Early positivity of IgG preceding IgM is a common serological pattern in secondary dengue infections, leading to potential diagnostic errors if not recognized.
Recognizing the serological pattern of early IgG positivity before IgM is crucial for accurately diagnosing secondary dengue infections and avoiding misinterpretation.
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Dengue is an arbovirus disease with high prevalence in Brazil, requiring accurate diagnosis for proper management and epidemiological surveillance. In primary infections, serological positivity follows the NS1, IgM, and later IgG pattern. In secondary infections, however, IgG can become positive early, preceding IgM, which can generate misinterpretations when disconnected from clinical and epidemiological data. This work presents a case series illustrating the importance of recognizing this serological pattern in secondary dengue. Four suspected dengue cases were evaluated between September 2024 and April 2025 in a reference service, followed with serial serologies (NS1, IgM, IgG), complete blood count, clinical data, and prior dengue history. Case 1: female patient, 34 years old, on the 5th day of symptoms, with IgG positive and IgM seroconversion the next day. Case 2: female patient, 84 years old, initially with negative serologies, evolving to IgG positive on the 8th day and IgM positive later. Case 3: female patient, 31 years old, with initially negative serologies, IgG positive on the 4th day of symptoms and IgM positive on the 6th day. Case 4: male patient, 56 years old, presented hemoconcentration, significant thrombocytopenia (21 thousand), elevated liver enzymes, IgG positive on the 3rd day and IgM positive on the 4th day, with subsequent platelet recovery. All cases had history compatible with prior dengue and typical clinical signs, and were followed without severe complications. The serological pattern of early IgG positivity before IgM is characteristic of secondary dengue infections, but still poorly recognized in practice, and can lead to diagnostic errors. It is essential to associate serological interpretation with the clinical picture, warning signs, prior dengue history, local epidemiology, and complete blood count, ensuring proper diagnosis and management during outbreaks, avoiding underdiagnosis and failures in follow-up.
Leandro César da Silva (Sun,) reported a other. Early positivity of IgG preceding IgM is a common serological pattern in secondary dengue infections, leading to potential diagnostic errors if not recognized.