Archive Issue

2011, Volume 22, Number 1

FAST FACTS: Pertussis Testing

By D. L. Wiedbrauk, Ph.D.

WML_FastFacts_Pertussis-Testing.pdf

Fast Facts — Pertussis Testing

Recommended Screen – Pertussis PCR Panel (BORDPCR)

This PCR panel utilizes the multi-target detection approach recommended by the Centers for Disease Control and Prevention. PCR targets include real-time PCR testing for the IS481 gene of B. pertussis, the pIS1001gene from B. parapertussis, and the hIS1001 gene from B. holmseii. Reflex testing for the pertussis toxin gene is used as needed to detect dual infections with B. parapertussis and B. holmseii. The analytical sensitivity of this panel is approximately 3 colony forming units/assay.
The clinical sensitivity of PCR testing has been reported to be 70-99% with specificities of 80-100%.
The best specimen for PCR testing is an NP swab tipped with Rayon or Dacron (not cotton) or a nasal aspirate.
Throat and anterior nasal swabs are not acceptable because they provide unacceptably low rates of detection
Do not submit specimens in Regan-Lowe Medium.
B. pertussis can be detected in young children with pertussis for 3 or more weeks after treatment.
The utility of repeat testing to assess treatment efficacy is questionable.
Optimal specimen timing for PCR testing is 0-3 weeks after the onset of cough.
In infants and unvaccinated individuals, an accurate diagnosis may be made for up to 4 weeks after symptom onset.
Persistence of B. pertussis DNA in untreated adults and vaccinated individuals is variable.
Indeterminate results can occur and when present, they may represent a mixed infection, low level positive results in one or more assays, or reactivity patterns that do not match expected values. Retesting may be indicated in these cases.
Cross reactions can occur when the specimen contains high levels of Bordetella bronchiseptica.

Bordetella pertussis Culture (BORD)

Cultures are slow, requiring 7-10 days for a negative result. Positive cultures can usually be resulted in 4-7 days.
Culture sensitivity is 12-60% but the test is very specific.
The highest
sensitivity
occurs
:
When specimens are collected within first 2 weeks after cough onset. In young patients

In unvaccinated patients

When specimens are collected before antibiotic
treatment
If the specimen cannot be plated immediately, it must be placed into Regan-Lowe transport medium.

Bordetella pertussis Antibody Testing (BORDABAR)

Serologic assays can be useful for confirming diagnosis, especially during suspected outbreaks.

Generally, serologic tests are more useful for diagnosis in later phases of the disease.
For a single point serology, the optimal timing for specimen collection is 2 to 8 weeks following cough onset, when the antibody titers are at their highest; however, serology may be performed on specimens collected up to 12 weeks following cough onset.

Bordetella pertussis DFA (BPDFA)

DFA testing is not recommended because the procedure lacks sensitivity and specificity.