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ACEP Now features one article each issue related to an ACEP eCME CME activity.
The Case
Chief complaint: fever and rash. I stare at the triage notes of the eight-year-old female I had just picked up. Overwhelmed by the vast differential that comes to mind, I decide to approach the case by first ruling out the most life-threatening diagnoses, such as meningococcemia and Stevens-Johnson syndrome, even though they are highly unlikely in my patient.
As an EM intern, I’m still developing a sense for distinguishing “sick” versus “not sick,” but upon entering my patient’s room, I know immediately this girl is “sick.” A thin, pale child lies before me, splayed out on the stretcher and holding her right arm across her chest. She doesn’t even look up when I introduce myself. A morbilliform rash peeks through her gown, and I notice the rash on her face, extremities, palms, and soles (see Figure 1). “Palms and soles…” I recall the more-focused differential for a palms/soles rash: meningococcemia; Rocky Mountain spotted fever; hand, foot, and mouth disease; secondary syphilis…
The parents describe their child as becoming progressively more “lethargic” and febrile over the past week (Tmax 104°F). They had already visited the pediatrician three times but decided it was time to come to the ED when the patient woke up refusing to walk due to pain in her knees and ankles. Delving into my bank of fever questions, I ask about headache, neck stiffness, skipped vaccinations, sick contacts, recent travel, or any new medications. However, all of these questions return negative. Fever, rash, joint pain—what else could I ask? At a loss, I decide to ask about any known tick bites, though this is unlikely because we are at the peak of winter in New England. Still negative. Any new pets? Well, now that I mention it, they admit to buying a new pet rat a few weeks ago.
(click for larger image) Figure 1. Morbilliform rash
On exam, the patient appears very fatigued. Her vital signs are significant for a fever of 38°C and heart rate of 126 bpm. Her respiratory rate, blood pressure, and SpO2 are within normal limits. The most striking exam findings are the patient’s pallor contrasted against a blanching morbilliform rash over her face, extremities, palms, and soles but sparing her torso. I also notice a petechial rash developing on the patient’s legs that I hadn’t seen previously. Despite mild postauricular lymphadenopathy, the rest of her head, eyes, ears, nose, and throat exam is normal. Her heart, lung, and abdomen exams are also normal. However, when I attempt to move the patient’s right shoulder and ankles, she moans in pain.
Rat-Bite Fever
As I return to my desk, the history of a new pet rat continues to resonate in my mind. I search the Internet for rat-borne diseases, and a recent news article appears as one of the top search results.1 The article describes the case of a young boy misdiagnosed with a viral illness, but worsening of his symptoms resulted in his death a few days later. On autopsy, the boy was found to be infected with the bacterium causing rat-bite fever (RBF), Streptobacillus moniliformis.
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.
Dr. Vetter is a resident in emergency medicine at the University of Connecticut in Hartford.
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Diagnosis and Treatment
S. moniliformis is an extremely fastidious organism that requires special conditions and culture media to grow. When drawing blood cultures, collect aerobic cultures in a purple-top tube, as the anticoagulant, sodium polyanethol sulfonate, in most aerobic culture bottles inhibits the growth of S. moniliformis. Alert the lab that you suspect the organism, which requires enriched trypticase soy agar or broth, and request that the cultures be held for up to two weeks, as the bacteria grow very slowly.4 However, because of the difficulty in confirming diagnosis by culture, the diagnosis is often made by history, and empiric antibiotic treatment should be started immediately due to the high complication and fatality rate. Penicillin is the treatment of choice or doxycycline (as used in my patient) for penicillin-allergic patients.
- DOSING (ADULTS)
- IV penicillin G: 200,000 units every 4 hours for 5–7 days (can be switched to PO once patient shows clinical improvement)
- PO penicillin V: 500 mg QID, to complete a 14-day treatment course
- Doxycycline (for PCN-allergic patients): IV or PO 100 mg BID for 14 days
- DOSING (CHILDREN)
- IV penicillin G: 100,000–150,000 units/kg/day, divided in 4 doses, up to maximum 8 million units/day, for 5–7 days (can be switched to PO once patient shows clinical improvement)
- PO penicillin V: 25–50 mg/kg/day, divided in 4 doses, up to maximum 2g/day, to complete a 14-day treatment course
- Doxycycline (for PCN-allergic patients): 2–4 mg/kg/day IV or PO, divided in 2 doses, for 14 days
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References
- Adam JK, Varan AK, Pong AL, et al. Notes from the field: fatal rat-bite fever in a child—San Diego County, California, 2013. Morb Mortal Wkly Rep. 2014;63:1210-1211.
- Pickering LK, Baker CJ, Kimberlin DW, et al. Red book: 2009 report of the Committee on Infectious Diseases. 28th ed. Elk Grove Village, Ill: American Academy of Pediatrics; 2009:299-300.
- US Department of Health and Human Services. Rat-bite fever (RBF). 2012. Available at: www.cdc.gov/rat-bite-fever/health-care-workers/index.html. Accessed Feb. 16, 2015.
- Elliott SP. Rat bite fever and Streptobacillus moniliformis. Clin Microbiol Rev 2007;20:13-22.