Diagnostic performance of a loop-mediated isothermal amplification test for the diagnosis of human and cat sporotrichosis in two highly endemic areas in Brazil: insights from a real-world, field-based evaluation.

Sporotrichosis is a subacute to chronic mycosis of major public health relevance in endemic regions, affecting both humans and animals, particularly cats. Rapid and accessible diagnostic tools are urgently needed to improve case detection and disease surveillance. Thus, this study aimed to validate a previously described loop-mediated isothermal amplification (LAMP) assay for the diagnosis of sporotrichosis in clinical samples from humans and cats obtained in two highly endemic areas in Brazil. We conducted an observational study including human patients and cats with suspected sporotrichosis. Analytical sensitivity and specificity were initially assessed using reference strains of Sporothrix spp. The diagnostic performance of the LAMP assay was then evaluated in clinical samples at different incubation times and compared with culture results. Sensitivity, specificity, and additional diagnostic parameters were calculated separately for human and cat cases. The LAMP assay was able to detect the three major Sporothrix species associated with sporotrichosis, with higher analytical sensitivity for S. brasiliensis. However, when applied to human clinical samples, the assay showed limited sensitivity and specificity, particularly at earlier incubation times, resulting in poor overall diagnostic performance. In contrast, performance in cat samples was comparatively higher but still affected by false-positive and false-negative results. Despite promising analytical characteristics and previous success in experimental models, this LAMP protocol demonstrated limited diagnostic utility for human and cat sporotrichosis under real-world clinical conditions, highlighting the need for further optimization and rigorous clinical validation before implementation in routine practice.