Selection bias and inferential validity in fever of unknown origin studies. Comment on: Poposki et al. Visceral leishmaniasis as a leading cause of fever of unknown origin in immunocompetent adults.

The article by Poposki et al. on visceral leishmaniasis as a cause of fever of unknown origin presents clinically valuable observations but exhibits substantial methodological limitations. Differential exclusion of undiagnosed cases introduces selection bias and precludes generalizable prevalence estimates. The analytical strategy lacks etiological coherence by comparing a specific diagnosis against heterogeneous conditions. Multiple univariate comparisons without adjustment for family-wise error rate and absence of multivariable analysis to control confounding limit causal inference. The cross-sectional assessment of clinical features after diagnostic confirmation precludes temporal inference. Future studies would benefit from nested case-control designs, transparent reporting of diagnostic pathways, and appropriate statistical adjustment.