The Test Sample
What is being tested?
Bordetella pertussis is a bacterium that targets the lungs, typically causing a three-stage respiratory infection that is known as pertussis or whooping cough. It is highly contagious and causes a prolonged infection that is passed from person to person through respiratory droplets and close contact. Pertussis tests are performed to detect and diagnose a B. pertussis infection.
The incubation period for pertussis varies from a few days to up to three weeks. The first stage of the disease, called the catarrhal stage, usually lasts about two weeks and symptoms may resemble a mild cold. It is followed by the paroxysmal stage, which may last for one or two weeks or persist for a couple of months and is characterized by severe bouts of coughing. Eventually, the frequency of the coughing starts to decrease and the infected person enters the convalescent stage, with coughing decreasing over the next several weeks. Pertussis infection, however, can sometimes lead to complications such as encephalitis and seizures and it can be deadly. Infants tend to be the most severely affected and may require hospitalization.
Pertussis infections used to be very common in the United States, affecting about 200,000 people in epidemics that would occur every few years. Since the introduction of a pertussis vaccine and widespread vaccination of infants, this number has drastically decreased. However, since neither the vaccine nor the pertussis infection confers lifetime immunity, health professionals are still seeing periodic outbreaks of pertussis in young, unvaccinated infants, in adolescents, and in adults. According to the Centers for Disease Control and Prevention (CDC), there were over 27,000 cases of whooping cough reported in 2010, and many more that went unreported. In 2011, the Advisory Committee on Immunization Practices updated their recommendations for pertussis booster shots.
- For children and teens ages 11 through 18 years old, a single booster shot is advised for those who have completed the recommended childhood diphtheria, tetanus and pertussis (DTP/DTaP) series of vaccinations.
- For adults aged 19 through 64 years, a one-time vaccination is recommended.
- Adults 65 years and older who are or expect to be in close contact with infants, such as grandparents and child- and health-care providers, should receive a dose to boost their immunity if they had not previously done so.
Pertussis testing is used to diagnose these infections and to help minimize their spread to others. Several different types of tests are available to detect pertussis infection. Some of these include:
- Detection of pertussis genetic material (Polymerase Chain Reaction, PCR)
- Direct fluorescent antibody (DFA)
- Blood tests for pertussis antibodies (serology), IgA, IgG, IgM
Pertussis can be challenging to diagnose at times because the symptoms that present during the catarrhal stage are frequently indistinguishable from those of a common cold or of another respiratory illness such as bronchitis, influenza (flu), and, in children, respiratory syncytial virus (RSV). In the paroxysmal stage, many adults and vaccinated people who have pertussis will present with only persistent coughing. Suspicion of pertussis infection is increased in people who have the classic "whoop," in people who have cold symptoms and have been in close contact with someone who has been diagnosed with pertussis, and when there is a known pertussis outbreak in the community. A pertussis culture and/or PCR test will usually be ordered on these people but should not be performed on close contacts who do not have symptoms.
How is the sample collected for testing?
Sample collection technique is critical in pertussis testing. For a culture or for a test for genetic material (PCR) or for DFA, a nasopharyngeal (NP) swab or nasal aspirate is used. The nasopharyngeal swab is collected by having you tip your head back and then a Dacron swab (like a long Q-tip with a small head) is gently inserted into one of your nostrils until resistance is met. It is left in place for several seconds, then rotated several times to collect cells, and withdrawn. This is not painful, but it may tickle a bit, cause your eyes to tear, and provoke a coughing paroxysm. For a nasal aspirate, a syringe is used to push a small amount of sterile saline into your nose, and then gentle suction is applied to collect the resulting fluid. For antibody testing, a blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.