When a child develops a fever, determining whether the cause is a bacterial or viral infection can be difficult. The distinction is important because bacterial infections may require antibiotics, while antibiotics do not work against viruses. When the cause of an infection is uncertain, antibiotics may be prescribed unnecessarily, contributing to the growing problem of antibiotic resistance.

Researchers are investigating whether molecules called microRNAs, or miRNAs, could provide a faster and less invasive way to identify the type of infection. miRNAs are short RNA molecules that help regulate gene activity. They can be found in body fluids, including blood and urine, and some remain stable enough to serve as potential biomarkers of disease.

Researchers at Riga Stradiņš University in Latvia examined whether miRNAs found in urine could help distinguish bacterial infections from viral infections in children.

Outline of the main study workflow

22 pediatric patients aged one month to 18 years were included in the study, comprising seven with proven bacterial infections, seven with proven viral infections, and eight controls without signs of infection. RNA-seq was performed for both blood and urine samples, generating full transcriptome RNA-seq data and small RNA-seq data consecutively.

The researchers analyzed samples from 22 children. Seven had bacterial infections, seven had viral infections, and eight children without infection served as controls. Small RNA sequencing was used to examine miRNAs in urine, while RNA sequencing of the full transcriptome was used to measure gene activity in blood.

The team then used statistical methods to identify combinations of urinary miRNAs that differed among the groups. One analysis identified a signature consisting of five miRNAs that showed a strong ability to distinguish the groups within the available dataset.

The five-miRNA signature produced an internal area under the curve, or AUC, of 0.981. AUC is a measure commonly used to evaluate how well a diagnostic approach separates different groups, with values closer to 1 indicating better discrimination. However, the researchers emphasized that the small number of participants resulted in wide confidence intervals, meaning the apparent performance must be confirmed in larger groups of patients.

The researchers also compared changes in urinary miRNAs with changes in gene expression detected in blood. By combining correlation analysis with predictions of which genes the miRNAs might regulate, they identified related molecular patterns across the two types of samples.

Many of these patterns were associated with immune functions involved in responding to infection, including cytokine signaling and T-cell activation. Cytokines are signaling molecules that help immune cells communicate, while T cells play important roles in coordinating immune responses and eliminating infected cells.

The results suggest that urinary miRNAs may provide information about how the body is responding to different types of infection. Because urine collection is non-invasive, a urine-based biomarker test could be particularly useful in children, where repeated blood collection can be more difficult.

The findings are preliminary. Only 22 children were included, and the five-miRNA signature was evaluated within the same small dataset used to identify it. Larger, independent groups of patients will be needed to determine whether these biomarkers can reliably distinguish bacterial from viral infections in real clinical settings.

If validated, combining RNA sequencing with urinary miRNA analysis could eventually contribute to diagnostic tests that help clinicians identify the likely cause of a fever more quickly. More accurate identification of bacterial and viral infections could support appropriate treatment decisions while reducing unnecessary antibiotic use.