Rationale:

• The most common bacteria isolated from infected cat bites are P. multocida, Streptococcus species (approximately 50% S. mitis), Staphylococcus species (only 4% S. aureus), Moraxella, and various anaerobes, all of which are susceptible to amoxicillin-clavulanate or ampicillin-sulbactam.
• Initial coverage of infected cat bites should be broad because most infections are polymicrobial.
• P. multocida, which is implicated in approximately 75% of cat bite infections, is not susceptible to first generation cephalosporins, antistaphylococcal penicillins, clindamycin, or erythromycin alone.
• Inappropriate initial antibiotics increase the rate of cat bite infectious complications.
• Untreated P. multocida infection can lead to substantial morbidity, including osteomyelitis, septic arthritis, meningitis, bacteremia, endocarditis, and spontaneous bacterial peritonitis.

Evidence:

• The median number of bacteria isolated per cat bite infection was 5, of which 63% were mixed aerobe and anaerobe, in a prospective emergency department series of 57 consecutive infected cat bites (19).
• P. multocida (75%), Streptococcus (46%), Staphylococcus (35%), Moraxella (35%), Corynebacterium (28%), and Neisseria (19%) were the most commonly isolated aerobic bacteria in a prospective case series of 57 consecutive cat bite infections. The most common anaerobes isolated were Fusobacterium (33%), Porphyromonas (30%), Bacteroides (28%), Prevotella (19%), and Propionibacterium (18%) (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).
• A retrospective study of 14 patients admitted for P. multocida animal bite wound infections (9 cat bite infections) revealed that 10 patients were administered inappropriate antibiotics before hospitalization. The most commonly prescribed inappropriate antibiotic was flucloxacillin (8/10), an antistaphylococcal penicillin (26).
• P. multocida can cause spontaneous bacterial peritonitis with a mortality rate near 33% (62).

Comments:

• Recognize that cat bites can also transmit Bartonella henselae, which can cause cat scratch disease, bacillary angiomatosis, and peliosis hepatis. Typical cat scratch disease usually causes localized lymphadenitis with mild systemic symptoms occurring in 25% of patients. Antibiotic therapy has not been shown to alter its clinical course. Uncomplicated cases of cat scratch disease are self-limited and usually resolve within 3 months without specific therapy.
• Complications of cat scratch disease are uncommon and include encephalitis, osteomyelitis, endocarditis, fever of unknown origin, and erythema nodosum. Bacillary angiomatosis and peliosis hepatis are atypical manifestations of cat scratch disease and require intravenous antibiotic therapy, usually with a macrolide or tetracycline antibiotic.
• Although rare, cat bites can also transmit tularemia (Francisella tularensis), plague (Yersinia pestis), and possibly Q fever (Coxiella burnetii).