An enzyme-linked immunosorbent assay was developed for detection of immunoglobulin A (IgA) antibody to Bordetella pertussis (PsIgA) in nasopharyngeal secretions as an indicator of recent infection. Secretion specimens submitted for pertussis culture were examined for PsIgA by this technique. Of 348 specimens tested, B. pertussis was cultured from 57, and PsIgA was detected in 8 culture-positive and 40 culture-negative specimens. The average time between onset of symptoms and specimen collection for the culture-positive, PsIgA-negative specimens was 10 days; for the culture-positive, PsIgA-positive specimens, 15 days; and for the culture-negative, PsIgA-positive specimens, 36 days. Examination of paired samples available from several culture-proven cases demonstrated conversion from a negative PsIgA in the early sample to a positive PsIgA in the follow-up sample. Our results indicate that PsIgA is produced during natural human infection and does not arise as a result of parenteral vaccination. PsIgA usually appears in the nasopharyngeal secretions during the second or third week of illness and persists for at least 3 months. The detection of PsIgA in secretions may be a valuable diagnostic aid in culture-negative patients with pertussis
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