Mammalian Bites: ED presentations, evaluation, and management
- Oct 12th, 2020
- Erin Rizzo
Authors: Erin Rizzo, MD (EM Resident Physician, University of Kentucky) and Jaryd Zummer, MD (EM Attending Physician, University of Kentucky) // Reviewed by: Alex Koyfman, MD (@EMHighAK); Brit Long, MD (@long_brit); Jamie Santistevan, MD
A 34-year-old female with no significant past medical history presents to the Emergency Department reporting she was bitten by a large dog. She was on a run immediately prior to arrival and came across a dog without a collar. She reached down to pet the dog when he attacked her right hand and arm. She has a blood-soaked towel wrapped around the wounds. She is not on any blood thinners. Her vital signs are all normal.
How should this patient be evaluated and managed?
Epidemiology and Background
It is estimated the half of Americans will be bitten by either an animal or another human at some point in their life(1). The true incidence of mammalian bites is unknown, however, it is estimated that 2 million Americans are bitten every year and that about half of these come to the Emergency Department(2). These account for 5% of traumatic wounds seen in the ED(3), and over 10,000 patients require admission yearly(4). It is estimated that these patients cost the healthcare system $850 million yearly(2). Dog bites account for approximately 90% of animal bites presenting to the Emergency Department and are most common in male children. Cat bites make up about 10% and are most common in adult women(4).
Management in the Emergency Department
If the patient is hemodynamically unstable, they should be treated as any major penetrating trauma would be treated. Bleeding should be controlled with direct pressure or a tourniquet as needed. Local hemostatic agents or antifibrinolytics can be considered. IV access should be obtained and the patient should be resuscitated(5). In children, who are often bitten on the neck, head and face, the patient’s airway as well as other underlying structures should be thoroughly assessed. The wounds should then be thoroughly cleaned with soap, water, and povidone iodine or other antiseptic solution(4). Copious irrigation at high pressure has been shown to markedly decrease the concentration of bacteria in the bite wounds(6). Debris should be removed and the wound should be thoroughly examined(4).
It is important to determine the age and mechanism of the injury, the extent of the wound, and the cosmetic impact of the wound. The age of the wound is important when deciding if the wound can be closed or should be left open to heal by secondary intention. Exactly how the bite occurred, including if it was provoked or unprovoked, and the type of animal as well as its vaccination status is important when considering rabies prophylaxis. The wound should be thoroughly explored which may require local anesthetics, nerve blocks, or tourniquets. The base of the wound should be identified, and if there is any concern for foreign body, fracture, or joint disruption, X-ray is recommended. All tendons, nerves, and vessels should be evaluated. If the wound is in a cosmetically sensitive area, such as at the vermilion border of the lip, on the eyelid, nose, or ears, or if it is a large laceration to the face consultation with a surgical specialist should be considered(7).
Common recommendations for which wounds are left open to heal by secondary intention include(4, 6, 8, 9):
- Cat bites
- Human bites
- Any bites to the hands or feet
- Any bite >12 hours old (>24 hours old on the face)
- Crush injuries
- Puncture bites
- Bites in an immunocompromised patient
- Bites in patients with venous stasis
While most experts agree on the above recommendations for leaving bite wounds open, there is an increasing body of evidence to suggest certain lower risk wounds can be primarily closed without adding significant risk of infection. One study comparing infection rates of dog bites who presented within 8 hours of the incident and underwent primary closure to those that were left to heal by secondary intent showed no significant difference in infection rates. All of these patients were given antibiotics(10). A Cochrane review comparing primary closure of dog bites with no closure (878 patients) and comparing primary closure with delayed closure (120 patients) found no significant difference in the rates of infection(8). Smaller studies have shown that primary closure may improve cosmesis, but more robust studies are needed to validate this fact(8, 11). Patient’s wishes, comorbidities, compliance, and the extent and location of the wound should be carefully considered. After discussion of the risks and benefits with the patient, joint decision-making should be employed.
