Serological Response and Associated Prognostic Factors in Paracoccidioidomycosis: A 15-Year Retrospective Study.

Background: Small studies have used various serological methods to evaluate the response to paracoccidioidomycosis (PCM) treatment, with limited use of counterimmunoelectrophoresis (CIE). This study assessed CIE titres during and after PCM therapy and their prognostic value for serological negativity.

Methods: In this retrospective study, we reviewed medical records of patients with positive serology in proven or probable PCM from 2006 to 2021 at University of São Paulo. We performed multivariate logistic regression to identify independent variables associated with CIE titre negativity.

Results: This study included 144 participants, totalling 979 serology samples analysed, with a predominance of middle-aged adults (median age 50 years), males (n = 112, 78%) and chronic form (n = 112, 78%). Trimethoprim-sulfamethoxazole (n = 79, 55%) and itraconazole (n = 55, 38%) were the drugs most commonly used. The median treatment time was 24 months (IQR 16-37). Median initial CIE titre was 1:32 (IQR 1:16-1:128). Thirty-seven patients (26%) had a negative CIE titre, and 105 patients (73%) had CIE titres ≤ 1:4 at the last medical appointment. In multivariate analysis, only positive direct microscopy examination (OR 0.32, p = 0.043) was an independent factor related to non-negativity serology. The time to negativity was shorter in female sex and negative microscopy.

Conclusion: The serology using CIE presented a strong association with clinical response, making it a valuable method for monitoring patients with PCM. Most patients achieved CIE titres ≤ 1:4 during antifungal therapy, which was strongly associated with a successful clinical response.