Pertussis diagnostics: overview and impact of immunization

Abstract

In all vaccinated populations, infections with Bordetella pertussis and Bordetella parapertussis continue to cause infections in unvaccinated infants and children, as well as in adolescents and adults with waning immunity. Thus in patients with longer lasting coughs a diagnosis of pertussis should be entertained irrespective of their vaccination status. Due to the non-specific clinical symptoms, clinically suspected cases of pertussis must be verified by laboratory methods. Hyperleukocytosis may be helpful in diagnosis for young infants, but in most cases, nonspecific laboratory tests have no role in pertussis diagnosis. Specific laboratory tests include direct detection of the bacteria or their DNA by culture or PCR, whereas serology serves as an indirect method to diagnose pertussis in those patients who present late in the development of the disease. Serology results can be interpreted in relation to reference values for different populations, but serology is unable to distinguish between vaccination and infection.

Keywords::

• Bordetella pertussis
• culture
• ELISA
• parapertussis
• PCR
• serology

Financial & competing interests disclosure

CH Wirsing von Konig is a member of the‘Global Pertussis Initiative’, which is sponsored by Sanofi Pasteur; he is also on the Speakers bureau of GlaxoSmithKline Biologicals SA. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Bordetella pertussis and Bordetella parapertussis cause pertussis or whooping cough, which is a vaccine-preventable disease in childhood.

• Neither natural infection nor vaccination with whole-cell or acellular (ap) vaccines induces a life-long immunity. Consequently, reinfections are common.

• In countries with high vaccine coverage, the disease mainly occurs in unvaccinated infants, older children adolescents and adults. Infants are often infected by their parents or other adults.

• The ‘typical’ symptoms of pertussis such as whooping or paroxysmal coughing occur less often in re-infections. In adolescents and adults, the disease often presents as long-lasting non-productive cough without fever that worsens at night.

• Hyperleukocytosis can be a helpful diagnostic criterion in young infants. In other patients, non-specific laboratory tests are of little value.

• The infection can be diagnosed by detecting the bacteria by culture or by detecting Bordetella-DNA by PCR. PCR is the method of choice because it is faster and more sensitive.

• The quality of nasopharyngeal aspirate or nasopharyngeal swabs is critical for the sensitivity of direct detection methods.

• Measuring antibodies to pertussis toxin by ELISA or bead-based immunoassays is a valid method for indirect diagnosis of pertussis; however, it is not suitable for parapertussis. Antibodies should be quantified and reported in international units, and either an increase in antibody concentration or a single high concentration signifies a recent contact.

• Antibodies are induced by natural infection or by vaccination with ap vaccivnes, so for 1 year after ap vaccination, pertussis serology is difficult to interpret.

Notes