Etiologic diagnosis of Capnocytophaga canimorsus meningitis by broad-range PCR

Abstract

Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae account for approximately 80% of the cases of acute bacterial meningitis [1]. Since the introduction of H. influenzae type b vaccination, however, H. influenzae meningitis has become rarely seen. Capnocytophaga canimorsus is an even less-frequent cause of bacterial meningitis, with only 19 cases having been published so far in the English-language literature [2]. However, since it is fashionable for humans to own animals as pets and for defense, the true incidence of this pathogen may be higher. Reported here is the case of a patient with bacteremia and meningitis after a dog bite, in which the etiologic diagnosis was difficult to establish. A previously healthy 54-year-old Caucasian man who regularly consumed alcohol (approximately 85 g ethanol/ day) was admitted to the emergency room with a 3-day history of increasing headache and chills, associated with vomiting, diarrhea, and arthralgia. He had been bitten on his left index finger by his pet dog 10 days prior to presentation. Physical examination showed a temperature of 38.6°C, blood pressure of 120/80 mmHg and pulse rate of 100 beats/min. He was alert and oriented. Flexion of the cervical spine was painful, but there were no focal neurological deficits. Laboratory findings revealed an elevated level of Creactive protein (193 mg/l), leukocytosis (12.9×10/l with 32% of neutrophils showing band forms), a decreased platelet count (56×10/l) and a normal international normalized ratio value (1.0). Lumbar puncture showed turbid cerebrospinal fluid (CSF) with 1001 leukocytes/μl (82% neutrophils), an elevated protein level (1.69 g/l) and low glucose concentration (1.8 mmol/l or 30% of the blood glucose concentration). Even though no microorganisms were seen in a Gram-stained specimen of CSF, the diagnosis of bacterial meningitis was made. Empirical antibiotic therapy with ceftriaxone and a 4-day course of intravenous dexamethasone were initiated. Gram-negative bacteria grew in both the CSF culture media and in an aerobic blood-culture flask, after 5 and 7 days, respectively. Further differentiation of the bacteria was not possible and the colonies were sent to the reference laboratory for further testing. After failing to subculture the colonies, identification was achieved using broad-range polymerase chain reaction (PCR) and analysis of 16S ribosomal DNA sequences of the colonies, as described previously [3]. The molecular identification revealed C. canimorsus (Fig. 1). Retrospective Gram stain of the colonies showed gram-negative rods with fusiform shapes suggestive of a Capnocytophaga sp. Our patient’s condition improved rapidly on ceftriaxone therapy, which was administered for 13 days, and he was discharged 1 day after treatment ended. C. canimorsus is a slow-growing, capnophilic, gramnegative rod that was first isolated in 1976. Its initial name DF-2 (dysgonic fermenter) [4] was changed to C. canimorsus, [5] since canimorsus is Latin for dog bite and the bacterium is part of the normal oral flora of dogs. In a previous study, Westwell et al. [6] were able to isolate C. canimorsus from the oral cavity of 24% of 180 dogs and 17% of cats. Most patients with C. canimorsus infection report an antecedent dog bite (54%), scratch (8.5%) or at least contact (27%) [7]. On average, 7 days pass between the time of the dog bite and hospitalization (range, 3–14 days) [2], and the clinical presentation spans from mild to severe disease. Host risk factors for a fulminant clinical course, i.e. meningitis or sepsis with shock and disseminated intravascular coagulation, include asplenia, alcoholism, and immunosuppression with glucocorticoid or chemotherapy [8]. However, in 37% of patients with C. canimorsus meningitis no such risk J. Gottwein . T. Herren (*) Department of Medicine, Limmattal Hospital, Urdorferstrasse 100, 8952 Schlieren, Switzerland e-mail: thomas.herren@spital-limmattal.ch Tel.: +41-44-7332843 Fax: +41-44-7332899