A Bordetella pertussis IgG antibody test is a common laboratory procedure. Receiving a “high” result can lead to confusion about what this means for one’s health. This article aims to clarify the implications of a high Bordetella pertussis IgG antibody level, providing a comprehensive understanding of this specific test result.
Understanding Pertussis and Antibody Tests
Pertussis, also known as whooping cough, is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis. It is characterized by severe coughing fits, which can be particularly dangerous for infants, sometimes leading to hospitalization or other serious complications.
The body’s immune system responds to infections or vaccinations by producing antibodies, proteins that identify and neutralize specific pathogens. Immunoglobulin G (IgG) antibodies represent a type of long-term immune memory. These antibodies persist in the bloodstream for an extended period after an infection or vaccination, indicating past exposure or immunity.
The Bordetella pertussis IgG antibody test measures these specific IgG antibodies in a blood sample. This test primarily targets antibodies against pertussis toxin (PT), a substance produced exclusively by Bordetella pertussis.
Deciphering High IgG Antibody Levels
A high Bordetella pertussis IgG antibody level indicates either a recent or past exposure to the bacterium or a response to vaccination. Levels of 100 IU/mL or greater are considered positive, suggesting a recent infection or vaccination.
A high IgG level can mean a recent infection occurred weeks to months prior. These levels may stay elevated for several years, gradually declining over time.
A high IgG level can also signify a successful immune response following pertussis vaccination, such as with DTaP or Tdap vaccines. These vaccines contain components of the Bordetella pertussis bacterium, including pertussis toxin, which stimulate the production of protective antibodies. The immune response from vaccination cannot be distinguished from that of a recent infection using this test alone.
A single high IgG antibody result, without additional context, does not definitively confirm a current, active pertussis infection. The test primarily reflects past exposure or vaccination. Therefore, a healthcare provider will consider a patient’s symptoms, age, and vaccination history when interpreting the results.
Confirming a Pertussis Diagnosis
Since a high IgG antibody level does not confirm an active infection, a diagnosis of current pertussis involves other methods. Healthcare providers first consider characteristic clinical symptoms, which include a cough lasting two or more weeks, accompanied by paroxysmal coughing, an inspiratory “whoop,” or post-tussive vomiting.
To confirm an active infection, other diagnostic tests are used. Polymerase Chain Reaction (PCR) testing is a sensitive and rapid method that detects the bacterium’s genetic material from a nasopharyngeal swab. PCR is most effective when performed within the first three to four weeks of cough onset, as the bacterial DNA diminishes rapidly afterward.
Bacterial culture, while specific and considered the “gold standard” for diagnosis, involves growing the bacteria from a swab. This method can take up to seven days for results and is most sensitive during the first two weeks of illness, decreasing in sensitivity later in the disease course. Another approach for diagnosing recent infection, particularly after two weeks of symptoms, involves acute and convalescent serology, where a significant rise in IgG levels between two blood samples taken weeks apart indicates a recent infection.
Management and Prevention
If a pertussis diagnosis is confirmed, treatment involves antibiotics, especially if administered early in the course of the illness. Early antibiotic treatment, within the first one to two weeks of symptoms, can help reduce the severity and duration of the illness and prevent further spread of the bacteria. Common antibiotics used include azithromycin, clarithromycin, and erythromycin.
To prevent transmission, individuals with pertussis should practice good hygiene, such as covering coughs and sneezes, and staying home when sick. Antibiotic prophylaxis may be recommended for close contacts, particularly those at high risk for severe illness like infants, immunocompromised individuals, or pregnant women.
Vaccination remains the most effective strategy for preventing pertussis. The DTaP vaccine is administered to children, while the Tdap booster is recommended for adolescents, adults, and pregnant women. Pregnant individuals should receive Tdap between 27 and 36 weeks of gestation with each pregnancy to transfer protective antibodies to the newborn. If you have a high Bordetella pertussis IgG result, consulting a healthcare provider is important to discuss the findings in the context of your symptoms and medical history.