Bordetella pertussis Antibodies, IgM

The Bordetella pertussis Antibodies, IgM assay (also referred to as Anti-Bordetella pertussis IgM or Pertussis IgM antibodies) assists in the serologic diagnosis of pertussis by identifying pathogen-specific IgM. It supports recognition of acute or ongoing infection beginning about the second week after symptoms start and has particular utility in unvaccinated children. This test is interpreted alongside clinical and epidemiologic information and is commonly paired with direct detection methods such as culture and PCR to confirm infection.

Pertussis is a human respiratory illness caused by the aerobic, gram-negative coccobacillus Bordetella pertussis and spreads via respiratory droplets. The illness follows incubation, catarrhal, paroxysmal, and convalescent stages; the paroxysmal phase features spasmodic coughing, an inspiratory whoop, and vomiting after coughing. Leukocytosis with absolute lymphocytosis is frequently observed. Major antigens that elicit host antibody responses include pertussis toxin, filamentous hemagglutinin, pertactin, outer-membrane proteins, lipopolysaccharide, and agglutinogens. Humoral responses evolve over time: IgA and IgM usually emerge during the second week after symptom onset, while IgG reaches a peak around weeks 6–8 and then wanes. Finding elevated Bordetella pertussis–specific IgM, either alone or together with IgA and/or IgG, supports an acute or recent infection, particularly in persons without prior vaccination. Very early sampling or altered immune function may result in low IgM despite true infection. Serology serves as an adjunct to culture and PCR, and results require interpretation in the context of the clinical presentation and epidemiologic exposure.