The recommendation to use a "dry orange top tube" for PCR testing for pertussis [in "Pertussis:
an avoidable epidemic" BPJ 45 (Aug, 2012)], has caused a bit of confusion.
Laboratories seem to have differing sample requirements and instructions. For example, LabPlus instructions are for
swabs in transport media and Canterbury Health Laboratories request a dry swab only, but have no reference to an orange
The "orange topped tubes" referred to in the Pertussis article are the flock-topped nasal swabs with a flexible head.
This is the recommended swab to use, as the flock top picks up (and releases) more material than the conventional cotton
or Dacron swab, and the flexible head allows for the best chance of correct nasopharyngeal swabbing technique.
A swab which uses a charcoal medium for transport of the specimen is not recommended because a PCR analysis cannot
be conducted on a sample that has been placed in charcoal medium, and the swab will therefore be rejected by the laboratory.
The charcoal swab is used for pertussis culture, which is less useful than PCR as it has a lower sensitivity and a
narrow time frame in which a sample will return a positive result. Pertussis culture is no longer recommended, although
it is still available from some laboratories.
It appears that there are inconsistencies in the type of swab recommended by New Zealand laboratories. Most laboratories
will accept a swab in a dry tube or a tube with universal viral transport medium, regardless of the swab or tube colour.
Wire swabs are also acceptable, as long as the thinner, flexible head wire swab is used. The thicker wire swabs used
for nose or throat swabs are not recommended as they are not flexible enough to be used to take a correct nasopharyngeal
In summary, the three most common swabs that can be used for pertussis PCR testing are:
- The orange top, flock-topped, flexible head swab, with dry tube
- The blue top, wire swab placed back in the dry tube (not in the charcoal medium tube)
- A flock-topped, flexible head swab that is broken off into a short tube with universal viral transport medium
Other types of swab may be available and it is recommended that practitioners check with their local laboratory as
to what the preferred sample method and materials are.
ACKNOWLEDGEMENT Thank you to Dr Margaret (Kitty) Croxson, Clinical HOD, Virology/Immunology,
LabPlus, Auckland City Hospital for expert guidance in developing this correspondence item.