Laboratory Testing for Pertussis

Key points

• Clinical laboratories can provide diagnostic testing for pertussis.
• Culture is considered the gold standard.
• Other tests that can be performed include polymerase chain reaction (PCR) and serology.
• Learn the optimal time to perform each test method when diagnosing pertussis.

Test methods

Clinical laboratories commonly use several types of diagnostic tests to identify Bordetella pertussis:

• Culture
• PCR
• Serology

Described below are advantages and disadvantages for each test method.

Important consideration

Interpret PCR results with clinical symptoms and epidemiological information. In the setting of an outbreak, culture confirmation of at least one case should occur. Follow simple PCR best practices

Optimal timing for diagnostic testing

Described below is the optimal time to perform each test method.

Culture

• Can be performed during first 2 weeks of illness following cough onset when viable bacteria are still present
• Sensitivity decreases after the first 2 weeks, which increases risk of false-negative results

PCR

• Can be performed up to 3 to 4 weeks following cough onset
• After fourth week of cough, amount of bacterial DNA in nasopharynx rapidly diminishes, increasing risk of a false-negative result

Serology

• Use 2 to 8 weeks following cough onset for optimal results due to highest antibody titers
• Can be performed up to 12 weeks following cough onset, but may be less reliable

CDC serologic test

CDC and the Food and Drug Administration developed a serologic assay that has been useful for confirming diagnosis, especially during suspected pertussis outbreaks. A few state public health laboratories have included this assay as part of their testing regimen for pertussis. This assay is also available for research or surveillance purposes through CDC's test directory.

CDC evaluation of commercially available assays

Commercially, there are several different serologic tests used in the United States with unproven or unknown clinical accuracy. CDC performed an evaluation of several commercially available assays in the United States and found great variability between them, depending on the antigen or antibody used and whether they were calibrated to an international reference serum. Analysis found the most promising assays were those that measured IgG antibodies against pertussis toxin only and were calibrated to a reference standard.

Obtaining a nasopharyngeal (NP) swab or aspirate

Healthcare providers should obtain an NP swab or aspirate from everyone with suspected pertussis.

Using specimen for culture

Directly plate collected NP specimen or immediately place into transport medium. Plating should occur within 24 hours of NP swab or aspirate collection.

Pertussis Testing Video: Collecting a Nasopharyngeal Swab Clinical Specimen

Pertussis Testing Video: Collecting a Nasopharyngeal Aspirate Clinical Specimen

Proper technique for obtaining an NP specimen for isolation

A properly obtained NP swab or aspirate is needed for optimal diagnostic results. The same specimen can be used both for culture and PCR.

Specimen acceptance criteria

Public health laboratories and other federal agencies can submit specific specimen types for research or surveillance B. pertussis testing after getting approval from CDC.

Specimen, documentation, packaging, and shipping

Specimen requirements vary by the specific test requested.

The following provides information on specimen, documentation, packaging, and shipping requirements: B. pertussis and related species detection and identification

Resources

• Pertussis Outbreaks
• CDC's Pertussis and Diphtheria Laboratory
• CDC Surveillance Manual's Chapter on Pertussis – Laboratory Testing
• Antibiotic-resistant Bordetella pertussis

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