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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 culturepositive 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 followup 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.

Nasopharyngeal culture, direct immunofluorescence, and serology of acute-phase and paired serum specimens were compared for the laboratory diagnosis of infections due to Bordetella pertussis in a community-based pediatric population with both high vaccine usage and high pertussis incidence. In 77 (37%) of 210 patients evaluated, one or more tests were positive for pertussis. A clinical illness compatible with pertussis was present in 52 (71%) of 73 pertussis test-positive and 42 (35%) of 119 test-negative patients (P < 0.001). Nasopharyngeal culture was of low sensitivity (20 [26%] of 77 positive tests) but was most commonly confirmed by another positive pertussis test (85%). Direct immunofluorescence was both insensitive and nonspecific; only 6 (30%) of 20 cases positive by culture were positive by immunofluorescence, and only 4 (33%) of 12 of the culture-negative, immunofluorescence-positive cases could be confirmed by another positive pertussis test. Although serology by enzyme immunoassay proved to be the most sensitive of the laboratory tests (87%), this sensitivity could be achieved only by assaying both acute-phase and paired serum specimens and measuring immunoglobulin G (IgG), IgA, and IgM antibodies to two pertussis antigens (pertussis toxin and filamentous hemagglutinin). Loss of sensitivity occurred with any reduction in the number of these serologic assays performed. Optimal laboratory diagnosis of endemic pertussis in a pediatric population requires both nasopharyngeal culture and serology by enzyme immunoassay.

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I N comparison with the vast literature concerning group-A streptococci, our knowledge of group-F streptococci is very meagre and there is little published work concerning them. This report documents a series of 22 strains isolated from children and puerperal women during about 4 years and discusses their significance in human disease. MATERIALS AND METHODSPrimary cultures were inoculated on horse-blood agar (BBL Columbia Base; Becton, Dickinson and Co., Canada, Ltd, Mississauga, Ontario) and incubated at 37°C under aerobic and anaerobic conditions for up to 48 h. Haemolytic colonies were examined microscopically and Gram-positive cocci were inoculated into Todd-Hewitt Broth (BBL). These cultures were incubated at 37°C overnight and used for preparing antigen by the method of Rantz and Randall (1955). Lancefield groups were determined by the microprecipitin technique (Lancefield, 1938) with grouping sera purchased from Burroughs Wellcome Ltd, Beckenham, Kent.Sensitivity to bacitracin (Maxted, 1953) was tested with standard bacitracin disks (BBL Tax0 A) and Columbia horse-blood agar. Some strains were inoculated on to aesculin-bileagar slopes (Difco Aesculin Bile Agar, Difco Laboratories, Detroit, USA) or aesculin-agar slopes. RESULTSDuring the period 1971-74 inclusive, some 3500 strains of haemolytic streptococci were subjected to Lancefield grouping. Of these, 22 strains isolated from 22 different patients belonged to Lancefield's group F. Eight of the strains were from peritoneal-cavity swabs taken at operation, in seven for acute appendicitis and in one for ruptured jejunum; five strains were from the vagina of puerperal women; two isolates were from urine, and one from the perineum of one of these patients was presumably related to the infection of the urine. One strain came from an abscess in the neck of a patient who had a history of dental infection, one from an ear swab from a child with cerebrospinal fluid (CSF) leaking from the ear, and one from a maxillary sinus.All group-F organisms were isolated from mixed cultures and since they were selected for further study because they were haemolytic on horse-blood agar, non-haemolytic strains would not have been recognised. Eight strains were quite fastidious anaerobes, two were microaerophilic, and 12 grew readily and were easily recognised on aerobic culture.Colonial morphology was variable. Nine of the strains grew very slowly, producing the classically described pinpoint colonies and attracting attention because of their haemolysis (Long and Bliss, 1934) but 13 strains produced colonies that were easily visible after overnight incubation. One strain was isolated repeatedly in pure culture from the urine and perineum of a patient who had undergone a renal transplant. Several strains, including this one, grew so slowly in Todd-Hewitt broth that incubation for 5-7 days was required before growth was adequate for the production of grouping antigen. All strains gave clear precipitin