At a Glance
To detect and diagnose a Bordetella pertussis infection, commonly known as whooping cough
When you have persistent spasms or fits of coughing (paroxysms) that the healthcare practitioner suspects is due to pertussis (whooping cough); when you have symptoms of a cold and have been exposed to someone with pertussis
A nasopharyngeal (NP) swab or a nasal aspirate; occasionally, a blood sample drawn from a vein in your arm
The Test Sample
Pertussis, commonly called whooping cough, is a respiratory infection caused by the bacteria Bordetella pertussis. These bacteria are highly contagious and are passed from person to person through respiratory droplets and close contact. Pertussis tests are performed to detect and diagnose a B. pertussis infection.
B. pertussis typically cause a prolonged, three-stage infection. The incubation period varies from a few days to up to three weeks.
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. (For details on the pertussis vaccine, see the Centers for Disease Control and Prevention (CDC)'s Pertussis: Summary of Vaccine Recommendations.)
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 CDC, there are 10,000 to 40,000 cases reported each year. Over 48,000 cases of whooping cough were reported in 2012, the most recent peak year, and many more went unreported.
Pertussis testing is used to diagnose these infections and to help minimize their spread to others. A few different types of tests are available to detect pertussis infection:
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).
Many adults and vaccinated people with pertussis will present with only persistent coughing and not the classic paroxysmal cough. 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. Testing should not be performed on close contacts who do not have symptoms.
Sample collection technique is critical in pertussis testing.
For a culture or for a test for genetic material (PCR), a nasopharyngeal (NP) swab or nasal aspirate is used. The nasopharyngeal swab is collected by having the patient tip their head back and then a Dacron swab (like a long Q-tip with a small head) is gently inserted into one of the 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 the person's eyes to tear, and provoke a coughing paroxysm.
For a nasal aspirate, a syringe is used to insert a small amount of sterile saline into the nasal passage 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.
No test preparation is needed.
Pertussis tests are used to detect and diagnose a Bordetella pertussis infection, commonly known as whooping cough, a highly contagious infection of the respiratory tract. Early diagnosis and treatment may lessen the severity of symptoms and help limit spread of the disease. (For more on the infection, see the "What is being tested?" section.)
There are a few test methods that may be used to detect a pertussis infection:
Pertussis tests are ordered when someone has signs and symptoms suggestive of pertussis, and as early in the illness as possible (generally within the first two weeks for culture and the first three weeks for PCR).
Symptoms during the first stage of the infection, called the catarrhal stage, may include typical cold symptoms such as a runny nose, sneezing, mild cough, and/or a low-grade fever. After about two weeks, the paroxysmal stage begins and may include symptoms such as:
These symptoms may last for one or two weeks or persist for a couple of months. During the convalescent stage, the severity of symptoms lessens, with the frequency of coughing gradually decreasing over the next several weeks.
A positive PCR test means that it is likely that the person has pertussis. However, the PCR test may also be positive with other Bordetella species. A negative PCR test means that it is less likely that the person has pertussis but does not rule it out. If there are an insufficient number of bacteria in the sample, then they may not be detected.
A positive culture is diagnostic for a B. pertussis infection, but a negative culture does not rule it out. Culture results are dependent on proper specimen collection and transport, duration of symptoms, when the sample is collected, and prior antimicrobial therapy administered before the culture is taken.
Both culture and PCR tests are less likely to be positive as the illness progresses.
The pertussis vaccination is given to infants as a series of shots. Those children who have not completed the series of pertussis vaccinations are at a higher risk of becoming infected. Even some people who have been vaccinated may be infected by Bordetella pertussis, but they will tend to have a less severe illness.
Pertussis is treated with antibiotics, which will help to resolve the infection and help stop spread of the disease.
International travelers should be aware that many less developed countries do not have widespread vaccination for pertussis. Infants who have not completed their series of vaccinations and people who have not had a booster vaccination in many years may be at an increased risk of contracting pertussis.
Pregnant women are advised to be re-vaccinated to prevent transmission of pertussis to the newborn. Grandparents and other caretakers who will be spending time with a newborn are also advised to be re-vaccinated.
Direct fluorescent antibody (DFA) is a test method that is no longer recommended to detect pertussis infections since it is less specific and sensitive than either the pertussis culture or PCR.