Description of the test
The presence of Bordetella pertussis is confirmed by PCR on respiratory samples, as well as other related Bordetella species. A culture is also systematically performed on the positive samples.
Only B. pertussis is considered in the ECDC case definition of pertussis. Infection with B. parapertussis, which can cause a milder clinical picture similar to whooping cough, is also monitored by Sciensano but does not fulfill the European definition.
PCR for IS481, IS1001, ptxA-Pr and recA is used to demonstrate the presence of Bordetella pertussis and related Bordetella species.
The PCR for IS481 is highly sensitive for detecting B. pertussis but not fully species-specific; this insertion sequence is present in 50 to 200 copies in B. pertussis but also in 8 to 10 copies in B. holmesii and low number in some B. bronchiseptica. The same problem exists for detection of B. parapertussis by IS1001, present in about 20 copies in this species but also in 1 to 7 copies in some B. bronchiseptica.
The PCR for the recA gene is specific for B. holmesii and will cross-react with this species, which can colonize the upper respiratory tract. The PCR ptxA-Pr confirms the presence of B. pertussis or B. parapertussis. However, the latter two PCRs are clearly less sensitive.
Depending on the results for these four targets, the presence of B. pertussis or B. parapertussis is confirmed with certainty or one can only confirm the presence of a Bordetella spp. and specify the most likely species present.
Purpose of the test
- Confirmation of positive molecular tests for B. pertussis is performed by a method that distinguishes it from infection with related species, i.e. B. holmesii, B. parapertussis and B. bronchiseptica, which are not included in the European definition of laboratory-confirmed whooping cough.
- The aim of the culture is mainly to collect a number of isolates for further investigation.
Criteria for performing this test in the context of reference activities
- All respiratory samples found positive in clinical laboratories are accepted for PCR and culture under the NRC activity.
- It is also possible to have a PCR Bordetella performed in the NRC within the framework of reimbursement via Article 24bis of the NIHDI nomenclature, or if the conditions for reimbursement are not met, with billing to the referring laboratory. In this case, please use the ad hoc form of our laboratory guide.
Patients with symptoms of whooping cough:
- Patients aged 1 year and over who have been coughing for less than 3 weeks.
- Children under the age of 1 year with cough, respiratory failure or “sudden infant death syndrome”, regardless of the duration of symptoms.
Instructions for samples
Specimens:
A minimum volume of 500 µl is required for respiratory samples.
Storage:
- PCR: at 4°C for 3 days; (in exceptional circumstances, samples can be stored at -20°C for longer periods).
- Culture: preferably for up to 24 hours at 4°C.
Instructions for transport
Samples are preferably transported to the NRC within 24 hours without refrigeration. Material from the requesting laboratory can be used for this purpose for transport according to UN3373. The NRC does not distribute material.
Unacceptable requests
Indications:
The test within the NRC activity is available only for the confirmation of tests already found positive by a clinical laboratory.
Sample collection:
A minimum volume of 500 µl is required for respiratory samples.
Turnaround time (and frequency of analysis)
PCR:
PCR is performed every working day on samples available at the NRC in the morning. The result is transmitted within 48 hours.
Culture:
Bordetella pertussis grows slowly: the minimum incubation time is 72 hours. A negative result is reported after 12 days of incubation.
Reporting of test results
- By secured electronic mail and by post for positive results.
- By post for negative results.
- Via Medibridge for laboratories and prescribers with a connection to UZ Brussel.