Table 4.

Interpretation of real-time PCR algorithm during pertussis outbreaks

Result for:Interpretation
IS481pIS1001ahIS1001aptxS1a
CT < 35NegativeNegativePositive or negativeB. pertussis
35 ≤ CT < 40NegativeNegativeNegativeIndeterminateb
PositiveNegativePositiveNegativeB. holmesii
NegativePositiveNegativePositiveB. parapertussisc
NegativeNegativeNegativePositiveB. bronchisepticad
  • a A CT of <40 is considered a positive reaction; a CT of ≥40 is considered negative.

  • b Requires confirmation by other means (culture, serology, or epidemiological linkage).

  • c A specimen positive for pIS1001 may be considered to most probably contain B. parapertussis, but the possibility that it is positive for B. bronchiseptica cannot be totally excluded.

  • d Of the human-derived B. bronchiseptica isolates, 64.4% were positive with ptxS1.