Pertussis tests are used to detect and diagnose a Bordetella pertussis infection. Early diagnosis and treatment may lessen the severity of symptoms and help limit spread of the disease.
There are several tests that may be used when a pertussis infection is suspected:
- Culture – this test has been the “gold standard” for identifying pertussis and is used to diagnose a pertussis infection. The sample is put into nutrient media and the bacteria are grown and identified. Results are reported in one to two weeks.
- Polymerase Chain Reaction (PCR) – this test amplifies the genetic material of the bacteria in a sample and is available within a couple of days.
- Direct Fluorescent Antibody (DFA) – this test is not as widely used as it once was. It is less specific and sensitive than the pertussis culture and PCR.
- Antibodies, IgA, IgG, IgM – these blood tests measure the body’s immune response to a pertussis infection.
Other tests that may occasionally be ordered include:
- Toxin antibodies, IgA, IgG – these blood tests measure the body’s immune response to toxins released by B. pertussis.
- B. pertussis molecular sub-typing – this test may be ordered not to benefit an individual patient, but so that health professionals can better understand the strain and severity of the B. pertussis present in a community during an outbreak.
Typically a pertussis culture and PCR test will both be ordered, as early in the illness as possible. Cultures are less likely to grow the organism 2-3 weeks into the illness, and cultures will be affected by some antimicrobial agents if the patient has been treated.
Since the introduction of PCR testing, the use of direct fluorescent antibody testing has significantly decreased. When used, it should be ordered along with a pertussis culture to recover the organism in order to investigate potential outbreaks and perform antimicrobial susceptibility testing.
Pertussis antibody testing is not used frequently. Acute and convalescent samples, collected several weeks apart, are sometimes ordered on a person who has not sought treatment until late in their illness or on an adult who has had a cough for an extended period of time. They are ordered to help determine if the person has had a recent pertussis infection. Pertussis IgG antibodies will be present in anyone who has been vaccinated. Pertussis IgM and IgA antibodies will usually only be present a short time after vaccination or infection. These tests may sometimes be ordered to help evaluate and study the spread of pertussis in the community. Rarely, an antibody test may be performed to evaluate the adequacy of a person’s immune response to a pertussis vaccine.