Bites to the face can generally be closed. The face is not only of cosmetic importance but has a lower risk of infection, which is thought to be related to the increased vascularity as well as lack of dependent edema(12). In a study of 87 children who received primary closure and prophylactic antibiotics after a dog bite to the face, none developed infection(13). No bite wound should be closed with glue and all should be single layered closures to reduce the risk of infection(4,14). Large gaping wounds should be approximated. All bite wounds should be thoroughly debrided, irrigated, dressed, and then examined daily for signs of infection. The median time to onset of symptoms of infection is about 12 hours in cat bites and 24 hours in dog bites(15). If preferred, these patients can return for delayed primary closure if there are no signs of infection after 2 to 3 days(4).
Surgical consultation is generally indicated in the following circumstances(9):
- Complex facial lacerations
- Deep wounds that penetrate bone, tendon, joints, or other structures
- Wounds that cause neurovascular compromise
- Deep infection (septic arthritis, osteomyelitis, tenosynovitis, etc.)
- Infection of the hands or face
- Infection with neurovascular compromise
- Infection with foreign body
- Infection in immunocompromised patients
- Concern for necrotizing soft tissue infection (rapidly progressive infection, crepitus)
- Persistent infection after antibiotics
- Clenched fist wounds (fight bites)
- Significant avulsion or amputation
- Bites with delayed presentation, extensive infection, or systemic symptoms
Strongest evidence for antibiotic prophylaxis are for bites to the hand. There is also some evidence that suggests using prophylactic antibiotics for clinically significant human bites. There is not strong evidence, however, supporting prophylaxis in bites from domestic animals that do not involve the distal extremities(8, 16). If the decision is made to give antibiotics, time to administration has been associated with a decrease in complications, so strongly consider giving the first dose in the Emergency Department(2, 17). One study of 674 patients found a statistically significant reduction in the rate of infection after human bites and bites to the hand that were treated with antibiotics, with a number needed to treat of 4. There was no reduction in the rate of infection after other dog or cat bites were treated with antibiotics(16). Wound type did not appear to contribute (puncture vs. laceration), however other factors like wound location, blood supply, and comorbidities may significantly influence the benefit of antibiotics(16). While some experts prefer antibiotics in all cat bites as well as human bites, the evidence to support this practice is likely due to a selection bias. Because most cat bites are small and not immediately concerning, they often do not present for medical evaluation unless they become infected. Dog bites are much more likely to present to the emergency department immediately because the wounds are often more damaging with avulsions, large lacerations, and crushed tissue being common(8).
Most studies suggest prophylactic antibiotics be given in the following circumstances(10, 12, 17):
- Being primarily closed or require surgical repair
- On the hands, face, or genitals
- In close proximity to bones or joints
- Patient with underlying venous or lymphatic compromise
- Immunocompromised patient (including diabetes)
- Deep punctures or deep lacerations
- Associated crush injuries
If the above criteria are met, the patient should be empirically treated for Pasteurella, Strep, Staph, and anaerobes. Although Pasteurella species is the most frequent isolate from animal bites (found in 50% of dog bites and 75% of cat bites), both dog and cat bites usually have up to 5 bacterial isolates per culture(15). The oral options below should be used prophylactically or if the patient already has an infection. If the patient has systemic toxicity, deep infection, rapid progression of infection, progression after 48 hours of oral antibiotics, inability to tolerate PO, or wounds near an indwelling catheter, parenteral regimens below should be used(10, 12).
- Oral options:
- Amoxicillin-clavulanate 875 mg BID for 5-7 days OR
- Clindamycin 450 mg TID for seven days PLUS
- Ciprofloxacin 500 mg BID for 7 days OR
- Trimethoprim sulfamethoxazole double-strength BID
- IV options:
- Ampicillin/sulbactam 3g QID daily OR
- Cefoxitin 1g TID OR
- Piperacillin/tazobactam 4.5g TID OR
- Ceftriaxone 1g once + Metronidazole 500mg TID
- Clindamycin 600 mg TID PLUS
- Trimethoprim-sulfamethoxazole 5mg/kg BID OR
- Ciprofloxacin 400mg BID
There are two common types of human bite injuries: clenched fist injuries and frank bites. Clenched fist injuries or “fight bites” are most common in adolescent and adults males. These patients most commonly present with lacerations over the third and fourth dorsal MCP of their dominant hand. These are at high risk for deep tendon laceration, extensor tenosynovitis, osteomyelitis, septic arthritis, and other complications. They require antibiotics and hand-surgery evaluation. A high index of suspicion must be kept when encountering patient with dorsal hand lacerations or fractures as they may represent human bite injuries(9, 10, 18, 19). Frank bites are most commonly seen in young children and adult women. They should all be screened for abuse. In both types of bites up to 25% of patients present greater than 48 hours after the injury and many do not present until complications, like infection, are present(4).
