Swelling and pain 2 weeks after a dog bite
A 48-year-old man with gout, multiple sclerosis, and previously treated methicillin-resistant Staphylococcus aureus (MRSA) infection presented to the emergency room with pain and significant swelling at the site of a dog bite on his left forearm. He had been bitten 2 weeks earlier by a friend’s dog, and the bite had punctured the skin. He also had red streaking on the skin of the left arm from the wrist to the elbow, and he reported feeling “feverish” and having night sweats.
At first, the bite had seemed to improve, then swelling and pain had developed and increased. He reported this to his primary care physician, along with the information that he had previously had an anaphylactic reaction to penicillin and a cephalosporin. His physician, considering a penicillin allergy, started him on ciprofloxacin (Cipro) plus clindamycin (Cleocin). The patient took this for 5 days, but without improvement. The appearance of the red streaking on his left forearm prompted his presentation to our emergency room.
ORGANISMS IN DOG BITES
1. Which is the most common cause of infected dog bite?
- Pasteurella canis
- Streptococci and S aureus
- Erysipelothrix rhusiopathiae
- Capnocytophaga canimorsus
- Eikenella corrodens
Streptococci (50%) and S aureus (20% to 40%) are the organisms most commonly responsible for infected dog bites, as they are for other skin and soft-tissue infections.1P canis is unique to dog bite infections but accounts for only 18%.2E rhusiopathiae is an unusual isolate from cat and dog bites and is more commonly isolated from the mouths of fish and aquatic mammals. C canimorsus is a normal inhabitant of the oral cavity of dogs and cats but an unusual cause of wound infection from a dog bite. It is notable for sepsis and central nervous system infections uniquely associated with veterinarians, dog owners, kennel workers, and mail carriers.3E corrodens infection is more common with human bites.4
THE EVALUATION BEGINS
On examination, the patient had marked edema of the left forearm and pain in the joints of the left hand. His temperature was 100.2°F (37.9°C). Because of the duration and severity of symptoms, the examining physician was concerned about septic arthritis of the wrist, and the patient was admitted to the hospital.
In the hospital, our patient was thermodynamically stable without documented fever or chills. There was no open wound to culture, and blood cultures were negative. Marked edema and joint involvement raised suspicion of erysipeloid. This “cousin” of erysipelas often involves the underlying joint, is associated with edema, and produces systemic manifestations of fever and arthralgia.
Radiography of the left forearm and hand demonstrated multiple foci of demineralization within the carpal bones and proximal radius, attributed to disuse. Magnetic resonance imaging (MRI) the next day showed multiple bone infarcts in the carpal bones and the distal radius, with synovitis and fluid in the carpal joints and without adjacent osteomyelitis. Fluid was also seen in the soft tissues in the ulnar aspect of the left wrist, and tenosynovitis involving the flexor carpi radialis tendon was noted.
Arthrocentesis of his left radiocarpal joint produced synovial fluid negative for crystals and negative on Gram stain; the fluid was also sent for culture. The patient’s tetanus immunization was current, and the dog was known to have been immunized against rabies.
ANTIBIOTICS FOR INFECTED DOG BITES
2. Which antibiotic regimen would you choose for this patient?
- Oral amoxicillin and clavulanate
- Meropenem
- Vancomycin, clindamycin, aztreonam
- Clindamycin and levofloxacin
- Clindamycin and trimethoprim-sulfamethoxazole
Oral amoxicillin and clavulanate (Augmentin) is a judicious choice for prophylactic treatment of deep bites in the early stages of infection. However, our patient’s wound was no longer in the early stages of infection, and he had a history of an adverse reaction to penicillin.
Meropenem (Merrem IV) cross-reacts minimally with penicillin allergy and is reported to be safe in patients with a history of anaphylactic reactions to penicillin,5 but overuse of carbapenems has led to the development of carbapenem-resistant strains of Klebsiella, Stenotrophomonas, and Acinetobacter organisms.
Given the rise of MRSA infections and the common involvement of staphylococci, streptococci, and anaerobic bacteria in complicated dog bites, the combination of vancomycin and clindamycin is a good choice, and aztreonam (Azactam) would add empiric coverage of gram-negative enteric organisms.
Levofloxacin (Levaquin) also covers gramnegative enteric organisms, but Fusobacterium canifelinum, a common anaerobe in the oral flora of dogs and cats, is intrinsically resistant to fluoroquinolones.
Clindamycin and levofloxacin would be a good step-down oral regimen. Pasteurella multocida has variable sensitivity to the commonly used agents dicloxacillin (Dynapen), cephalexin (Keflex), macrolides, and clindamycin, but it is a less likely pathogen at this late stage and could be covered with levofloxacin alone.
C canimorsus is resistant to trimethoprim-sulfamethoxazole (Bactrim) and cephalexin, but is well covered by clindamycin.6
