Monthly Archives: May 2015

Dogbites: Management of Infections, A Practical Blogpost

Angry Dog

This past week was National Dogbite Prevention Week.  Every year, more than 4.5 million people in the US are bitten by dogs.  As an infectious diseases doc, I get involved only after prevention has failed: the patient is now in the ER after being mauled and I am called regarding post-bite infection prophylaxis, rabies prophylaxis, or (if the patient presents late and with infection) about appropriate antibiotic treatment for an infected bite. This post will detail my general approach to any bitewound and specifically focus on management of dogbites.

So, first let’s establish the legal rules of engagement: Don’t take anything stated here as medical advice and please consult a doctor if you have been bitten by any animal (including human). The internet is an inadequate source of medical information to treat yourself, family or friends.

General Approach for any Bitewounds, History:

When evaluating patients who have been bitten by an animal, it is vital to obtain detailed history of the attack. Such information is not only important to guide evaluation and treatment of the patient, but also is of legal importance. An animal bite case may proceed to a lawsuit for personal injury. And animal control may weigh whether the involved animal is a nuisance to be seized and destroyed.

Key aspects of the history of attack to be obtained:

Type of animal
Ownership of animal
Rabies vaccination history (of the animal and the bite victim)
Attack provoked or unprovoked
Health of animal: Is it in custody?

I’m not sure this mnemonic, TORAH, will make sense for others, but it has worked for me.

The provider also needs to obtain typical medical history of the patient-victim.    I would note the special importance of the following items in the history, however:

Medications with potential drug-drug interactions

Calcium supplements
Ca or Mg containing antacids

Medical problems increasing risk of infectious complications:

Liver disease
Aplenia/ hyposplenia
Steroid use


A focused examination of a patient who has been bitten by an animal should not overlook the possibility of occult injury. A thorough search should be conducted to assure no other wounds are present that escaped the patient’s attention.

Wounds should be accurately described or diagramed in the medical record. Special attention should be given to determine if there is neuromuscular compromise. Joint range of motion and tendon function should be assessed. Wounds should be probed. Even wounds that appear superficial may penetrate deep to bone.

Assessing for Bitewound Infection:
In the setting of a patient presenting late after the bite, careful assessment for infection should be performed including noting presence of purulent discharge, surrounding cellulitis, lymphangitis, and proximal lymphadenopathy. Wound cultures should be obtained from wounds that are clearly infected and from significant bite wounds due to animals other than cats and dogs. Do NOT culture dog or cat bite wounds that clinically do not appear infected. (Culture results will not inform decision making regarding choice of antibiotics in this setting.)
Imaging should be obtained on bitewounds in the following scenarios:

– Fracture is suspected
– Concern for foreign body (eg, embedded tooth)
– Potential for bone or joint involvement
Wound Management:
Wounds should be cleaned with normal saline. A variety of wound irrigation systems are commercially available, though at its simplest, an 18 or 19 gauge needle on a 35 cc syringe will do the trick. A splashguard protects from bloody spray. Use 100- 200 cc of saline for every 5 cm of wound length. Devitalized tissue should be debrided.

Avoid suturing bite wounds in the following settings:

Bites to distal extremities (especially hands)
Bites of older age
> 6 – 12 hours on extremities
> 12 – 24 hours on the face
Human bite wounds

Monofilament suture is preferred over braided suture due to less infectious risk with the former. Subcutaneous sutures should be used sparingly.

Infectious prophylaxis:
Bitewounds, by definition, are tetanus prone wounds and tetanus prophylaxis needs to be considered. If the patient has received the three doses of the primary tetanus series and has received tetanus toxoid (Td) in the preceding 5 years, no tetanus prophylaxis is indicated. If it has been greater than 5 years since the most recent Td immunization, then Td should be administered. If the patient has not completed the three doses of the primary series (or if unknown), then the patient should receive Td (as well as complete the 3 dose series) and receive tetanus immune globulin.

