Clinical Overview of Capnocytophaga

What to know

Capnocytophaga is a rare infection usually caused by bacteria from dog or cat bites. Symptoms start 3-5 days after exposure and can progress from mild, localized infection to a dangerous systemic infection. Capnocytophaga infections can be treated with antibiotics, but disease complications can arise quickly and potentially be fatal.

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Signs and symptoms

There are 9 species of Capnocytophaga, which can be classified into 2 main categories:

Capnocytophaga species are fastidious, slow-growing, Gram-negative bacteria.
Culture of a Capnocytophaga species. All are fastidious, slow-growing, Gram-negative bacteria.

Human-oral associated, seen more commonly in immunocompromised patients: C. gingivalis, C. granulosa, C. haemolytica, C. leadbetteri, C. ochracea, and C. Sputigena

Most reported human-oral associated Capnocytophaga infections cause:

  • Periodontal infections
  • Respiratory tract infections
  • Ocular infections

Zoonosis associated, seen more commonly in asplenic patients or those with liver disease: C. canimorsus, C. canis, and C. cynodegmi

Symptoms from zoonosis associated Capnocytophaga infections typically begin about 3 to 5 days after a dog or cat bite. The disease can progress rapidly from mild, localized infection to systemic infection, sepsis, and death.

Signs and symptoms of a Capnocytophaga infection include:

  • Blisters at the bite or scratch wound
  • Redness, swelling, draining pus, or pain at the wound
  • Fever
  • Diarrhea and/or stomach pain
  • Vomiting
  • Headache and/or confusion

Risk factors

Most Capnocytophaga infections occur in adults over 40 years of age.

People with the following medical histories comprise 60% of Capnocytophaga infections:

  • Splenectomies
  • Excessive alcohol use (regular binge or heavy drinking)
  • Cancer and cancer treatment
  • Chronic lung disease
  • Diabetes


Capnocytophaga infections are not nationally notifiable, and therefore there is no national estimate of incidence. Cases are rarely reported in the literature.

Laboratory testing and identification

Capnocytophaga species are slow-growing, Gram-negative bacteria that are difficult to grow in a laboratory setting.

Blood samples are usually used to identify the bacteria in culture, but identification can be difficult. In a California study, only approximately 1/3 of Capnocytophaga samples were correctly identified by the state public health laboratories that submitted them.

Automated blood culture systems may not identify Capnocytophaga growth because of its slow-growing nature. Some other bacteria species are very similar to Capnocytophaga, and biochemical analysis used to identify bacteria species may not be able to tell the difference.

Other more reliable methods for identifying Capnocytophaga include:

  • PCR
  • 16S rRNA gene amplification
  • Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI TOF) mass spectrometry

CDC's Special Bacteriology Reference Laboratory or your state health department laboratory can conduct these tests. To submit a sample to CDC for Capnocytophaga identification, see laboratory submission information.

All submissions to CDC must come from within the United States and must be approved by your state health department.

MicrobeNet, a CDC virtual reference laboratory, can also help identify rare pathogens like Capnocytophaga.

Treatment and recovery

Capnocytophaga is typically sensitive to routinely used antibiotics. Healthcare providers can determine the most appropriate course of treatment based on patient's history and clinical presentation.

Patients with severe Capnocytophaga infection should be treated initially with a beta-lactam-beta-lactamase combination (such as piperacillin-tazobactam) or a carbapenem (such as imipenem), pending susceptibility testing. If antibiotic susceptibilities are performed, the regimen can be adjusted accordingly. Patients with non-severe infection may be treated with oral therapy such as amoxicillin-clavulanate or clindamycin.

The infection can quickly progress, and death is due to complications from shock, disseminated intravascular coagulation (DIC), and organ failure. Capnocytophaga-associated morbidity can include sepsis, myocardial infarction, renal failure, and amputation because of DIC.

Asplenic patients have a 30 to 60 times greater risk of death from Capnocytophaga infections. These patients can advance to organ failure and death within 24 to 72 hours of onset.

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