Is this bite cause for hospital admission?

A 27-year-old woman was petting her cat, when the animal suddenly bit her on the arm. She immediately rinsed copiously with isopropyl alcohol and applied an over-the-counter antibiotic ointment. However, 12 hours later a large, red, swollen, and exquisitely tender plaque had developed around the bite site (Figure). There was purulent drainage at the bite site. The patient was being treated for Crohn disease, receiving periodic infliximab infusions and taking 6-mercatopurine. The remainder of the medical history, as well as social and family histories, were unremarkable. The patient calls you for advice. What would be the best thing to do?

A. Call in a prescription for 7 days of oral cephalexin
B. Reassure her that this is a normal response to toxins in cat saliva and suggest frequent warm tap water soaks and oral NSAIDs, as needed, for pain
C. Call in a prescription for oral cephalexin and recommend frequent warm tap water soaks
D. Tell her to take the cat to the local public health department immediately for quarantined observation for rabies
E. Tell her to report to the nearest ED, with anticipation of hospitalization for parenteral antibiotics and surgical consultation

Answer on next page...

Answer: Tell her to report to the nearest ED, with anticipation of hospitalization for parenteral antibiotics and surgical consultation (E)

Discussion
It has been estimated that nearly one half of all American households own pets. The incidence of companion animal bite wounds is approximately 2 million cases each year, accounting for 1% of all emergency room visits annually.¹ The vast majority of bite wounds are inflicted by dogs; these rarely result in hospitalization and carry a low risk of infection. By contrast, the second most common, cat bites, become clinically infected at a rate of 30% to 50%-well over double the rate for dog bites.² The morphology of the animals’ teeth is responsible for this disparity; the sharp, needle-like feline teeth inflict a small, initially innocuous-appearing puncture wound, which often leads to delay in diagnosis and treatment. In fact, these wounds can inoculate deep musculoskeletal structures, resulting in cutaneous cellulitis, deep abscess formation, purulent tenosynovitis and myositis, true septic arthritis, and even osteomyelitis.

Predictive risk factors for severe infection include diabetes, chronic liver, renal, or lung disease, and immunosuppressive conditions or medications. The degree of tissue damage, depth of penetration, and delay in presentation also affect morbidity.³ Significant risk factors for poor outcome in this case are the patient’s iatrogenic immunosuppression, a deeply penetrating bite, and a delay in seeking medical attention. Clinical evaluation, coupled with a plain radiograph, musculoskeletal ultrasonography, and MRI, may all be required to determine whether aspiration and/or surgical debridement is required. For this patient, a do-it-yourself home remedy is not sufficient.

Infected cat bite wounds are polymicrobial in two-thirds of cases; the majority of infections involve both aerobes and anaerobes.⁴ The predominant and most frequent microorganism cultured is Pasteurellamultocida, which is part of the natural oral flora of domestic cats. Pasteurella multocida wound infection is characterized by onset of a local intense cellulitis within 24 hours following the bite. Inadequately treated, infection with this organism may also produce purulent destruction of deeper soft tissue structures.

In addition to Pasteurella, cat bite wounds may also be infected with various species of streptococci, less commonly staphylococci, and commonly with anaerobes, such as assorted species of Fusobacterium, Porphyromonas, and Prevotella.⁵ Aggressive antibiotic therapy should be initiated as soon as possible following a cat bite to treat cellulitis and to prevent other complications. Empirical oral or intravenous antibiotics are directed against the most common organisms isolated. Outpatients are optimally treated with amoxicillin clavulanate.^1,3,6 Alternatives for patients allergic to penicillin include doxycycline, tetracycline, and ciprofloxacin.⁷ First-generation cephalosporins, erythromycin, clindamycin, and aminoglycosides are frequently ineffective and so are not recommended. Thus, cephalexin is not a good choice for this patient.

In a well cared-for house pet with up-to-date vaccinations (as in this case) there is little worry about rabies. In domestic animals, such as cats and dogs, rabies is quite rare in the United States. Most human rabies cases in this country have been associated with rabid bats, while in developing countries, dogs are the most common animals implicated in the transmission of rabies to humans.⁸
 

References:

References1. Kwo S, Agarwal JP, Meletiou S. Current treatment of cat bites to the hand and wrist. J Hand Surg. 2011;36:152-153.
2. Benson LS, Edwards SL, Schiff AP, et al. Dog and cat bites to the hand: treatment and cost assessment. J Hand Surg. 2006;31:468-473.
3. Lewis KT, Stiles M. Management of cat and dog. Am Fam Physician. 1995;52:479-485.
4. Talan DA, Citron DM, Abrahamian FM, et al. Bacteriologic analysis of infected dog and cat bites. N Engl J Med. 1999;340:85-92.
5. Abrahamian FM, Goldstein EJC. Microbiology of animal bite wound infections. Clin Microbiol Rev. 2011;24:231-246.
6. Griego RD, Rosen T, Orengo IF, et al. Dog, cat, and human bites: a review. J Am Acad Dermatol. 1995;33:1019-1029.
7. Freshwater A. Why your housecat's trite little bites could cause you quite a fright: a study of domestic felines on the occurrence and antibiotic susceptibility of Pasteurella multocida. Zoonoses Public Health. 2008;55:507-513.
8. Blanton JD, Robertson K, Palmer D, et al. Rabies surveillance in the United States during 2008. J Am Vet Med Assoc. 2008;235:676-689.