Article in Japanese

A 4-year-old child with a pertussis diagnosis initially based on a positive anti-Bordetella pertussis immunoglobulin M test result that was later suspected to be a false positive

Naoto NISHIMURA^1）, Naoko NISHIMURA^1）, Mai UMEHARA^1）, Takuya AKANO^1）, Takuma ANDO^1）, Kensei GOTOH^1）, Koji TAKEMOTO^1）, Takao OZAKI^1）

Definitive diagnosis of pertussis should be based on laboratory tests rather than clinical symptoms. A 4-year-old girl who had received four DPT-IPV vaccinations presented at our hospital with a cough that had developed 9 days previously. On day 9 (day of visit), isolation and DNA detection tests for Bordetella pertussis were negative, as were tests for anti-pertussis toxin (PT)-IgG antibody and anti-Bordetella pertussis IgA antibody. However, the test for anti-Bordetella pertussis IgM antibody was positive (13.9 NTU), leading to a diagnosis of pertussis. Six months later, the patient presented at our hospital again with a severe cough; Bordetella pertussis DNA was detected by nasal swab on day 4, and pertussis was diagnosed. The antibody test results on days 4 and 20 were anti-PT-IgG antibody, 11 (＋) and 140 (＋) EU/mL; anti-Bordetella pertussis IgM antibody, 11.0 (±) and 15.9 (＋) NTU; and anti-Bordetella pertussis IgA antibody, 1.8 (−) and 7.7 (−) NTU. Thus, anti-PT-IgG antibodies increased significantly, and anti-Bordetella pertussis IgM antibody changed to positive. Analysis results met the laboratory diagnostic criteria for antibody tests when paired serum samples from days 4 and 20 were used, but not when serum from day 4 only was used. The previous diagnosis of pertussis was suggested to be incorrect, based on the positive anti-Bordetella pertussis IgM antibody test from a single serum sample that may have been a false positive. This case highlights the importance of choosing the test and interpreting the test results for a definitive diagnosis of pertussis.

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1）Department of Pediatrics, Konan Kosei Hospital

Key words	pertussis, anti-Bordetella pertussis IgM antibody, anti-PT-IgG antibody, pathogen test, antibody test
Received	December 15, 2023
Accepted	April 15, 2024

36 (2)：159─164,2024