A. Rat Bite Fever
What did you learn in medical school in your Peds rotation? take a social history – including asking about pets. The family disclosed that the patient has a pet rat which he plays and kisses regularly!
The patient was admitted to hospital and started on IV penicillin. ID and Rheumatology were consulted and agreed that the clinical symptoms consistent with Rat Bite Fever. The clinical course was complicated by a right septic hip which necessitated arthrotomy on hospital day 15. The there was no growth from blood and joint cultures the patient ultimately improved – though it took two and a half weeks.
Rat Bite Fever (RBF) is caused by Streptobacillus moniliformis or Spirillum minus. RBF typically presents after approximately 3-10 days following contact with the bacteria. It can be up to 21 days. Classically, 2-4 days after the onset of fever a rash appears. It is characteristically flat and red with small bumps – but this morphologically variable exanthema can be maculopapular, purpuric or petechial mostly occurring on the distal extremities including the palms and soles. About 50% of patients develop migratory polyarthralgias. Additional symptoms can include vomiting, headache, muscle pain and sore throat.
Symptoms may resolve without treatment, but serious complications of RBF include: solid-organ abscesses, septic arthritis, pneumonia, hepatitis, nephritis, meningitis, endocarditis, myocarditis, pericarditis. If untreated, case fatality is 7-13% – and yes, fatal cases have been reported in children. Penicillin is the treatment of choice in suspected or confirmed cases.
Microbiological diagnosis can be difficult due to specific conditions required for growth. Anticoagulant contained in many aerobic culture bottles can inhibit growth, thus anaerobic media can result in higher yields. PCR testing is showing promise as another potential diagnostic option.
American Academy of Pediatrics. Rat-Bite Fever. In: eds. Red Book: 2021–2024 Report of the Committee on Infectious Diseases. American Academy of Pediatrics; 2021; 627-628
CDC. “Information for Health Professionals and Laboratory Personnel | Rat-Bite Fever (RBF) | CDC.” Center for Disease Control and Prevention, 18 Jan. 2019, www.cdc.gov/rat-bite-fever/health-care-workers/index.html.
Elliott, Sean P. “Rat bite fever and Streptobacillus moniliformis.” Clinical microbiology reviews vol. 20,1 (2007): 13-22. doi:10.1128/CMR.00016-06