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Pertussis Test 

  • Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Eric B Staros, MD  more...
 
Updated: Jan 17, 2014
 

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Pertussis is a respiratory tract infection caused by the gram-negative coccobacillus Bordetella pertussis. Pertussis is transmitted by droplet transfer (usually from sneezing or coughing) from an infected person. Pertussis is also known as whooping cough.

In most cases, a negative pertussis result indicates the absence of whooping cough.

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Interpretation

A positive result indicates the presence of whooping cough.

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Collection and Panels

The specimen collected is nasopharyngeal secretions or blood.

Nasopharyngeal secretions (aspirate or swab)

Place the nasopharyngeal swab into a transport medium or plate it directly immediately. The aspirates should be dispensed and plated within 24 hours of collection. Plate the specimens onto a special charcoal blood agar medium to which a cephalosporin has been added to aide selectivity. Throat swabs are not suitable because the cilia to which the organism attach are not present in the throat.[1]

Either polymerase chain reaction (PCR) or culture can be performed on the same specimen. For best results with PCR testing, the specimen should be collected within the first 5 weeks of illness. If the specimen is obtained within 4 weeks in infants or nonvaccinated individuals, it can still yield accurate results. Culture takes longer (up to 1 wk), but its specificity is better.[2]

Blood for serological tests

The container used for blood collection is a Serum Separator Tube (SST) for serological tests.

To comply with Occupational Safety and Health Administration (OSHA) safety standards, all samples must be sent in a sealed, leak-proof container marked with a biohazard sticker.

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Background

Description

Pertussis is a respiratory tract infection caused by the gram-negative coccobacillus B pertussis. Pertussis is transmitted by droplet transfer (usually from sneezing or coughing) from an infected person. Pertussis is also known as whooping cough.

Despite the fact that pertussis can be prevented through vaccination, its incidence has increased in recent years, owing to a decline in immunity from previous vaccinations and a decrease in the vaccination rate.[3] Recent estimates put the worldwide incidence of pertussis at 48.5 million cases, with close to 295,000 deaths per year.[4] Among infants, the case-fatality rate is estimated to be as high as 4% in low-income countries.[4]

The newer acellular pertussis vaccine (DTaP), which is approved for adults, has a significantly better adverse effect profile compared with the older DPT vaccine, which should help increase vaccination rates. World Health Organization (WHO) estimates suggest that in 2008, approximately 82% of all infants worldwide received 3 doses of pertussis vaccine, which prevented approximately 687,000 deaths.[5]

Whooping cough primarily affects infants younger than 2 years. In fact, half the cases worldwide occur in infants younger than 2 years. Adults and adolescents are important reservoirs of infection because neither infection nor immunization results in lasting immunity.

Pertussis has the following 3 stages:

  • Catarrhal (prodromal stage of malaise, coryza, and cough)
  • Paroxysmal (cough ending in a high-pitched inspiratory “whoop” sound, hence the name whooping cough)
  • Convalescent stage

With the addition of adenosine diphosphate-ribose onto the inhibitory G protein, adenylate cyclase is stimulated by the pertussis toxin, which has 2 components: subunit A and subunit B. Subunit A has the adenosine diphosphate-ribosylating activity. Subunit B binds the toxin to the cell surface receptors, thereby inhibiting chemokine receptors, with the result being lymphocytosis. Ciliated epithelium in the respiratory tract is thus damaged by tracheal cytotoxin.[6]

Culture testing is the criterion standard for B pertussis infection, owing to its high specificity (100%) for identification.

For a more rapid diagnosis, direct immunofluorescent antibody (DFA) testing on nasopharyngeal smears may be an option. However, the sensitivity and specificity of DFA vary (owing to the quality of the reagents), and test results should be confirmed by culture, if at all possible.[1]

Serologic assays are useful in later stages of the disease and can be useful for diagnosis confirmation, particularly if a pertussis outbreak is suspected. The specific type of serological test varies from laboratory to laboratory. While accurate serology results can be achieved on specimens collected up to 3 months after cough onset, testing for a single-point serology is more accurate if the specimen is collected 2-8 weeks after cough onset.

PCR testing can be used for confirmation and to identify the distinct Bordetella species. However, with the variable specificity of PCR results, the scenario of a pertussis outbreak dictates that pertussis be confirmed by culture testing on at least one suspicious case. PCR testing of nasopharyngeal specimens is optimally performed up to 3 weeks after cough onset. The risk of false-negative results is increased if the specimen is collected 4 weeks after cough onset, owing to a rapid decrease in the amount of bacterial DNA.

Indications/Applications

Pertussis testing is indicated for suspected cases of whooping cough.

Considerations

Clinical symptoms of pertussis are similar to those of other infections, such as croup or bronchiolitis from respiratory syncytial virus (RSV) in children, viral or bacterial pneumonia, and other causes of chronic cough in adults (eg, postnasal drip, gastroesophageal reflux disease, asthma, tuberculosis); therefore, isolation of the bacterium and confirmation of the pertussis diagnosis if very important, particularly if an outbreak is suspected. The best time frame for nasopharyngeal specimen collection for culture testing is within the first 2 weeks of cough onset, when viable bacteria are present.

The US Centers for Disease Control and Prevention (CDC) provides laboratory support to US public health departments that request assistance with isolation, identification, and subtyping various bacterium, including B pertussis, Bordetella parapertussis, Bordetella holmesii, Bordetella bronchiseptica, Corynebacterium diphtheriae, and Corynebacterium ulcerans. The CDC’s laboratory is available for resources and outbreak support to domestic state and local health departments, domestic and international researchers, and other laboratory and hospital personnel.[2]

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Contributor Information and Disclosures
Author

Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP Associate Professor of Medicine, St Louis University School of Medicine

Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP is a member of the following medical societies: American College of Physicians, American Medical Informatics Association, Royal College of Physicians and Surgeons of Glasgow, Royal College of Surgeons of Edinburgh, Healthcare Information and Management Systems Society

Disclosure: Nothing to disclose.

Chief Editor

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

References
  1. Ryan K, Ray CG, Ahmad N, Drew WL, Plorde J. Haemophilus and Bordetella. Sherris Medical Microbiology. 5th ed. New York, NY: McGraw-Hill; 2010.

  2. Centers for Disease Control and Prevention. Specimen Collection. Pertussis. Available at http://www.cdc.gov/pertussis/clinical/diagnostic-testing/specimen-collection.html. Accessed: April 27, 2012.

  3. Williamson MA, Snyder LM. Wallach's Interpretation of Diagnostic Tests (Interpretation of Diagnostric Tests). Philadelphia, Pa: Williams & Wilkins; 2011. 9th ed:

  4. Bettiol S, Thompson MJ, Roberts NW, Perera R, Heneghan CJ, Harnden A. Symptomatic treatment of the cough in whooping cough. Cochrane Database Syst Rev. 2010 Jan 20. CD003257. [Medline].

  5. World Health Organization. Pertussis. Immunization, Vaccines and Biologicals. Available at http://www.who.int/immunization/topics/pertussis/en/index.html. Accessed: April 27, 2012.

  6. Levinson W. Brief Summaries of Medically Important Organisms. Review of Medical Microbiology and Immunology. 2010. New York, NY: McGraw-Hill; 11th ed:

 
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