Chronic pulmonary aspergillosis (CPA), caused by Aspergillus spp., mainly affects immunocompetent individuals with underlying structural lung disease, particularly those with prior tuberculosis. Although the Aspergillus IgG ELISA test has higher sensitivity, precipitation methods such as immunodiffusion (ID) and counterimmunoelectrophoresis (CIE) are still widely used in low- and middle-income countries. This study aimed to characterize the serological response assessed by CIE over one year of antifungal treatment.

CPA cases were defined according to ESCMID/ERS criteria (2016). Serological tests performed at the Institute of Tropical Medicine of the University of São Paulo between 2014 and 2022 were included. Serological response was evaluated throughout one year of antifungal therapy, and clinical response was assessed at the end of follow-up. Categorical variables were described as absolute numbers and percentages, and quantitative variables as median and interquartile range (IQR).

The study included 42 patients, predominantly male (n = 28; 67%), with a median age of 54 years (IQR 44–61). The main underlying comorbidity was pulmonary tuberculosis (n = 30; 71%). Only one patient was HIV-positive (2%), and none had malignancy. Most patients had bilateral disease (82%), radiological aspergilloma (56%), and cavitary disease (82%). All patients received antifungal therapy: itraconazole in 32 cases (76%) and voriconazole in 10 (24%). The median duration of antifungal treatment was 12 months (IQR 9.5–13). Nine patients (21%) underwent surgery. The median number of serological tests per patient was 3.5 (IQR 3–5), totaling 155 serologies. The median CIE titer at treatment initiation was 1:24 (IQR 1:8–1:32), with a progressive decline in subsequent measurements: 1:12 (1:4–1:32), 1:8 (1:4–1:32), 1:8 (1:2–1:32), and 1:4 (1:2–1:8). Only one patient (2%) showed clinical worsening, while the others remained stable (n = 9; 21%) or improved clinically (n = 32; 76%).

Similar to Aspergillus IgG measured by ELISA, CIE serology showed good correlation with response to antifungal treatment, demonstrating a progressive decline in titers during follow-up. These findings suggest that CIE may be a useful alternative method for therapeutic monitoring, especially in resource-limited settings, helping to define the appropriate timing for antifungal discontinuation.