Cat Bites

A 50 year-old man presented to the ED after having sustained several cat bites and scratches to his left hand three hours prior to arrival while separating his fighting pets.  The patient was a known Type II diabetic and also allergic to penicillin (manifested by immediate hives).  The patient was afebrile and exhibited several cat bite punctures on the dorsum of his hand, in addition to several other scratches.  His exam is depicted in the video below, during which he is asked to make a fist.

Review the video and carefully review the x-rays and consider how you would treat this patient.  Of note, the erythema was circled with a pen upon arrival to the ED, and the video was taken less than one hour later.

The presentation of this infected cat bite is notable for:  a) The aggressive nature of the infection.  As noted, the findings on exam have all appeared in the three short hours following the bite.  Already the patient exhibits marked erythema, edema, and limitation of flexion of his fingers.  Note that in the hour since the visible erythema was circled, it is already seen to extend beyond the ink mark on the video. b)  The finding of air in the soft tissues along the dorsum of the hand on the lateral X-ray of the hand.

Infected cat bites tend have a complex microbiologic mix (2).  However, in this particular case, two specific pathogens must be targeted when considering treatment:

1)  Pasteurella multocida.  More than 50% of cat bite wounds become infected and P. multocida is found as a pathogen over 75% of the time (3).  Infection with P. multocida is characterized by extremely rapid onset. Local pain and inflammation often occur within 4 to 6 hours of the injury and almost always within 24 hours. This patient did not exhibit purulent discharge, which is seen with P. multocida in 40% of cases (3).

2)  Beta hemolytic streptococcus.   This pathogen is also a common cause of cat bite infections and also is known to be associated with a rapid onset of infection.  The air in the soft tissues suggests streptococcal infection, but it is by no means pathognomonic.  

Ampicillin/sulbactam would have been chosen to treat this patient if not for his penicillin allergy.  The choice of antibiotics in penicillin-allergic patients is more difficult and is based primarily on in vitro sensitivity since data on clinical efficacy are less than adequate (5). This patient was started on intravenous doxycycline (coverage against P. Multocida) and clindamycin (excellent streptococcal coverage).  The plan was to closely follow the patient clinically and if there was no improvement, to have him undergo surgical incision and drainage.  In fact, the patient exhibited dramatic improvement by the next morning such that he went home after 48 hours in the hospital, on oral antibiotics.



References:

(1) Goldstein EJC: Bite wounds and infection. Clin Infect Dis 1992;14:633-8.

(2)  Talan DA, et al.  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.

(3)  Mandell: Principles and Practice of Infectious Diseases, 5th ed., Copyright 2000 Churchill Livingstone, Inc.

(4)  Schlossberg: Current Therapy of Infectious Disease, 2nd ed., Copyright 2001 Mosby 

(5)  Fauci: Harrison 's Principles of Internal Medicine, 14th ed.  Copyright 1998 McGraw Hill

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