Specificity and Sensitivity of High Levels of Immunoglobulin G Antibodies against Pertussis Toxin in a Single Serum Sample for Diagnosis of Infection with Bordetella pertussis

Abstract

Laboratory confirmation of pertussis by culture, PCR, or detection of antibody increase in paired sera is hampered by low sensitivity in the later stages of the disease. Therefore, we investigated whether, and at which level, concentrations of immunoglobulin G (IgG) antibodies against pertussis toxin (PT), IgG-PT, in a single serum sample are indicative of active or recent pertussis. IgG-PT, measured by enzyme-linked immunosorbent assay in units per milliliter, was analyzed in 7,756 sera collected in a population-based study in The Netherlands, in the sera of 3,491 patients with at least a fourfold increase of IgG-PT, in paired sera of 89 patients with positive cultures and/or PCR results, and in the sera of 57 patients with clinically documented pertussis with a median follow-up of 1.4 years. We conclude that, independently of age, IgG-PT levels of at least 100 U/ml are diagnostic of recent or active infection with Bordetella pertussis. Such levels are present in less than 1% of the population and are reached in most pertussis patients within 4 weeks after disease onset and persist only temporarily.

International Bordetella pertussis assay standardization and harmonization meeting report. Centers for Disease Control and Prevention, Atlanta, Georgia, United States, 19–20 July 2007

“…Another study was done without age limit in a mostly vaccinated population (Netherlands) using a cutoff of ∼125 EU/ml (99th percentile of population). The study found a sensitivity of 76.4%, whereas a cutoff ∼62 EU/ml (∼95th percentile of population) had a sensitivity of 88.8% [61].…”

“…The cutoff point was set at 20 g/ml, which is equivalent to 200 CBER units per ml. This is actually quite high relative to what other groups have chosen [58,61].…”

“…The WHO collaborative study, "Evaluation of proposed international reference preparations for pertussis antiserum (human),"was a multicenter collaboration between NIBSC, UK; the Center for Biologics Evaluation and Research (CBER) at the Food and Drug Administration (FDA), US; the Institut für Infektiologie (IFI), Germany; and a number of international participants. Reference sera from the United States (US reference pertussis antiserum [human] lot 3 and lot 4 for IgG-antibodies and lot 5 for IgA-antibodies) were prepared by FDA, CBER more than 10 years ago, and since then have been commonly used as reference standards for pertussis serologic assays [58][59][60][61][62][63]. Currently, only limited quantities of these sera remain.…”

“…Because of the difficulty with standardization of cell extracts, the ESEN project emphasized purified antigens, focusing on IgG anti-PT assays because of the higher sensitivity and specificity for serodiagnosis [62]. Since most individuals had been exposed to pertussis vaccine or infection, the study focused on an estimation of the incidence of recent infections, as defined by the presence of IgG anti-PT antibodies above defined thresholds [61]. To accomplish this, quantitative assays were required and standardization efforts were based on analytical performance in the assay range near the diagnostic thresholds.…”

Aetiology of lower respiratory tract infection in adults in primary care: a prospective study in 11 European countries

“…A patient was considered positive for an acute B. pertussis infection (infection in the last 6 months) if positive by PCR in a respiratory sample and/or the presence of an antibody titre to pertussis toxin of !125 IU/mL in convalescent serum (days 28e35), demonstrated previously as a cut-off with high sensitivity and specificity [8,9].…”