BAD BITES
| MAMMALIAN BITE MANAGEMENT —Ellen J. Weber, MD, Professor of Clinical Medicine, University of California, San Francisco, School of Medicine |
| Dog bites: low risk for infection (5%-10%) unless hand involved (13%-30%); well vascularized areas at low risk for infection; most wounds that do become infected usually easily treated with first-generation cephalosporin on outpatient basis; only 1% of patients require hospitalization (usually for cosmetic surgery, mostly children bitten on face); create superficial, wide, gaping wounds; bites usually penetrate to muscle, not bone, tendon, or joints; easy to clean, debride, irrigate, and suture; size of wound and dog’s teeth usually bring victims into emergency department (ED) quickly; cultures yield (on average) 5 different organisms per wound; Staphylococcus and Streptococcus still most common; species of Pasteurella, if found, usually not highly virulent (Pasteurella canis and Pasteurella stomatis); in contrast, 75% of cat bites have Pasteurella, mostly pathogenic species, eg, Pasteurella multocida; 1986 study showed most infected dog bite wounds healed with cephalexin (Keflex), suggesting that in multiorganism infections, only predominant organisms need be treated |
 | Capnocytophaga canimorsus (dysgonic fermenter-2; DF-2): gram-negative facultatively anaerobic rod that has caused sepsis in small number of people; can be fatal; 75% of victims immunosuppressed in unusual way (ie, not HIV, but have no spleen, have lung disease, taking steroids, or alcoholic); 25% have no apparent underlying illness; associated with contact with dog or cat; causes generalized sepsis with hypotension, petechiae, purpura, and adrenal hemorrhage; ≈25% mortality; susceptible to most drugs used for sepsis of unknown etiology and for prophylaxis of wounds (prophylaxis indicated in any immunosuppressed patient with dog bite); very slow growing (warn laboratory not to throw out blood culture too soon); may see organism in peripheral blood smear at time of presentation or in Gram’s stain of blood culture before macroscopic growth |
| Summary: dog bites low risk except for hands; Pasteurella multocida not major threat; patients with infections can generally be treated as outpatients; consider DF-2 in patients with risk factors |
| Cat bites: infection rate 30% to 50%; greater morbidity in local and systemic infection; 6% of patients hospitalized (almost all for infection); higher risk for infection because bites are puncture wounds; cats have sharp teeth that often penetrate to bone, tendon, and joint; cat biting owner on hand most common; patients generally delay treatment when bitten by own cat (present only if bite becomes infected); 70% of cats have Pasteurella in their saliva (50% of dogs); when Pasteurella present, likely to be sole pathogen; may cause early cellulitis and known to cause osteomyelitis, septic arthritis, endocarditis, pyelonephritis, and meningitis; Pasteurella not sensitive to erythromycin, dicloxacillin, or clindamycin, but very sensitive to penicillin, tetracycline, quinolones, second- and third-generation cephalosporins, and azithromycin; also treat Staphylococcus and Streptococcus |
| Rodents: wound infection rate 2%; bites usually cause local cellulitis that can be easily treated with first-generation cephalosporin or dicloxacillin; no cases of rodent transmission of rabies to humans in United States (bats are not rodents and have high risk for rabies) |
| Ferrets: third most common pet in United States; members of skunk and weasel family; outlawed in California and Hawaii; 500,000 pet ferrets in California; known for sudden, unprovoked, disfiguring attacks on infants (feed on suckling animals in wild); cage not protective (ferrets known to escape, hide for days, then attack); can carry and transmit rabies, although no cases in United States (rabies vaccine available for ferrets, even in states where ferrets outlawed) |
| Clenched-fist injury: high risk; laceration over third, fourth, or fifth metacarpophalangeal joint; usually ragged; often penetrates through joint and rips tendon; more bacteria present due to force involved; opening hand closes wound with bacteria inside; ≤50% of cases present already infected (these patients often drunk and awaken to swollen hand); associated underlying injuries in ≈25% of cases; 50% of patients have complications, eg, osteomyelitis, septic arthritis, residual joint stiffness, necrosed extensor tendons, amputations; almost all complications in people who present late (primary reason clenched-fist injuries problematic) |
