state capitol of Little Rock, about a 45 minute drive. Although still considered rural, the town is in one of the fastest growing areas of Arkansas, due to its proximity to Little Rock, and Conway a university town 14 miles west.
Beginning in February 2007, the Vilonia school district in Faulkner county experienced an outbreak of cough illness affecting school-aged children, their families, school faculty and staff.
Contacts received post-exposure antimicrobial prophylaxis, and as the outbreak continued the Arkansas Department of Health planned a Tdap vaccination campaign for the end of April for eligible students, faculty, and staff.
Cases continued to be reported through April and on April 24, 2007, the state invited CDC to participate in an investigation of the outbreak.

3. Objectives Characterize epidemiology of outbreak
Assess vaccine effectiveness
The objectives of our investigation were to characterize the epidemiology of the outbreak and assess vaccine effectiveness in the affected school population.

4. Council of State and Territorial Epidemiologists (CSTE) Case Definitions
Clinical case :
Cough duration ≥14 days
Paroxysms, whoop or post-tussive vomiting
No other cause identified
Probable case
Meets clinical case definition with no laboratory or epidemiologic linkage
Confirmed Case
Cough with any duration and isolation of Bordetella pertussis
Clinical case AND
Positive polymerase chain reaction test (PCR) OR
Epidemiologic-link to lab-confirmed case
In conducting out investigation , we applied the following cases definitions:
Clinical case :
Cough duration ≥14 days plus one of the following symptoms:
Paroxysms, whoop or post-tussive vomiting
No other cause identified
Probable case
Meets clinical case definition with no laboratory or epidemiologic linkage
Confirmed Case
Cough with any duration and isolation of Bordetella pertussis OR
Clinical case AND
Positive polymerase chain reaction test (PCR) OR
Epidemiologic-link to lab-confirmed case

5. Methods
Corroborated PCR results from the Arkansas Public Health Laboratory at CDC Pertussis Laboratory using IS481 and ptxS1 primers
Reviewed pertussis surveillance case records
Accessed school vaccination records for grades K-7
We corroborated PCR results from the Arkansas Public Health Laboratory at CDC Pertussis Laboratory using IS481 and ptxS1 primers
We reviewed pertussis surveillance case records collected by the state, and
We accessed school vaccination records for grades K-7 to assess vaccine efficacy

6. Laboratory Confirmation
23 cases identified with 1-target PCR
CDC corroborated 3 cases with 2-target PCR using IS481 and ptxS1 primers
19 identified by commercial laboratories
14 cases had epidemiologic-linkage
No positive culture
We were able to send samples collected by the Arkansas Public Health Laboratory to the CDC Pertussis laboratory for corroboration by 2-target pcr using IS481 and ptxS1 primers. CDC was able to corroborate 3 of 4 cases identified by the Arkansas Public Health Laboratory.
Nineteen cases were identified by pcr from samples sent to commercial laboratories earlier in the outbreak. The samples were unavailable for further testing.
14 cases were link epidemiologically linked to theses laboratory confirmed cases
Despite best efforts to collect samples via nasal swab and naso-pharyngeal aspirates, our CDC laboratorian was unable to culture bordetella pertussis

7. N = 88 Health Department Tdap campaign Index Case
This slide shows the epidemiologic curve for the outbreak as a whole, which included school children, children under school age, family members, school faculty and staff.
The cough onset of the index case was February 15, This child was not confirmed as a case until her sister tested pcr positive almost 5 weeks later.
The health department identified this as a pertussis outbreak on March 30, which was the first incidence of a macrolide being prescribed for treatment.
The outbreak has a broad peak during the weeks of March 22 through April 5th.
In total, there were 88 occurrences of cough-illness: 42 in grades K-7
15 in grades 8-12 and
31 others, which included children younger than school-age, family members, and school faculty and staff
The red arrow indicates the time of the Tdap vaccination campaign administered to eligible students, faculty and staff (April 27, 2007)
Our investigation focuses on the confirmed cases in the school district, of which there were 37 confirmed cases K-12
N = 88

8. This figure shows the distribution of confirmed pertussis cases, grades K through 12. The week of the outbreak is on the x-axis, the number of cases on the y-axis. PCR confirmed cases are in green and epidemiologically-linked cases in yellow.
N =37

9. Demographics 97% of cases were non-Hispanic White
57% of the cases were female
97% of cases were non-Hispanic White. This reflects the composition of the community.
57% of the cases were female

10. This is the age distribution of the confirmed cases
This is the age distribution of the confirmed cases. The median was nine years of age. The age distribution is also reflected in the attack rate by school.