Rabies prophylaxis is indicated in the United States for bites from bats, monkeys, skunks, raccoons, and foxes, as well as domestic animals that cannot be quarantined. If the animal’s vaccination status is unknown or if the animal is not captured, public health officials should be contacted to discuss risk of rabies in the area and the need for prophylaxis(20). The CDC recommends that rabies prophylaxis be postponed if animals can be tested or quarantined for 10 days(20). If during those 10 days the animal’s behavior becomes wild or erratic, rabies prophylaxis should be started and the animal’s brain should be biopsied. If the biopsy results are negative, prophylaxis can be discontinued. This can usually be organized through the local health department and providers should familiarize themselves with how this is handled in the area in which they work. Small rodents like squirrels, gerbils, hamsters, chipmunks, rats, and mice have not been shown to transmit rabies to humans so prophylaxis is not indicated(21).
Between 1980 and 2015, 87% of rabies cases in the United States were from bats. Many patients did not recall being bitten by bats, likely because their teeth are very sharp and small. If a bat is found in the same room with a child, intoxicated adult, or mentally disabled adult rabies prophylaxis should be administered. In adults who are not certain whether or not they were bitten, including those who are sleeping in the same room as a discovered bat, rabies prophylaxis should be given. There were 31 reported cases of rabies in the United States from 2003 to 2016. Eleven were from dogs, however all of these dog bites were acquired in a foreign country. In third-world countries, dogs cause 90% of rabies cases. About 70 dogs are diagnosed with rabies in the United States every year, most commonly near the Mexico border, however there are sometimes other local outbreaks(21).
Rabies prophylaxis includes rabies immunoglobulin (20 IU/kg) and rabies vaccination. The immunoglobulin should be administered on the day of presentation inside or as close to the wound as possible. Subcutaneous and intramuscular immunoglobulin have not been shown to be as effective. If there is extra immunoglobulin that cannot be injected at the site of the wound, it should be administered at a site distant from the vaccine. The patient also needs rabies vaccination on the day of presentation as well as on days 3, 7, and 14(21). The Indian National Guidelines on Rabies Prophylaxis recommends against closing wounds if the patient is receiving rabies vaccination or at least delaying closure for a few hours to increase diffusion of the immunoglobulin into the tissues(22). Because the incubation period of rabies is 1-3 months, prophylaxis should be administered even if the initial presentation is delayed. If a patient presents with symptoms, rabies is almost always fatal(23).
HIV, Hepatitis B or C, and herpes simplex virus transmission from human bites is very rare. There have been 9 cases in the world of HIV transmission through a human bite. Two were from untrained first responders who put their fingers in the mouth of a seizing patient and the other seven were from fight bites. In all cases the HIV positive patient had significant bleeding in their mouth and the person punching them had a significant break in the skin of their hand(24).
Monkey bites should be treated with 1g of PO Valacyclovir TID for 14 days or 800mg of PO Acyclovir 5 times daily for 14 days. This is because monkeys are carriers of Cercopithecine herpesvirus 1 (also known as Herpesvirus simiae or B virus) which can cause fatal encephalitis if not treated appropriately(14). Squirrel, rabbit, guinea pig, rodent, and other small animal bites should be treated like cat bites(4).
Pearls and Pitfalls
- Clenched fist injuries (“fight bites”) are high risk injuries that require antibiotics and hand surgery consultation.
