Rocky mountain spotted fever (RMSF) causes significant illness and death in children. Although historically rare in California, USA, RMSF is endemic in areas of northern Mexico that border California. We describe 7 children with RMSF who were hospitalized at a tertiary pediatric referral center in California during 2017–2023. Five children had recent travel to Mexico with presumptive exposure, but 2 children did not report any travel outside of California. In all 7 patients, Rickettsia rickettsii DNA was detected by plasma microbial cell-free next-generation sequencing, which may be a useful diagnostic modality for RMSF, especially early in the course of illness, when standard diagnostic tests for RMSF are of limited sensitivity. A high index of suspicion and awareness of local epidemiologic trends remain most critical to recognizing the clinical syndrome of RMSF and initiating appropriate antimicrobial therapy in a timely fashion.

落基山斑疹热 （RMSF） 会导致儿童患上严重疾病和死亡。虽然 RMSF 在美国加利福尼亚州历史上很少见，但在墨西哥北部与加利福尼亚接壤的地区流行。我们描述了 7 名 RMSF 儿童，他们在 2017-2023 年期间在加利福尼亚州的三级儿科转诊中心住院。5 名儿童最近曾前往墨西哥旅行，并推定接触，但 2 名儿童未报告任何加州以外的旅行。在所有 7 例患者中，通过血浆微生物游离细胞下一代测序检测到立克次体 DNA，这可能是 RMSF 的有用诊断方式，尤其是在病程早期，此时 RMSF 的标准诊断测试敏感性有限。高度怀疑和对当地流行病学趋势的认识对于识别 RMSF 的临床综合征和及时开始适当的抗菌治疗仍然最为关键。