An exploratory clinical study of the diagnosis and staging of typhoid fever using label-free surface-enhanced Raman spectroscopy liquid biopsy.

Typhoid fever is a highly contagious tropical disease that requires early diagnosis to avoid rapid spread among communities and long-lasting effects on patients. Standard diagnostic protocols rely on microbial cultures and agglutination assays, which have inherent limitations, including low sensitivity, slow clinical results, and the need for often unavailable reagents and equipment in the regions of the outbreak. Label-free surface-enhanced Raman spectroscopy (SERS) is a promising chemical identification technology that can be performed in liquid samples. In this clinical study, we demonstrate the use of label-free SERS based on gold nanoparticles to diagnose and stage typhoid fever through liquid biopsy analysis of 30 patient serum samples and an unsupervised algorithm. Our method can discriminate between healthy and typhoid fever patient samples, as well as identify whether the disease is in an early or consolidated stage. Using only 15 spectra from each patient sample, label-free SERS correctly diagnosed and staged all tested samples (with a true positive rate of 1.00 and a clustering silhouette score of 0.6) as demonstrated by a cross-validation approach. Taken together, our method opens up new avenues for the accurate, rapid, and inexpensive diagnosis and staging of tropical diseases based on liquid biopsy samples.