Specifically, the pertussis vaccines in current use (DTaP and Tdap) also contain other antigens (i

Specifically, the pertussis vaccines in current use (DTaP and Tdap) also contain other antigens (i.e., pertactin and fimbriae), and antibodies to these antigens are more likely to be serologic correlates of protection (4, 24). spanning 11 to 60 years of age but lower in the <11- and >60-year-old groups. In 3 of 5 age categories, a significant rise in the proportion of positive serum samples exhibiting increased FHA antibodies only occurred in 2010 2010. Patterns of positive antibody results varied with age. The predominance of increased FHA antibodies only in patients >20 years old suggests that many adults thought to have infections actually have other infections that induce FHA-reactive antibodies. Similarly, the 2010 rise in the frequency of increased FHA antibodies only in some age groups suggests an increase in non-infections. INTRODUCTION Cough illness (pertussis) due to contamination with remains a persistent CZC24832 problem in the United States, with epidemic cycles every 2 to 5 years (2, 3, 14). Many cases are not diagnosed because the disease is usually often not considered, particularly among adolescents and adults, and confirmation of the diagnosis poses challenges. Culture using special media is usually highly specific, but cultures are often unfavorable by the third week of illness, when the diagnosis may first be considered (1). PCR is being increasingly used for diagnosis and is more sensitive than culture, but sensitivity declines over time (1, 5). Measurement of antibodies can play an important role in the diagnosis of pertussis illness (1, 6C8, 13C17, 20, 22C26, 28), particularly after the second week of illness. Detection of an increased level of IgG or IgA antibody to pertussis toxin (PT) in a patient with prolonged cough illness provides strong support for a diagnosis of recent contamination. CZC24832 An increased level of IgG or IgA antibody to filamentous hemagglutinin (FHA) also occurs in contamination but is usually a less specific marker CZC24832 of contamination because other species express FHA and cross-reacting antibodies are also induced by other bacteria (14, 17, 26). The interpretation of increased antibody positive result patterns can be a challenge due to a variety of factors, including differing assay sensitivities and specificities and the complex relationship between patient age and the antibody isotypes produced following vaccination (25). Serum samples submitted to the Focus Diagnostics reference laboratory for the antibody panel (PT IgG, PT IgA, FHA IgG, FHA IgA) arrive from all geographic areas of the United States but are HDAC5 not accompanied by information indicating the reason for testing. The panel was originally developed for the serologic diagnosis of pertussis, and conversations with physicians indicate that, in most situations, it is used for this purpose. However, the panel is usually, on occasion, used by clinicians to assess the response to pertussis vaccination in children or to determine immunity or susceptibility to contamination. The panel’s use for the latter two reasons is usually problematic. Specifically, the pertussis vaccines in current use (DTaP and Tdap) also contain other antigens (i.e., pertactin and fimbriae), and antibodies to these antigens are more likely to be serologic correlates of protection (4, 24). As part of our overall goal of providing the most accurate panel interpretations possible for patients of all ages, we sought to characterize the frequencies at which various positive (increased) antibody detection patterns occur and assess the relationship of a given pattern to patient age. MATERIALS AND METHODS Serum samples submitted to Focus Diagnostics for pertussis antibody testing were evaluated using a validated tetraplex microsphere-based multianalyte immunodetection assay as previously described (21); the four analytes measured were PT IgG, PT IgA, FHA IgG, and FHA IgA. Results were expressed quantitatively as IU/ml based on interpolation from a secondary standard with assigned values traceable to the World Health Organization international antibody standard (29). Reference ranges, based on the 95th percentile values obtained for a group of 200 blood donor serum samples collected in 2005, were as follows: PT IgG, <45 IU/ml; PT IgA, <10 IU/ml; FHA IgG, <90 IU/ml; FHA IgA, <50 IU/ml. Values within the reference range for a given analyte were considered normal, whereas values above the reference range were considered increased (positive). Differences among proportions were evaluated by chi-square analysis (MedCalc Software, Mariakerke, Belgium). values were corrected.