Epidemiologic Notes and Reports Rat-Bite Fever in a College Student--California

On January 19, 1984, a suspected case of rat-bite fever (RBF) was reported to the San Bernardino County (California) Department of Public Health. The patient, a 54-year-old female undergraduate psychology student, had been bitten on the dorsal and ventral aspects of the middle phalanx of the left index finger by a laboratory rat on January 9. She was immediately referred to the student health center, where the wound, described as a clean puncture, was cleansed, and tetanus toxoid was administered. The patient was sent home with orders to soak her finger in hot, soapy water, but within 12 hours, the finger was swollen and throbbing. She returned to the student health center the following day and was admitted to a local hospital.

Physical examination revealed an afebrile patient with erythema and swelling along the flexor tendon from the proximal interphalangeal joint extending downward over the palm of the hand into the thenar eminence. Axillary lymph nodes were enlarged. Admission white blood cell count was 7,200/mm((3)), with a differential of 69 neutrophils, 26 lymphocytes, four monocytes, and one eosinophil. Urinalysis was normal.

Initial cultures (on January 10) of blood and exudate obtained from the wound were negative. The patient was allergic to penicillin and was placed on erythromycin 500 mg every 6 hours for 48 hours because of possible staphylococcal or streptococcal infection. Between January 10 and January 12, the patient developed a fever (38.3 C (101.4 F)), shaking chills, arthralgia, mild nausea, generalized petechial rash, and headache and reported that her finger was exquisitely sensitive.

On January 12, the tendon sheath was surgically drained, and the patient was placed on clindamycin intravenously 450 mg every 6 hours for 48 hours. Within 24 hours, her temperature became normal, and the axillary nodes decreased in size. On January 14, the hospital laboratory reported isolation of a branching Gram-negative rod from tissues collected at surgery; the organism was later identified as Streptobacillus moniliformis by the state's Microbial Diseases Laboratory. The organism failed to grow in the API 20E system (a microtube system designed for the identification of Enterobacteriaceae and certain other Gram-negative bacteria) and did not grow when tested for antimicrobial susceptibility using the Kirby-Bauer method.

On January 14, the patient was discharged from the hospital and placed on tetracycline 500 mg every 6 hours for 8 days. No relapses have been reported. Reported by AF Taylor, MPH, TG Stephenson, MPH, HA Giese, MD, GR Pettersen, MD, San Bernardino County Dept of Public Health, RA Murray, DrPH, California Dept of Health Svcs; Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: RBF is a single designation for two diseases with clinical and epidemiologic similarity (1). Streptobacillary RBF, caused by S. moniliformis (2), has an incubation period of 3-10 days, a rapidly healing point of inoculation (i.e., the rat bite), and abrupt onset of irregularly relapsing fever, shaking chills, vomiting, headache, arthralgia, myalgia, and regional lymphadenopathy (3-7). Shortly after onset, a maculopapular rash appears on the extremities. Anemia, endocarditis, and myocarditis have also been reported. Spirillary RBF, caused by Spirillum minus, has a longer incubation period (1-3 weeks), and the wound may reappear at the time of onset of systemic illness. The case-fatality rate for RBF may approach 10% for untreated cases (2-6). In the present case, the shortened incubation period and suppurative nature of the wound may indicate streptobacillary RBF mixed with some other unidentified pathogen.

RBF is a rare disease in the United States, but since it is not reportable, no true measure of its incidence exists. Most cases of RBF, including those acquired in the laboratory, follow rat bites (3); however, exposure to other domestic and wild animals has also resulted in disease (4,6). Infection has also followed consumption of contaminated raw milk (8). The rate of nasopharyngeal carriage of S. moniliformis by healthy laboratory rats has been reported to vary between 10% and 100% (3). In view of the likely high rates of exposure of laboratory personnel to S. moniliformis, three possible explanations for the rarity of diagnosis of RBF are: a true low incidence of disease in spite of common exposure, a low index of suspicion of attending physicians, and the strict growth requirements of the organism.

Recommended therapy for RBF is penicillin, with streptomycin or tetracycline as alternatives (6). Before diagnosis, the patient reported here was treated with erythromycin but without clinical improvement; she responded rapidly to intravenous clindamycin in conjunction with surgical drainage of her wound. Use of clindamycin for streptobacillary RBF has been reported (3), but detailed in vitro or clinical efficacy studies have not been performed. Two isolates of S. moniliformis tested for antimicrobial susceptibility at CDC were sensitive to clindamycin; one of the two was resistant to erythromycin (9).

References

1. Martone WJ, Patton CM. Rat-bite fever. In: Balows A, Hausler WJ Jr, eds. Diagnostic procedures for bacterial, mycotic and parasitic infections. 6th ed. Washington, D.C.: American Public Health Association 1981:581-6.

2. Carbeck RB, Murphy JF, Britt EM. Streptobacillary rat-bite fever with massive pericardial effusion. JAMA 1967;201:703-4.

3. Anderson LC, Leary SL, Manning PJ. Rat-bite fever in animal research laboratory personnel. Lab Anim Sci 1983;33:292-4.

4. Taber LH, Feigin RD. Spirochetal infections. Pediatr Clin North Am 1979;26:377-413.

5. Raffin BJ, Freemark M. Streptobacillary rat-bite fever: a pediatric problem. Pediatrics 1979;64:214-7.

6. Gill FA. Streptobacillus moniliformis (rat-bite fever). In: Mandell GL, Douglas RG Jr, Bennett JE. Principles and practice of infectious diseases. Vol 2. New York: John Wiley & Sons, 1979;1806-9.

7. Cole JS, Stoll RW, Bulger RJ. Rat-bite fever. Report of three cases. Ann Intern Med 1969;71:979-81.

8. Place EH, Sutton LE Jr. Erythema arthriticum epidemicum (Haverhill fever). Arch Intern Med 1934;54:659-84.

9. CDC. Unpublished data.

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