increasing the awareness of appropriate risk-reduction activities and possible symptoms of RBF among persons who have exposure to rats. Intravenous penicillin is the treatment of choice, and prompt therapy can prevent severe complications $ (1) $ . Because rapid laboratory confirmation of infection with S. moniliformis might not be possible, clinicians should consider initiating empiric therapy for patients with a compatible clinical presentation and exposure history.

Clinicians should consider RBF in the differential diagnosis for unexplained febrile illness or sepsis in patients reporting rat exposure. Initial symptoms might be nonspecific (Box), but a maculopapular rash and septic arthritis commonly develop $ (1,5) $ . However, as demonstrated by the cases in this report, patients can have severe disease before the onset of typical symptoms. Despite its name, approximately 30% of patients with RBF do not report having been bitten or scratched by a rat $ (1,5) $ . Risk factors for RBF include handling rats at home and in the workplace (e.g., laboratories or pet stores). RBF is rare in the United States, with only a few cases documented each year $ (1,6,7) $ . However, because RBF is not a nationally notifiable disease, its actual incidence has not been well described.

In the cases described here, diagnosis of RBF was delayed in part because of the inability to rapidly isolate or identify S. moniliformis. If infection with S. moniliformis is suspected, specific media and incubation conditions should be used (8) (Box). In the absence of a positive culture, identification of pleomorphic gram-negative bacilli in appropriate specimens might support a preliminary diagnosis (1). In the event of an unexplained death in a person with rat exposure, performing an autopsy might also be critical to identifying an etiology.

Because of the high prevalence of colonization and asymptomatic infection with S. moniliformis among rodents (Box), testing and treatment of rats is not practical. Disease prevention should center on risk reduction among persons with frequent rat exposure. Adherence to simple precautions while handling rats can reduce the risk for RBF and other potential rodent-borne zoonotic infections, wound infections, and injuries. Persons should wear gloves, practice regular hand washing, and avoid hand-to-mouth contact when handling rats or cleaning rat cages (1,9). If bitten by a rat, persons should promptly clean and disinfect the wound, seek medical attention, and report their exposure history. A tetanus toxoid booster should be administered if $ \geq $ 10 years have lapsed since the last dose (9,10).

Clinicians should contact their state health departments for assistance with diagnosis of unexplained deaths or critical illnesses and cases or clusters of suspected RBF or other zoonotic infections. UNEX coordinates surveillance for unexplained deaths possibly attributed to infection throughout the United States. Cases are reported by a network of health departments, medical examiners/coroners, pathologists, and clinicians. Epidemiologic and clinical data are collected, and available clinical and pathologic specimens are obtained for reference and diagnostic testing at state, CDC, and other laboratories. State and local health departments may contact UNEX for assistance with the evaluation of unexplained deaths that occur in their jurisdictions.

## References

1. Washburn RG. Streptobacillus moniliformis (rat-bite fever). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious diseases. 5th ed. New York, NY: Churchill Livingstone; 2000:2422–4.

2. McHugh TP, Bartlett RL, Raymond JI. Rat-bite fever: report of a fatal case. Ann Emerg Med 1985;14:1116--8.

3. Sens MA, Brown EW, Wilson LR, Crocker TP. Fatal Streptobacillus moniliformis infection in a two-month-old infant. Am J Clin Pathol 1989;91:612–6.

4. Shvartsblat SS, Kochie M, Harber P, Howard J. Fatal rat-bite fever in a pet shop employee. Am J Ind Med 2004;45:357–60.

5. Graves MH, Janda MJ. Rat-bite fever (Streptobacillus moniliformis): a potential emerging