Testing for Whooping Cough: Culture, PCR or Serology — and When Each Works

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Which test finds whooping cough (pertussis) depends on when it is done. Clinical laboratories use three methods to identify Bordetella pertussis, and each has its window after the cough begins.

A CDC laboratorian setting up a PCR test sample for pertussis

A CDC laboratorian sets up a PCR test for pertussis. CDC.

The three tests

Method	Strengths	Weaknesses	Best time after cough onset
Culture	The gold standard; the only 100% specific method; more specific than PCR	Results take up to 7 days; less sensitive than PCR	First 2 weeks, while live bacteria are present; after that, false negatives become more likely
PCR	The fastest test; excellent sensitivity; assays with several target sequences can tell Bordetella species apart	Specificity varies between tests; high sensitivity raises the risk of false positives, though best practices reduce it	Up to 3–4 weeks; after the fourth week, bacterial DNA in the nose and throat falls off fast
Serology	Works much later in the illness than the other two	Some commercial tests have unproven or unknown accuracy	2–8 weeks, when antibody levels peak; possible up to 12 weeks, but less reliable

Chart of the optimal timing, in weeks after cough onset, for culture, PCR and serology

Optimal timing for each test, in weeks after the cough begins. CDC.

Read PCR results together with symptoms and the epidemiological picture. In an outbreak, at least one case should be confirmed by culture.

Serology: a CDC test, and a warning

CDC and the FDA developed a serologic assay that has helped confirm diagnoses, especially in suspected outbreaks; a few state public health laboratories use it, and it is available through CDC's test directory for research or surveillance. When CDC evaluated several commercial serologic tests used in the United States, it found wide variation, depending on the antigen or antibody measured and whether the test was calibrated to an international reference serum. The most promising measured IgG antibodies against pertussis toxin only, calibrated to a reference standard.

Taking the specimen

Providers should take a nasopharyngeal (NP) swab or aspirate — from the back of the nose — from everyone with suspected pertussis. The same specimen can be used for both culture and PCR, but technique matters for a good result. For culture, plate the specimen directly or put it straight into transport medium, and plate within 24 hours of collection.

Illustration and photograph of the technique for taking a nasopharyngeal specimen

Taking a nasopharyngeal specimen for Bordetella pertussis. From CDC's Manual for the Surveillance of Vaccine-Preventable Diseases, 2015.

Public health laboratories and other federal agencies can submit specimens to CDC for research or surveillance testing after CDC approval; requirements for specimens, paperwork, packaging and shipping vary by test.