Rationale:

• The most common isolates from infected dog bites are Pasteurella species (P. canis or P. multocida), Streptococcus species (approximately 50% S. mitis), Staphylococcus species (approximately 50% S. aureus), Neisseria species, and various anaerobic bacteria, all of which are usually susceptible to amoxicillin-clavulanate or ampicillin-sulbactam.
• Broad coverage is essential in treating bite wound infections because most infections are polymicrobial.
• Capnocytophaga canimorsus, which can cause severe infections with a case-fatality rate of 25%, is also susceptible to penicillins, including amoxicillin or ampicillin.
• Pasteurella species are poorly susceptible to first generation cephalosporins, antistaphylococcal penicillins, clindamycin, and erythromycin, and these should never be used as monotherapy in infected dog bite wounds.
• Staphylococcus aureus is resistant to penicillin, and therefore penicillin should not be used as monotherapy.
• Newer fluoroquinolones have expanded activity against anaerobic bacteria, in addition to covering most bite wound aerobic bacteria, and can be used as monotherapy.
• Capnocytophaga canimorsus is resistant to co-trimoxazole and antipseudomonal aminoglycosides.

Evidence:

• A prospective study of infected animal bites (50 dog bites) seen in 18 emergency departments showed that the median number of bacteria isolated per dog bite infection was 5, of which 48% were mixed aerobic and anaerobic infections (19).
• The following bacteria were the most frequent aerobic and anaerobic bacteria isolated in 50 consecutive infected dog bite wounds seen in a prospective emergency department series. The most common aerobic bacteria isolated were Pasteurella species (50%), Streptococcus species (46%), Staphylococcus species (46%), Neisseria species (16%), and Corynebacterium species (12%). Capnocytophaga canimorsus was isolated in 2% of this series of bite wound infections. The most common anaerobic bacteria isolated were Fusobacterium (32%), Bacteroides (30%), Porphyromonas (28%), Prevotella (28%), and Propionibacterium (20%) (19).
• Treatment recommendations are based on in vitro susceptibility patterns and minimum inhibitory concentrations of antibiotics obtained from multiple review articles because in vivo studies are not available (3; 12; 57).
• Capnocytophaga canimorsus can lead to sepsis with a high mortality rate, as well as other infectious complications, including endocarditis, mycotic aortic aneurysms, and brain abscesses (58; 59; 60; 61).

Comments:

• None.