Rabies prophylaxis also needs to be assessed following a dog bite (as well as any mammalian bite). If in doubt, contact your state or local public health authorities for up to date guidance. If the attacking dog is suspected to be rabid based on behavior or if the attack was particularly ferocious with significant trauma and/or involvement of the head or neck, then Human Rabies Immune Globulin (HRIG) and rabies vaccine should be administered per standard protocol.
If there is low suspicion the dog is rabid and the animal is in custody, then it can be observed for ten days, watching for signs or symptoms of rabies. If no rabies in the 10 day time frame then the dogbite victim does not need rabies prophylaxis. If the animal develops symptoms, then Human Rabies Immune Globulin (HRIG) and rabies vaccine should be administered. If an attacking dog escaped and rabies determination cannot be made, then a phone call to public health authorities for guidance is reasonable. In most jurisdictions with ongoing epizootic rabies, rabies prophylaxis would be indicated given the fatal nature of human rabies infection.

Bacterial Infection
It is estimated that 5% of dogbites become infected. This is in contrast to catbites, where ~80% are estimated to become infected. Antibiotic prophylaxis for dogbites, should be considered based on the host and the severity of the mauling. If the patient has diabetes, immunosuppression, hyposplenism, or chronic immunosuppressive medications, antibiotic prophylaxis would be prudent. Additionally, even in the normal host, it is reasonable to prophylaxis a patient with extensive injuries.

Dogbite infections (like other bitewound infections) are polymicrobial. In the case of dogbites, the more important pathogens include:

Capnocytophaga canimorsus
Pasteurella canis
Staphylococcus aureus
Oral Streptococci
Neisseria spp.
Corynebacterium spp.
Moraxella spp.
Enterococcus spp.
Bacillus spp.
Fusobacterium spp.
Porphyromonas spp.
Prevotella spp.
Propionibacterium spp.
Bacteroides spp.

Capnocytophaga canimorsus is of special importance in the asplenic or hyposplenic patient where it can cause overwhelming sepsis. Classically an eschar is present at the site of inoculation or bite. Disseminated intravascular coagulation is typical. Several years ago, I was involved in a case of a hospitalized patient with Capnocytophaga infection. He was a middle aged cirrhotic patient. His clinical course was impressive with overwhelming septic shock, renal and hepatic failure, purpura fulminans, peripheral dry gangrene with auto-amputation of the nose, ears, feet, and hands. He had an inexorable progression despite appropriate antibiotics administered in a timely manner from the point of his initial presentation for medical care. It was a humbling experience, demonstrating how futile our medical interventions can be.

Pasteurella species are an important cause of animal bite infections. P. canis occurs in dogs. P. multocida is typical in cats (including interestingly, not only housecats, but also big cats). It is relevant to consider these pathogens, because of their spectrum of antibiotic resistance. The species are resistant to cephalexin, dicloxacillin, clindamycin, and variably resistant to erythromycin.

Staphylococcus intermedius is an important canine zoonotic pathogen that can be acquired via bite. Medical microbiology labs may incorrectly identify the pathogen as Staph aureus, because S. intermedius is also coagulase positive. In contrast to S. aureus, however, S. intermedius has beta-galactosidase activity and fails to produce acetoin. Automated microbiology systems may incorrectly identify S. intermedius as methicillin resistant Staph aureus (MRSA). An astute clinician may need to speak to the microbiologist ’working up’ the specimen in order to pursue molecular techniques of identification in the setting of an appropriate canine exposure.

For empiric coverage of dog bite infections, oral amoxicillin-clavulanate or intravenous ampicillin-sulbactam are first line antibiotic options. In the penicillin allergic patient, clindamycin plus a flouroquinolone can be considered. In children, where a quinolone would be contraindicated, clindamycin plus trimethoprim-sulfamethoxazole is an option. Decisions regarding choice of antibiotics should always be informed by local resistance patterns, patient factors, and the patient’s specific culture results.

And for future prevention, the patient should be educated regarding dog bite prevention.


Abrahamian, FM & EJC Goldstein. 2011. Microbiology of animal bite wound infections. Clin Microbiol Rev 24(2): 231- 46.

Cummings, P. 1994. Antibiotics to prevent infection in patients with dog bite wounds: A meta analysis of randomized trials. Ann Emerg Med 23: 535- 40.

Gaastra, W & LJ Lipman. 2010. Capnocytophaga canimorsus. Vet Microbiol 140(3-4): 339-46.

Goldstein, EJC, DM Citron, and GA Richwald. 1988. Lack of in vitro efficacy of oral forms of certain cephalosporins, erythromycin, and oxacillin against Pasteurella multocida. Antimicrob Agents Chemother 32: 213-5.

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

Holm, M and A Tärnvik. 2000. Hospitalization due to Pasteurella multocida-infected animal bite wounds: Correlation with inadequate primary antibiotic medication. Scand J Infect Dis 32: 181- 3.

