THE CASE
A 72-year-old man was admitted to our Dallas hospital with a 4-day history of fevers and new-onset urinary frequency. He did not report any joint pain, sick contacts, or recent travel or recall any skin findings (rashes, insect bites). Past medical history was significant for hypertension, hyperlipidemia, diabetes, benign prostatic hyperplasia, recurrent urinary tract infections, and lumbar radiculopathy.
Initial signs and symptoms were suggestive of sepsis: a temperature of 102.7 °F, tachycardia, and a suspected genitourinary infection. This was supported by initial labs concerning for end-organ damage: elevated creatinine of 1.58 mg/dL (reference range, 0.67-1.17 mg/dL), elevated international normalized ratio (INR) of 1.6 (reference range, 0.9-1.1), hemoglobin of 12.8 g/dL (reference range, 13.5 - 17.5 g/dL), and platelet count of 99 ×109/L (reference range, 160-383 ×109/L).
Over the next several days, the patient’s condition worsened, and he experienced a decline in mental status, despite initiation of broad-spectrum antibiotics and fluid resuscitation. Although lumbar puncture was warranted, neither Neurology nor Interventional Radiology were willing to risk the procedure given the patient’s worsening hemoglobin (8.3 g/dL) and platelet count (51 ×109/L).
Preliminary work-up included a urinalysis negative for leukocytes, nitrites, and bacteria—despite a urine culture that showed gram-positive cocci. His chest x-ray was unremarkable, and computed tomography of his brain showed generalized atrophy without acute changes. The work-up was expanded to fungal cultures and immunochemical assays. Empiric treatment with micafungin and acyclovir was started without improvement.
Further conversation with family revealed that the patient liked to spend time outdoors and he’d had a similar episode in which he’d been diagnosed with an unknown disease from an insect bite. Pertinent negative tests included: HIV, syphilis, rapid heterophile antibody, influenza, respiratory virus panel, blood culture, fungal culture, antineutrophil cytoplasmic antibodies, histoplasmosis, brucellosis, malaria, Epstein-Barr virus, cytomegalovirus, and parvovirus. Coxiella burnetii and West Nile virus immunoglobulin (Ig) G were positive, suggesting a prior exposure.
THE DIAGNOSIS
Given these new findings and reported outdoor activities, Infectious Diseases recommended we start our patient on doxycycline for possible rickettsia infection. On Day 8, doxycycline 200 mg IV once daily was started. (The IV form was initiated due to the patient’s altered mentation.) The patient started to show improvement, and on Day 14, an immunofluorescence antibody (IFA) assay revealed Rickettsia typhi IgM titers 1:512 (< 1:64) and IgG titers 1:256 (< 1:64), consistent with a diagnosis of murine (endemic) typhus.
DISCUSSION
Murine typhus is an acute febrile disease caused by R typhi, an obligate, intracellular gram-negative organism.1 Worldwide, transmission to humans occurs mainly from infected rat fleas harbored by rodents. In the United States, it’s been suggested that opossums serve as an important reservoir in peri-domestic settings, with cat fleas as vectors.2-4 The disease is endemic to southern California and south Texas.4
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