| Simple bites: eg, child vs child in playground setting; risk for infection no different from that of any other laceration |
| Oral wounds: eg, falling on face and injuring oral mucosa; 0% to 10% infection rate (deep and large); mucocutaneous wounds have ≈30% risk for infection |
| Microbiology: studied most in clenched-fist injuries; Staphylococcus and Streptococcus most common; Eikenella corrodens unusual infection caused by dental plaque (found in ≈25% of clenched-fist injuries); Streptococcus uses up O2 , then Eikenella takes over anaerobic environment; wounds with Eikenella tend to do worse; Eikenella resistant to first- generation cephalosporins and dicloxacillin, but sensitive to penicillin, second- and third-generation cephalosporins, tetracycline, and fluoroquinolones; Pasteurella sensitive to azithromycin but Eikenella is not; no controlled studies on any of these antibiotics in last 15 yr |
| Management: since data poor, follow general principles of wound care; for high-risk wounds, do not suture but give prophylactic antibiotics; low-risk wounds may be sutured, and prophylactic antibiotics not needed |
| High-risk wounds: locations—hand, wrist, foot, joints; type—cat and human bites; through-and-through lacerations; puncture wounds; extensive crush wounds; dirty wounds; old wounds; high-risk patients—elderly; smokers; immunosuppressed; diabetics; patients taking steroids |
| Low-risk wounds: rodent; dog; location on scalp, face, mucosa, well vascularized areas; clean large wounds; early presentation |
| Prophylactic antibiotics (study data): dog bites—antibiotics decrease risk for infection by ≈50%, but risk small to begin with, so prophylaxis not cost-effective; with hand bites, need to treat only 10 patients to prevent one infection, so prophylaxis cost-effective; suture most dog bites, but avoid suturing hand bites because of high risk for infection; cat bites— prophylaxis indicated to cover Pasteurella, staphylococci, and streptococci |
| Clenched-fist injuries: x-ray indicated; anesthetize and irrigate wound and explore in bloodless field, looking for deep tissue damage; consult hand surgeon; do not suture; prophylactic antibiotics indicated (cover staphylococci, streptococci, and Eikenella); admit patients with infection, deep structure injury, bone involvement, foreign body, or if patient unreliable, has poor health status, or if wound >24 hr old |
| Rabies: vaccine costs $1500 per series; at least 25% of doses unnecessary, yet people still dying from this disease; in United States, human rabies rare (2-3 cases annually); dog and cat rabies uncommon (no cases in ≈10 yr; only dogs known to transmit rabies in United States are dog/coyote mix at Mexican border); wild animals source of infection in United States, main vectors being raccoons, skunks, foxes, and bats |
| Epidemiology: rabies found in specific terrestrial reservoirs in specific areas of country; each type of animal and area has own variant of rabies virus (secreted in saliva of biting animal); animal usually dies within 3 days of secreting virus in saliva; most animals look sick at time they transmit illness; usually transmitted by bite; virus replicates in skeletal muscle, gets into nerve endings, and travels to spinal ganglion; 5% to 60% of people who are attacked by rabid animal develop rabies; disease fatal |
| Risk: low risk if patient bitten by domestic animal; observe animal for 10 days; if animal becomes ill, give rabies prophylaxis; if animal acting abnormally or seems ill to begin with, sacrifice immediately and treat victim according to test results; if wild animal captured, sacrifice and treat patient according to test results; treat immediately if patient bitten by wild animal in area endemic for rabies; prophylaxis indicated if animal not captured and species high-risk; if low-risk species, do not treat; if uncertain, talk to public health department; high-risk animals are skunks, raccoons, foxes, bats, dogs at Texas/Mexico border, wild carnivores in endemic areas; low-risk animals are dogs, cats, rodents, livestock; uncertain about woodchucks in eastern states and domestic animal that has free range in area endemic for rabies (consult public health department) |
