The article further discusses the symptoms of RBF, which include fever (check), rash (check), and arthralgias (check) in a patient with exposure to rats (check). My attending and I are amazed how closely this diagnosis fits our patient. Upon further questioning, the patient denies any rat bites. However, she does admit to allowing the rat to lick her mouth and lips, much to my dismay. With guidance from a pediatric infectious disease specialist, we draw blood cultures and start empiric antibiotic therapy for RBF. The patient’s basic lab work returns at this point and is remarkable for a platelet count of 178K and C-reactive protein of 4.9 mg/L. The rest of her complete blood count, basic metabolic panel, liver function test, and erythrocyte sedimentation rate are within normal limits.

The patient is admitted to the hospital on IV doxycycline (2 mg/kg BID), and her symptoms begin to improve the following day. She is discharged within 48 hours, with increased energy, a fading rash, and no joint pain. She is instructed to continue PO doxycycline for two weeks. At follow-up one month later, the parents state their daughter is “perfect” and back to her normal self.

RBF is a rare but fatal bacterial illness in the United States caused predominantly by S. moniliformis, a gram-negative rod that is part of the normal respiratory flora of rodents.² It is spread to humans via a rat bite, scratch, or, in my patient’s case, a “kiss,” but it is susceptible to antibiotics such as penicillin or doxycycline (see sidebar for dosing). If misdiagnosed or left untreated, however, the disease carries a 13 percent mortality rate.³ Symptoms present anywhere from three to 21 days after rat exposure and include nonspecific symptoms such as fever, fatigue, headache, pharyngitis, and vomiting. These initial symptoms are followed by a rash, which is usually maculopapular, though it can be petechial or purpuric, and is most prominent on the extremities, palms, and soles. Polyarticular and asymmetric arthralgias develop in up to 50 percent of patients. When RBF is suspected, blood cultures should be drawn with specific instructions (see sidebar), as S. monilifomis is a fastidious organism.

Although RBF is a rare diagnosis, this case highlights the importance of taking a thorough history. Having a standard list of questions at your disposal to help sort out nonspecific symptoms, such as fever and rash, is crucial to avoid missing a fatal illness. Although it is unlikely I will encounter another case of RBF, this case serves as a reminder to maintain an open differential and to be less inclined to diagnose a viral illness without first considering other life-threatening diagnoses.