Capnocytophaga canimorsus Sepsis Misdiagnosed as Plague -- New Mexico, 1992

Since 1961, 200 human isolates of Capnocytophaga canimorsus -- a gram-negative bacterium -- have been sent to CDC for identification. Infections with this organism may result in a spectrum of manifestations ranging from self-limiting cellulitis to fatal septicemia; most fatal infections have occurred in persons with a history of asplenia, alcoholism, or hematologic malignancy. In most (77%) cases, infection is preceded by a bite or other exposure to dogs (1). This report summarizes the investigation by the New Mexico Health and Environment departments and CDC of a fatal case of C. canimorsus infection in a resident of New Mexico. This case was initially misdiagnosed as human plague.

On June 4, 1992, a 50-year-old man developed epigastric pain, nausea, fever, chills, and a rash. On June 5, he developed rectal bleeding and was evaluated in an emergency room and hospitalized. On admission, his temperature was 92.8 F (33.8 C); other findings included petechiae and ecchymoses, epigastric rebound tenderness, and bright red blood in the rectum. The hematocrit was 28.4%; white blood cell count, 10,400 cells per mm3 with 53% bands; and platelet count, 16,000 cells per mm3. A Wright stain of the peripheral blood smear revealed rare intracellular rods within polymorphonuclear cells. The presumptive diagnosis was gram-negative sepsis and disseminated intravascular coagulation secondary to a mesenteric bowel infarction. He received multiple transfusions and was treated with intravenous antibiotics and an experimental monoclonal antiendotoxin antibody. An exploratory laparotomy on June 5 was normal; however, the patient developed acute renal failure and acute respiratory distress syndrome, and he died on June 7.

A postmortem examination performed by the New Mexico Office of the Medical Investigator revealed diffuse internal hemorrhage consistent with gram-negative sepsis. There was no evidence of underlying causes of immunosuppression. Because of the possibility of septicemic plague (sepsis due to Yersinia pestis), an aliquot of serum obtained on admission was tested on June 8 at New Mexico Health Department's Scientific Laboratory Division (SLD); the hemagglutination antiplague titer was 2048 (normal: less than 16). However, confirmatory testing of the buffy coat for plague immunofluorescent antibody (IFA) and of autopsy specimens was negative at the SLD and at CDC's plague laboratory in Fort Collins, Colorado. On June 9, blood cultures collected on admission grew a gram-negative rod that was identified as C. canimorsus on June 17. On June 23, SLD repeated the plague serologic testing of the original serum sample with new reagents; results were negative (titer=0).

An investigation indicated that on May 24 the man had been hiking in the mountains near his home but had no known history of insect or animal bites. He reported owning several dogs and consuming 4-6 alcoholic drinks per day. Additional history from the family indicated the man had a swollen, possibly infected, thumb at the time of admission; however, records from the postmortem examination did not indicate an infection of the thumb.

Because of the possibility of pneumonic plague, 15 hospital staff members received plague prophylaxis during the week following the presumptive diagnosis of human plague. An investigation by the New Mexico Environment Department did not identify plague-infected fleas on the man's dogs or in rodents living in the mountains where he had been hiking.

Reported by: G Lopez, MD, Las Cruces, New Mexico. T Brown, New Mexico Environment Dept. K Hatch, L Nims, G Oty, E Umland, MD, Scientific Laboratory Div; M Eidson, DVM, R Voorhees, MD, Div of Epidemiology, Evaluation, and Planning; CM Sewell, DrPH, State Epidemiologist, New Mexico Health Dept. Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: C. canimorsus, previously classified as CDC Group Dysgonic Fermenter-2 (DF-2), is a slow-growing, gram-negative bacterium that requires carbon dioxide for growth (2). This organism has been isolated from the saliva of healthy dogs and cats as a component of the normal flora; it is susceptible to many antibiotics (e.g., penicillin, amoxicillin, erythromycin, tetracycline, cefoxitin, and clindamycin). The clinical course in severe infections is marked by disseminated intravascular coagulation, with a case-fatality rate of 25% (1). Some experts recommend that persons with risk factors such as a history of asplenia, alcoholism, or hematologic malignancy receive antibiotic prophylaxis following animal bites (3). Although this investigation did not establish a specific source of infection, evidence that the patient's thumb may have been infected, coupled with his dog ownership, suggests the sepsis resulted from a cellulitis associated with exposure to his dogs.

Plague is endemic in New Mexico; four human cases were diagnosed in 1992 and four in 1991. In this case, the decision to administer plague prophylaxis to contacts was based on the presumptive, postmortem diagnosis of plague, a compatible clinical history and high antiplague serology, and the possibility of pneumonic plague.

The cause of the false-positive plague serology remains unknown. The initial testing of the patient's serum was done with positive- and negative-control serum, but retesting of the serum with fresh reagents did not confirm the initial positive result. This false-positive plague seroreactivity may have been caused by a subtle deterioration of the reagents coupled with unusual properties of the patient's serum specimens.

This report underscores the importance of confirming positive plague serologic tests, preferably with a different lot of reagents and with cultures, in patients with clinical syndromes compatible with plague but who lack other laboratory evidence (e.g., a positive plague IFA and/or culture) of plague. Laboratory confirmation of infection with Y. pestis by serologic testing or by culture can be obtained from CDC's Bacterial Zoonoses Branch, National Center for Infectious Diseases, Fort Collins, Colorado, telephone (303) 221-6453.

References

1. Job L, Hormann JT, Grigor JK, Isreal E. Dysgonic fermenter-2: a clinico-epidemiologic review. J Emerg Med 1989;7:185-92.

2. Brenner DJ, Hollis DG, Fanning GR, Weaver RE. Capnocytophaga canimorsus sp. nov. (formerly CDC group DF-2) a cause of septicemia following dog bite, and C. cynodegmi sp. nov., a cause of localized wound infection following dog bite. J Clin Microbiol 1989;27:231-5.

3. Goldstein EJC. Bite wounds and infection. Clin Infect Dis 1992;14:633-40.

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