| Bats: 50% of people who died from rabies had known exposure to bats, and of these 20 people, only 3 knew they had been bitten by bat; Centers for Disease Control and Prevention (CDC) recommends treatment if bite cannot be ruled out |
| Prevention and precautions: cleansing wound with soap and water in <3 hr prevents rabies; must give passive and active immunity ; give human rabies immune globulin (HRIG; passive immunity) around site of wound (as much as possible), give remaining amount intramuscularly (IM) in same limb; give first dose of human diploid cell vaccine (HDCV; active immunity) on same day, then 4 subsequent doses; give vaccine in deltoid, not in gluteal region (antibodies will not be created in fat cells); do not give HRIG and HDCV in same syringe or same arm; no contraindications |
| SNAKE BITES —Robert S. Hoffman, MD, Associate Professor of Emergency Medicine and Medicine, New York University School of Medicine, New York City |
| Snakes: hibernate during cold weather; most bites occur during warm weather; only 2 categories of poisonous snakes in United States, crotalids, ie, pit vipers (rattlesnakes, cottonmouths, water moccasins, and copperheads) and elapids (coral snakes) |
| Pit vipers: have triangular-shaped head with pit that houses heat-sensing organ; vertical elliptical pupil; rattlesnakes have rattle; cotton mouth has mouth that looks like cotton; fangs are specialized teeth, either hollow or with groove that allows venom to flow down them; venom gland located above fang and contracts reflexively or intentionally, injecting venom into victim |
| Venom: all venom about same, whether in snakes, spiders, or sea creatures; designed to immobilize and kill prey and to start digestive process; contains low molecular weight peptides that break down muscle, destroy cell integrity, and trigger coagulation cascade |
| Factors determinging degree of envenomation: how recently snake has eaten; age of snake (adult or baby; adult snake can regulate delivery of venom); location of bite (better to be bitten on extremity than on neck or head); age, size, and health of victim |
| Field first aid: elevation of bitten extremity contraindicated; because venom spreads through lymphatic spaces, elevation increases delivery of venom centrally; ice impedes movement of venom, but victims, due to their lack of knowledge, usually add freezing injury to already compromised tissue; incision and suction destroys tissue and does not extract venom; capture of snake contraindicated (venomous snakebites all managed same way, so capture poses unnecessary risk); placing tourniquet contraindicated; data not strong to support or refute use of Sawyer extractor, but downside negligible; calm patient as much as possible; remove watches, jewelry, and other articles that might cause constriction as swelling proceeds; immobilize extremity in dependent fashion; splint extremity as if patient had bony injury (to prevent muscle contraction which spreads venom); mark leading edge of swelling and note time; apply loose-fitting lymphatic constrictor while waiting to go to hospital (leaves indentations similar to those left from wearing socks) |
| Dry bites: in 25% to 33% of documented snakebites, no venom injected, ie, no edema, swelling, bruising, bleeding, or systemic injury; thus, no emergency in significant minority of people bitten (observe for 5 to 7 hr before making that judgment) |
| Signs and symptoms: presence of 1, 2, or 3 fang marks (multiple bites can be present); distance between fang marks approximately equal to length of fang; if >1 inch apart, probably not dealing with snakebite; mild envenomation—defined as local swelling or local bruising near bite site; moderate envenomation—if swelling passes major joint (eg, bitten on hand and swelling above wrist); severe envenomation—if extremity swells >12 inch distal from bite injury or swells beyond second big joint (eg, bitten on hand and swelling above elbow); any bite around head or neck considered severe; compartment syndrome—rare because most snakes envenomate into subcutaneous area of skin and do not break fascial plane (dramatic swelling, but not compartment syndrome); systemic toxicity—patients do not feel well, eg, nausea and vomiting, metallic taste in mouth |
