Case Presentation: A 71 year-old woman with a past medical history of hypertension was admitted with generalized fatigue, weakness, and decreased concentration and memory for a week and a half. During this time, she also had fevers, sweats, anorexia and nausea. She was originally admitted to an outside hospital after falling and losing consciousness, diagnosed with a viral illness and dehydration, and discharged. However, her fevers and chills continued; a clinic referred her to the hospital for abnormal labs, weakness, and dizziness, with new-onset unintentional weight loss, myalgia, difficulty urinating, facial swelling, odynophagia and a new rash on her chest. On admission, her examination revealed fever, tachypnea, and mild tachycardia. She also had a grade II/VI systolic ejection murmur at the right upper sternal border and an erythematous maculopapular rash on her chest, abdomen, and right leg. She began empiric Zosyn and vancomycin on admission.
Laboratory studies revealed hyponatremia, elevated creatinine, mildly elevated AST and ALT, mild leukocytosis, and anemia. On the second day, doxycycline was started to cover an atypical infection after further questioning revealed that she had 10 cats and 5 dogs with fleas, with no known tick bites. Infectious Disease consultation assisted with the diagnostic workup. With clinical improvement and the return of negative cultures, vancomycin and subsequently Zosyn were discontinued. Defervescence after doxycycline initiation, along with high clinical suspicion for an intracellular infectious etiology, prompted continuation of doxycycline for a total of 14 days, although Rickettsia typhi, spotted fever and ehrlichia antibodies came back negative. She was discharged after a 13 day hospital course; one week later, Rickettsia typhi antibodies seroconverted to positive, with IgG of 1:64 and IgM of 1:256.
Discussion: Patients with murine typhus, a disease that is not uncommon and is easily treatable with doxycycline, may not be immediately seropositive. Appearance of an IgM antibody response, with a cutoff of 1:64, normally occurs 7-14 days after disease onset, but in this case appeared 3-4 weeks following disease onset. This testing is done with immunofluorescence antibody assay, which is considered the gold standard for serologic testing for rickettsial diseases and is estimated to have a sensitivity of 94-100% after 14 days.
Conclusions: Negative Rickettsia typhi antibody serology should not cause physicians to prematurely rule out murine typhus, particularly when clinical suspicion remains high.