Pertussis

This is a group of tests that are performed to detect and diagnose a Bordetella pertussis infection. B. 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.

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 pneumonia, 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 two hundred thousand 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 to several thousand a year. 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.

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:

• Culture
• Detection of pertussis genetic material (Polymerase Chain Reaction, PCR)
• Direct fluorescent antibody (DFA)
• Blood tests for pertussis antibodies, 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, and, in children, Respiratory Syncytial Virus (RSV). In the paroxysmal stage, many adults and vaccinated patients who have pertussis will present with only persistent coughing. Suspicion of pertussis infection is increased in patients 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 patients but should not be performed on close contacts that do not have symptoms.

Sample collection technique is critical in pertussis testing. For a culture and/or a test for genetic material, 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.

No test preparation is needed.