TOPIC: Critical Care TYPE: Fellow Case Reports INTRODUCTION: Hemophagocytic lymphohistiocytosis (HLH) is a syndrome characterized by cytokine storm and multi-organ failure with a mortality rate approaching 42% even when treated appropriately. HLH has a reported annual incidence of 1 in 800,000 with 90% being secondary HLH. Infections are the trigger in 20% of secondary HLH. Rickettsial triggers are limited to case reports in the pediatric population. We present a case of HLH secondary to Rickettsia rickettsii in a geriatric patient. CASE PRESENTATION: A 70-year-old diabetic male was admitted in the summer for 1 week of fevers, headaches, and progressing weakness. On admission, the patient had a waxing and waning mental status. He had anemia, thrombocytopenia, and kidney injury. CT abdomen showed mild splenomegaly. As part of an anemia work-up, a ferritin level was drawn and resulted at 7,044 ng/mL. At this time, HLH was added to the differential. A triglyceride level returned at 309 mg/dL.His mental status slowly deteriorated until he became unresponsive and intubated on hospital day 3. His platelet count dropped to 18,000/µL with a hemoglobin of 9 g/dL. Additionally, his creatinine increased to 9.28 mg/dL with a urea nitrogen of 120.7 mg/dL requiring renal replacement therapy. On day 5, IL-2 level returned at 21289 U/mL. However, the underlying etiology of his HLH was not clear. On day 6, the patient was started on doxycycline empirically as Rickettsial disease could not be ruled out. By day 7, the patient was interacting with caregivers. Following ventilator liberation, he confirmed that he frequently camps at a local lake with his last trip being 4 days prior to onset of fevers and headaches. The patient continued to gradually improve and was discharged to an acute rehab facility. Several days after his discharge, Rickettsia ricketssii IgM and IgG titers returned at 1:16384 and 1:2048, respectively. DISCUSSION: Rocky Mountain Spotted Fever (RMSF) has an incidence of 19-to-63 per million. Ricketsial infections rarely progress to HLH with variable outcomes depending on time of treatment. By our review, this complication has not been reported in adult patients. HLH secondary to infection has a favorable outcome compared to cases triggered by malignancy; however, mortality is heavily dependent on treatment of the underlying infection. Our patient's HLH resolved solely with treatment of the underlying infection and we suspect that this was due to early intervention. CONCLUSIONS: HLH carries a high mortality and has numerous triggers. While zoonotic triggers are a rare cause, the treatment can be simple and lifesaving. Early and aggressive diagnostic studies and treatment are imperative to surviving secondary HLH. REFERENCE #1: A. Hayden, S. Park, D. Giustini, A. Y. Y. Lee and L. Y. C. Chen, "Hemophagocytic syndromes (HPSs) including hemophagocytic lymphohistiocytosis (HLH) in adults: A sytematic scoping review," Blood Reviews, vol. 30, pp. 411-20, 2016. REFERENCE #2: M. R. George, "Hemophagocytic lymphohistiocytosis: review of etiologies and management," Journal of Blood Medicine, vol. 5, pp. 69-86, 2014. REFERENCE #3: S. C. Buckingham, G. S. Marshall, G. E. Schutze, L. E. R. Patterson and R. F. Jacobs, "Clinical and laboratory features, hospital course and outcome of rocky mountain spotted fever in children," The Journal of Pediatrics, vol. 150, no. 2, pp. 180-4, 2007. DISCLOSURES: No relevant relationships by Jason Thomas, source=Web Response No relevant relationships by Robert Walter, source=Web Response