11. Attack Rate (AR) by School
Grades
# Cases
AR (%)
Primary
K-4
11/504
2.2
Elementary
8/570
1.4
Middle
5-7
10/661
1.5
Junior High
8-9
4/440
0.9
High
10-12
4/667
0.6
The attack rates were highest in grades K through 7. The Primary school (K-4) had the highest attack rate at 2.2%.

12. Distribution of Symptoms Among Cases
Describe slide:
By case definition, 100% of cases had cough.
89% of cases reported paroxyms
47% reported postussive vomiting or gagging
42% reported apnea.
Finally, 16% of cases reported whoop.
The median length of cough was 21 days, with a range from 14 to 59 days.
There were no complications, such as hospitalization or death, among any of the cases.
N = 37

13. Treatment 87% cases treated with recommended antimicrobial agents
Time to treatment pre-outbreak recognition: 14 days
Time to treatment post-outbreak recognition: 6.5 days (p < )
87% of the cases were treated with an appropriate antimicrobial agent, such as one of the macrolides (typically azithromycin) or co-trimoxazole. It took several weeks before it became apparent that the school was experiencing an outbreak of pertussis as opposed to another type of upper respiratory infection.
The average time to from cough onset to start of appropriate antimicrobial was 14 days before recognition of a widespread outbreak. The average time to treatment after recognition was 6.5 days from cough onset. This difference is significant.

14. Vaccination Status by Doses, Grades K-7
Total Dose
Non-cases
Case
AR % ≤2 4 3 19
187 5
2.6
1496 24
1.6
We were eager to explore possible differences in vaccination status, particularly considering the young ages of the affected students.
We looked at vaccination status by number of doses. These were students who were eligible for 5 doses. There were 4 students whose records reported less than 3 doses. These may be students who weren’t still enrolled or up-to-date, because the minimum number of doses for school enrollment required by Arkansas state law is three.
The attack rate for students with 4 doses was 2.6% and the attack rate for students with 5 doses was 1.6%.

15. Time Since Last Dose, K-7 P > .7038 N Days since last dose Cases 29
1783 ± 146.4
Non-cases
1706
1726 ± 30.6
Was there a difference in the time since the last doses between affected and unaffected students?
The days since last does for cases was 1783 days. The days since last dose for non-cases was 1726.
As you can see, there was no significant difference in the time since last vaccination dose.
P > .7038

16. Are Doses Valid? Grades K-7
Invalid Age
Non-cases
Case
Dose 1 5
Dose 2 7
Dose 3
Dose 4
Dose 5 33
Were the doses valid?
We determined that cases had valid vaccination doses.

17. Attack Rate By Vaccination Status, Grades K-7
AR (%)
Vaccinated
29/1506
1.9%
Under-vaccinated
0/229 0%
Which leads us to an attack rate among vaccinated students of 1.9%. There were no cases among under-vaccinated students.
P > 0.7

18. Conclusions Pertussis was the cause of the outbreak
Outbreaks can occur in highly-vaccinated school populations
Recommend continued high levels of vaccine coverage and heightened awareness
Research on disease transmission and resolution of outbreaks is needed
In conclusion:
Pertussis was the cause of the outbreak. This outbreak was very unusual in that it occurred among young school age children and not infants or adolescents.
This serves as reminder that pertussis outbreaks can occur in highly-vaccinated school populations
We recommend continued high vaccination coverage and we see a need for increased awareness of among health care providers.
Lastly, there is still much we do not know about patterns of disease transmission and resolution of outbreaks. Continued research is needed on improved detection --- such as PCR and serology --- and effectiveness of prophylaxis and expanded Tdap coverage.

19. Acknowledgements AR DOH CDC/NCIRD/DBD Linda Gladden Andrew Baughman
Terri Iacobacci
Altino McKelvey
Sandra Snow
AR Public Health Laboratory
Nurses of the Faulkner County Health Unit
Vilonia School Nurses and Administrative Staff
CDC/NCIRD/DBD
Andrew Baughman
Pam Cassiday
Thomas Clark
Nancy Messonier
Eric Stern
Tej Tiwari
Lucia M. Tondella
I would like to acknowledge everyone who contributed to the investigation and to the analysis of these data.
In particular I want to thank the nurses of the County health unit and school nurses who did a tremendous job identifying and tracking cases and helping us obtain the data to conduct this investigation.
The findings and conclusions in this presentation are those of the author and do not necessarily represent the official position of the Centers for Disease Control and Prevention

20. THANK YOU

22. How Many Susceptibles Could Be Expected?
Vaccine Efficacy
85%
Fully vaccinated students
1506
Fully vaccinated but Susceptible
226
Under-vaccinated
229
Total Susceptible
455

23. Are the doses valid? Invalid Interval? Unaffected Case Dose 1 late 1914
Dose 2 14
Dose 3 12
Dose 4 52
Dose 5