- Augmentin is the oral antibiotic of choice for both prophylaxis and treatment of infected mammalian bites.
- In the United States, bats are the most common cause of rabies while in other countries dogs cause most cases. Patients at risk, including children and intoxicated or mentally disabled adults found in the same room as a bat, should get both rabies immunoglobulin and vaccination.
- HIV transmission from bites is very rare however if a patient has a significant wound to their hand after a bite from an HIV positive patient, especially one with a lot of bleeding in the mouth, PEP should be discussed.
References / Further Reading
- Griego RD, Rosen T, Orengo IF, Wolf JE. Dog, cat, and human bites: a review. J Am Acad Dermatol. 1995;33(6):1019-1029. doi:10.1016/0190-9622(95)90296-1
- Doty, Christopher. Mammalian Bites. EM:Rap. August 2010.
- Swaminathan, Anand. Dog Bite Myths. EM:Rap. Episode 150. March 2014
- Baddour LM, Harper M. Animal Bites (dogs, cats, and other animals): Evaluation and management. January 2020.
- Colwell C. Initial Management of Moderate to Severe Hemorrhage in the Adult Trauma Patient. April 2020.
- Fleisher GR. The management of bite wounds. N Engl J Med 1999; 340: 138.
- Brancato JC. Minor Wound Preparation and Irrigation. December 2019.
- Bhaumik S, Kirubakaran R, Chaudhuri S. Primary closure versus delayed or no closure for traumatic wounds due to mammalian bite. Cochrane Database Syst Rev. 2019 Dec 6;12(12)
- Kannikeswaran N, Kamat D. Mammalian bites. Clin Pediatr (Phila) 2009; 48: 145).
- Medeiros I and Saconato H. Antibiotic Prophylaxis for Mammalian Bites. Cochrane Database Systematic Rev. 2001; (2): CD001738.
- Eppley BL, Schleich AR. Facial dog bite injuries in children: treatment and outcome assessment. J Craniofac Surg. 2013;24(2):384-386. doi:10.1097/SCS.0b013e31827fee33
- Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America [published correction appears in Clin Infect Dis. 2015 May 1;60(9):1448.
- Wu PS, Beres A, Tashjian DB, Moriarty KP. Primary repair of facial dog bite injuries in children. Pediatr Emerg Care. 2011;27(9):801-803. doi:10.1097/PEC.0b013e31822c1112
- Dendle C, Looke D. Management of mammalian bites. Aust Fam Physician. 2009;38(11):868-874.
- Talan DA, Citron DM, Abrahamian FM, Moran GJ, Goldstein EJ. Bacteriologic analysis of infected dog and cat bites. Emergency Medicine Animal Bite Infection Study Group. N Engl J Med. 1999 Jan 14;340(2):85-92
- Turner TW. Evidence-based emergency medicine/systematic review abstract. Do mammalian bites require antibiotic prophylaxis? Ann Emerg Med. 2004;44(3):274-276. doi:10.1016/j.annemergmed.2004.05.025
- Cummings P. Antibiotics to prevent infection in patients with dog bite wounds: a meta-analysis of randomized trials. Ann Emerg Med. 1994;23(3):535–540
- Baddour LM, Harper M. Human Bites: Evaluation and management. July 2019.
- Talan DA, Abrahamian FM, Moran GJ, et al. Clinical presentation and bacteriologic analysis of infected human bites in patients presenting to emergency departments. Clin Infect Dis. 2003;37(11):1481-1489. doi:10.1086/379331
- Brown, Catherine. When to Use Rabies Prophylaxis. UpToDate, July 18, 2018.
- Swaminathan and Hope in Herbert. Rabies. EM:Rap 18(12): 11-2. 2018
- Gupta, Naveen. National Guidelines for Rabies Prophylaxis. National Centre for Disease Control.
- “Rabies.” World Health Organization.
- Cresswell FV, Ellis J, Hartley J, Sabin CA, Orkin C, Churchill DR. A systematic review of risk of HIV transmission through biting or spitting: implications for policy. HIV Med. 2018;1–9.