PCR, Culture and Serology as Diagnostic Tools for Pertussis in Highly-Vaccinated Children

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PCR, Culture and Serology as Diagnostic Tools for
Pertussis in Highly-Vaccinated Children

• E. Bamberger, M. Jaffe, R. Gershtein, D.
  Benilevi, I. Srugo
• Bnai Zion Medical Center
• N. Lahat, V. Gershtein, S. Shapiro
• Carmel Medical Center
• I. Kassis
• Rambam Medical Center

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Incidence of B. Pertussis in Israel 1967-2001
(Source ICDC)
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Bordetella pertussis Changing Manifestation
Epidemiology

• Pre-vaccine era Classical disease
• Current, vaccine era Disease more protracted
  Atypical
• The incidence of pertussis shows two groups at
  increased risk
• Infants younger than 6 months
• Teenagers and adults

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Reemergence of B. pertussis
Atypical clinical disease
Increased reservoir for transmission
Increased incidence
Limitations of lab techniques
Waning immunity
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PCR Amplifies a Targeted Sequence
Target Sequence
DNA Strand
Double Helix DNA Strand
Supercoiled DNA Strand
Chromosome
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Target Amplification
No. of No. Amplicon Cycles Copies of
Target 1 2 2 4 3 8 4 16 5 32 6 64 20 1,048,576 30
1,073,741,824
1 cycle 2 Amplicon
2 cycle 4 Amplicon
3 cycle 8 Amplicon
4 cycle 16 Amplicon
5 cycle 32 Amplicon
6 cycle 64 Amplicon
7 cycle 128 Amplicon
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PCR Laboratory Diagnosis

• Clinically validated, semi-nested PCR based on
  rapid insertion sequence
• Specificity 96.
• Sensitivity 99

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Objectives

• To compare clinical laboratory diagnostic
  methods used in the diagnosis of B. pertussis
• To examine whether childs immunization status
  matters?
• To examine utility of CDC diagnostic criteria?

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Materials and Methods

• Clinical symptomotology and immunization status
  were collected for 306 patients with suspected
  pertussis between 1999 - 2000
• Two nasopharyngeal swabs were collected for PCR
  and culture.
• Serum specimen for IgM and IgA Bordetella
  pertussis serology

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Stratification of Sample (n240)

• Pre-vaccinated infants
• lt/1 yr (0-1 doses)
• (n87)
• Recently vaccinated children
• lt5 yrs (3-4 doses) or lt/1 yr (2 doses)
• (n78)
• Post-vaccinated children
• 5-18 yrs (4 doses)
• (n75)

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Demographic Profile of Sample
Total number of patients 240
Mean age ( range ) in years 4.1 (.05 to 17.67)
Percent male 49.8
Percent with family cough 47.41
Percent with no previous antibiotic treatment 65.22
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Laboratory Profile of Sample
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(No Transcript)
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Odds Ratios for Clinical Predictors of Positive
PCR (By Group)
Symptom Pre-Vac. Recently-Vac. Post-Vac.
Cough by weeks 0.52 1.83 0.88
Whoop 7.66 1.64 2.3
Paroxysmal cough 1.39 2.27 2.18
Fever 0.38 1.74 1.11
Cyanosis 1.61 2.58 2.76
Vomiting 0.26 0.81 1.53
plt.10 plt.05 plt.001
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Association Between PCR and Cough Among
Pre-vaccinated Subjects
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Case definition for pertussis (CDC)

• Clinical case of pertussis is defined as a cough
  illness lasting at least 2 weeks with either
• paroxysms of cough
• inspiratory whoop
• post-tussive vomiting
• without other apparent cause

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Percent of Missed Diagnosis of Pertussis Applying
CDC Criteria
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Conclusion (1)

• PCR is a useful tool for pertussis diagnosis,
  particularly in pre-vaccinated infants
• The yield of culture and serology is limited,
  especially among pre-and recently vaccinated
  children.

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Conclusion (2)

• As recently- and post-vaccinated children often
  exhibit atypical disease, many may go
  undiagnosed, thus increasing the reservoir for
  transmission
• In pre-vaccinated infants with whoop and lt2 weeks
  of cough, PCR should be preformed promptly
• In Israel, the adoption of a 5th booster dose
  should be strongly considered