| Management: place 2 large-bore intravenous (IV) lines; speaker immediately elevates extremity (once in hospital, want to limit tissue injury and deliver venom centrally where antivenin can take effect); type and crossmatch blood; tetanus prophylaxis and prophylactic antibiotics appropriate; screen with international normalized ratio (INR), platelet count, standard sequential multiple analysis (SMA), and urine dipstick |
| Determining severity: combine local and systemic toxicity to determine severity of envenomation; no systemic toxicity if no signs of local envenomation; in mild poisoning, little local pain and swelling, no systemic toxicity; poisoning moderate if any systemic toxicity or progressive swelling; envenomation severe if end-organ manifestation and much progressive swelling present |
| Antivenin therapy: CroFab new sheep-derived antivenin; has dramatically increased safety of antivenin therapy (no anaphylaxis, although minor allergic reactions may occur); starting dose 4 to 6 vials, then dose progressively based on patient’s condition, ie, if swelling stops and systemic signs resolve, stop antivenin; if swelling continues, continue antivenin; doses can get very large; expensive (2 vials cost $1600 wholesale); patients often need repeated care |
Educational Objectives
| The goal of this program is to educate the listener about bite injuries. After hearing and assimilating this program, the clinician will be better able to: |
| 1. Review the management of dog bites. |
| 2. Describe potential injuries from cat bites. |
| 3. Explain how to manage clenched-fist injuries. |
| 4. Discuss the epidemiology and vectors of rabies. |
| 5. Describe the signs and symptoms of snake envenomation. |
Discussed on This Program
Amoxicillin and potassium clavulanate (co-amoxiclav) [Augmentin] Azithromycin [Zithromax] Clindamycin (many trade names) Dicloxacillin sodium [Dycill, Dynapen, Pathocil] Erythromycin (many trade names) Penicillin (many trade names and formulations) Rabies immune globulin, human (RIG) [BayRab, Imogam Rabies – HT2 ] Rabies vaccine [Imovax Rabies Vaccine (Human Diploid Cell), Imovax Rabies I.D. Vaccine (Human Diploid Cell), RabAvert, Rabies Vaccine (Adsorbed)] Tetracycline HCl (many trade names)
Programs of Related Interest
Clark RF, Tomaszewski C: Toxicology update. Audio-Digest Emergency Medicine 21:11(Jun 7), 2004; Linder TF et al: Outdoor hazards. Audio-Digest Family Practice 51:28(Jul 28), 2003; Tenenbein M: Toxicology update. Audio-Digest Pediatrics 49:24(Dec 21), 2003.
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Suggested Reading
Applegate JA et al: Childhood risks from the ferret. J Emerg Med 16:425, 1998; Cowles RA et al: Presentation and treatment of venomous snakebites at a northern academic medical center. Am Surg 69:445, 2003; Dire DJ et al: A prospective evaluation of risk factors for infections from dog-bite wounds. Acad Emerg Med 1:258, 1994; Dire DJ: Cat bite wounds: risk factors for infection. Ann Emerg Med 20:973, 1991 (Erratum 21:1008, 1992); Goswami A et al: The real cost of rabies post-exposure treatments. Vaccine 23:2970, 2005; Robbins A et al: Bat incidents at children’s camps, New York State, 1998-2002. Emerg Infect Dis 11:302, 2005; Schier JG et al: Efficacy of Crotalidae polyvalent antivenin for the treatment of hognosed viper (Porthidium nasutum) envenomation. Ann Emerg Med 41:391, 2003; Talan DA et al: Bacteriologic analysis of infected dog and cat bites. Emergency Medicine Animal Bite Infection Study Group. N Engl J Med 340:85, 1999; Van den Enden E: Prophylaxis against rabies. N Engl J Med 352:1608, 2005.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial relationship with the manufacturer or provider of any commercial product or service discussed. For this issue, the faculty reported nothing to disclose.
Dr. Weber was recorded October 25, 2004, in San Francisco, at Topics in Emergency Medicine, sponsored by the University of California, San Francisco, School of Medicine; Dr. Hoffman, July 6, 2004, in Bolton Landing, New York, at the 2004 Scientific Assembly of the New York Chapter of the American College of Emergency Physicians. The Audio-Digest Foundation thanks the speakers and the sponsors for their cooperation in the production of this program.
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