Rat-bite Fever, Canada

To the Editor: Rat-bite fever was once considered an infection exclusive to children living in poverty; however, dense urban housing and changing pet-keeping practices may be altering this profile (1,2). To date, ≈200 cases of rat-bite fever have been reported in the United States (3), and a recent study reported a 2-fold increased incidence in California during the 1990s (1). We report on 2 cases that occurred in Ontario, Canada, in the early 2000s. The first case occurred in a previously healthy 29-year-old man who was bitten on the finger by a pet rat. The wound healed spontaneously. After 24 hours, fever and emesis developed ; 4 days later, diffuse maculopapu-lar rash and migratory arthritis of the knees, ankles, and finger joints ensued. Physical examination showed a macu-lopapular rash over the lower extremities , an effusion of the left knee, and a warm, erythematous left ankle. Laboratory investigations showed hemoglobin level of 134 g/L, leuko-cyte count of 16.0×10 9 /L, and neu-trophil count of 13.8×10 9 /L. Aspiration of the knee produced 70 cm 3 of cloudy fluid; synovial fluid analysis showed 666×10 6 /L leukocytes with a predominance of neutrophils. Ceftriaxone, 2 g once a day, was given intravenously for 7 days. Although symptoms improved within 24 hours, the effusion recurred within 48 hours of discontinuing the initial course of ceftriaxone. The knee was surgically drained, and ceftriaxone was continued for 5 weeks. Systemic symptoms and the effusion resolved. The second case occurred in a previously healthy 9-year-old girl who had mucosal contact with a pet rat. She sought treatment after 7 days of generalized maculopapular and pustu-lar rash and 10 days of fever and headache. She had an associated asymmetric, migratory arthritis. Physical examination showed superficial scratches from the rat; temperature of 39.6°C; heart rate of 102 bpm; swelling, erythema, and decreased range of motion in several joints; and pustular lesions on the soles of the feet. The patient's leukocyte count was 8.3×10 9 /L. Synovial fluid from the knee showed 45.5×10 6 /L leukocytes with 89% neutrophils; the culture showed no growth. Gram stains of blood and pustule swabs showed large, pleomorphic, gram-negative bacilli with long filaments and irregular swellings. Growth occurred on the blood culture after 28 hours of aerobic incubation at 35°C in 10% horse serum. Characteristic puff-ball colonies of Streptobacillus monili-formis were seen in supplemented thioglycolate broth. Identification of the organism was confirmed by …