Nasopharyngeal swabs or aspirates are the specimens of choice for the recovery of B. pertussis. Aspirate samples are easier to obtain from infants and young children, leading to better organism recovery rates. Nasopharyngeal swab samples must be obtained by trained personnel and are generally used for older children, adolescents, and adults. The swab tip should be a polyester material such as Dacron®, rayon which is similar to cotton but made from a synthetic spun fiber that doesn't damage the specimen, or it could be nylon-flocked. Cotton contains substances that will not only interfere with nucleic acid amplification tests (NAAT) but may also inhibit the growth of B. pertussis (if a culture is ordered). Calcium-alginate swabs and aluminum shafts can also inhibit NAAT detection methods.
The swab should be inserted far enough into the nasal cavity to touch the posterior nasopharynx (see diagram below). This contact should initiate coughing by the patient, but if not, the patient can be prompted to cough to obtain the best clinical specimen. While coughing is not required, it may increase the recovery of the bacteria since it colonizes the ciliated epithelial cells of the upper respiratory tract. Coughing helps release the bacteria from the cilia. If possible, two nasopharyngeal samples should be collected, one from each nostril.
If it is not possible to immediately plate the specimen for culture, the swab(s) should be placed into the appropriate transport medium. The transport medium may vary depending on the testing laboratory and the testing performed. Usually, the requirement is charcoal-containing transport media, such as Amies with charcoal. Regan-Lowe transport medium may be used if only a culture is ordered, but it may interfere with some NAAT methods. It is important to verify the appropriate transport media with the testing laboratory.
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A video that demonstrates proper specimen collection is provided by the Centers for Disease Control and Prevention (CDC) and is available at:
5. Centers for Disease Control and Prevention. Image: Manual for the Surveillance of Vaccine-Preventable Diseases, 2015.
