Sporadic Human Infections With <i>Rickettsia japonica</i> in Yichang, China, 2021–2023

Japanese spotted fever (JSF) is an easily neglected infectious disease, where misdiagnosis and delayed treatment significantly contribute to poor prognoses in affected patients. Our prospective observational study (2021-2023) systematically characterized 56 JSF cases in Yichang through tripartite analysis encompassing epidemiological distributions, clinical phenotyping, and phylogenetic relationship analysis of <i>Rickettsia japonica</i> (<i>R. japonica</i>). Our study delineated distinct clinical presentations of JSF, and identified five laboratory indexes demonstrating significant associations with disease severity. Notably, thrombocytopenia (platelet deficiency) and procalcitonin (PCT) levels emerged as critical indicators, with PCT as a well-characterized inflammatory mediator showing particular prognostic value for anticipating severe complications in rickettsial infections, consistent with prior pathophysiological research. Phylogenetic analysis revealed that <i>R. japonica</i> strains distributed in Yichang City exhibited extremely low genomic diversity. Further, the <i>R. japonica</i> strains isolated in our study exhibited a high degree of homology with <i>R. japonica</i> isolation within the borders of China. In summary, our research identified several factors that indicate a high risk of poor outcomes in <i>R. japonica</i> infections. Additionally, we observed highly similar phylogenetic relationships among <i>R. japonica</i> strains, which have important implications for disease prevention, control, and clinical diagnosis.