Severe Rickettsioses in Critically Ill Adults: Clinical Presentations and Diagnostic Pathways in a Hospital-Wide Case Series

Introduction Severe rickettsioses may progress from nonspecific febrile illness to shock, respiratory failure, neurological dysfunction, and multiorgan failure, while classical cutaneous or exposure clues may be absent. We characterized the clinical presentations, diagnostic pathways, organ-support requirements, and short-term outcomes of critically ill adults with severe rickettsioses identified through hospital-wide screening. Methods We conducted a retrospective hospital-wide case series at the First Affiliated Hospital, Zhejiang University School of Medicine, from January 1, 2020 to September 24, 2026. Adults were eligible if mNGS detected Rickettsia spp. or Orientia tsutsugamushi in a clinically relevant specimen, the clinical syndrome was concordant with the organism, and infection-associated critical illness required ICU-level management. Clinical features, microbiological findings, antimicrobial treatment, organ support, and hospital outcomes were reviewed. Results Five patients met the eligibility criteria; all were women aged 55–74 years. Three had Rickettsia japonica infection and two had O. tsutsugamushi infection. Presentations included septic shock, severe acute respiratory distress syndrome, neurological dysfunction, cardiopulmonary dysfunction, and acute kidney injury. Four patients required invasive mechanical ventilation, two received continuous renal replacement therapy, and one patient with Japanese spotted fever required venovenous extracorporeal membrane oxygenation. Blood mNGS identified the clinically relevant organism in four patients; R. japonica was additionally detected in bronchoalveolar lavage fluid in one. Cerebrospinal fluid mNGS identified O. tsutsugamushi in the patient with neurological involvement. All patients received doxycycline-containing therapy. Four completed hospitalizations survived to discharge; one patient remained hospitalized at the study cutoff. Conclusion Severe rickettsioses presented with heterogeneous forms of critical illness rather than a single ICU syndrome. Rickettsiosis should be considered in unexplained febrile multiorgan dysfunction, particularly with thrombocytopenia, hepatic abnormalities, or compatible outdoor exposure. mNGS provided useful etiologic evidence but required clinical and microbiological interpretation.