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Case Report
Unexpected non-reactive nontreponemal serology in secondary syphilis: The prozone phenomenon and clinician–laboratory communication
Southern African Journal of Infectious Diseases | Vol 41, No 1 | a800 |
DOI: https://doi.org/10.4102/sajid.v41i1.800
| © 2026 Mahomed A. Aboo, Matilda Mphahlele, Melanie Louw, Nicholas Aikman
| This work is licensed under CC Attribution 4.0
Submitted: 15 November 2025 | Published: 24 April 2026
Submitted: 15 November 2025 | Published: 24 April 2026
About the author(s)
Mahomed A. Aboo, Department of Internal Medicine, Tambo Memorial Hospital, Johannesburg, South AfricaMatilda Mphahlele, Department of Dermatology, Tambo Memorial Hospital, Johannesburg, South Africa
Melanie Louw, Department of Anatomical Pathology, Charlotte Maxeke Johannesburg Academic Hospital, National Health Laboratory Service, Johannesburg, South Africa; and Department of Anatomical Pathology, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
Nicholas Aikman, Department of Anatomical Pathology, Charlotte Maxeke Johannesburg Academic Hospital, National Health Laboratory Service, Johannesburg, South Africa; and Department of Anatomical Pathology, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
Abstract
We describe a case of a 22-year-old woman living with human immunodeficiency virus (HIV) who presented with classical features of secondary syphilis. Initial Rapid Plasma Reagin (RPR) testing was unexpectedly non-reactive; however, repeat RPR testing with serum dilution yielded a reactive result, illustrating the prozone phenomenon.
Contribution: The prozone phenomenon is uncommon. We aim to encourage clinician–laboratory communication when there is a high pretest probability of syphilis, with serological discordance, to facilitate prompt diagnosis and treatment.
Keywords
secondary syphilis; prozone phenomenon; syphilis serology; serological discordance; Treponema pallidum
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