Quinn, PJ, ME Carter, B Markey, And GR Carter. 1999. Clinical Veterinary Microbiology Mosby, New York.

Sacks, JJ, M Kresnow, and B Houston. 1996. Dog bites: How big a problem? Inj Prev 2: 52- 4.

Stevens, DL, et al. 2014. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis doi: 10.1093/cid/ciu296

Talan, DA, DM Citron, FM Abrahamian, et al. 1999. Bacteriologic analysis of infected dog and cat bites. NEJM 340: 85-92.

Talan, DA, et al. 1989. Staphylococcus intermedius: clinical presentation of a new human dog bite pathogen. Ann Emerg Med 18: 410- 3.

Talan, DA, et al. 1989. Staphylococcus intermedius in canine gingiva and canine-inflicted human wound infections: Laboratory characterization of a newly recognized zoonotic pathogen. J Clin Microbiol 27: 78- 81.

Another Month, Another Zoonosis: Plague in Colorado

This month, the Morbidity Mortality Weekly Report and the New England Journal of Medicine reported a cluster of pneumonic plague that occurred in Colorado during the summer of 2014.

Yersinia pestis on blood agar plate (left) and chocolate agar plate (right). Source: CDC Public Health Image Library. Common Domain.

Yersinia pestis on blood agar plate (left) and chocolate agar plate (right).
Source: CDC Public Health Image Library.
Common Domain.

For a review of plague and its forms (bubonic, septicemic, and pneumonic), please refer to the CDC webpage.

There are several points to be made about this outbreak.

(1) This outbreak is the largest pneumonic plague epidemic in the United States in 90 years. The index case was a dog. The dog’s owner, two veterinary employees, and a companion of the dog’s owner became ill. Pneumonic plague is rare. Of reported cases of plague in the United states, over 80% have been bubonic. It’s a lucky thing that pneumonic plague is rare because it is the most dangerous form of the disease from an epidemiologic perspective. Patients with pneumonic plague can spread the bacterial infection person-to-person via droplets (produced with coughing for example). This can lead to rapid amplification of case numbers.

(2) The automated blood culture system misidentified the bacteria cultured from the index human patient. Rather than correctly identifying it as Yersinia pestis, the machine misidentified it as Pseudomonas luteola. This resulted in a delay of diagnosis. Errors in the identification of Y. pestis by automated blood culture systems have previously been described.  This highlights the risk of relying solely on sophisticated equipment to identify pathogens without the ability to perform traditional microbiological and biochemical methods of bacterial identification.

(3) Plague is enzootic to the American Southwest and West.  (See map.)

The diagnosis of plague needs to be considered in the differential of patients who present with lymphadenitis, undifferentiated septicemia, and community acquired pneumonia in the context of exposure to ill animals. The risk of transmission from pets is greatest with cats. Dogs are a rare source of plague in humans.

(4) Y. pestis is a potential agent of bioterrorism, listed as a category A agent by the CDC. As such, plague may need to be considered in the differential anytime there is an unusual cluster of severe illness or progressive pneumonia.

(5) This case again highlights the importance of communication across health specialties including veterinary medicine, human medicine, public health, and ecology / wildlife biology.



Foster, CL, et al. 2015. Sick as a dog. NEJM 372(19): 1845- 50.

Gage, KL, et al. 2000. Cases of cat-associated human plague in the Western US, 1977- 1998. Clin Infect Dis 30:893- 900.

Gould, LH, et al. 2008. Dog-associated risk factors for human plague.  Zoonoses Public Health 55:448- 54.

Kool, JL. 2005. Risk of person-to-person transmission of pneumonic plague. Clin Infect Dis 40:1166- 72.

Kugeler, KJ, et al. 2015. Epidemiology of human plague in the United States, 1900-2012. Emerg Infect Dis 21:16- 22.

Nichols, MC, et al. 2014. Yersinia pestis infection in dogs: 62 cases (2003–2011). J Am Vet Med Assoc 244:1176- 80.

Runfola, JK, et al. 2015. Outbreak of Human Pneumonic Plague with Dog-to-Human and Possible Human-to-Human Transmission- Colorado, June–July 2014. MMWR 64(16): 429- 34.

Wang, H, et al. 2011. A dog-associated primary pneumonic plague in Qinghai Province, China. Clin Infect Dis 52:185- 90.