Diagnosis
"I was bit by a cat".Epidemiologic Risks
"Kitty kitty kitty here nice kitty kitty, damn it, it bit me in the hand." Often in the space between the thumb and first finger.
Microbiology
S. aureus, Streptococci, anaerobes and Pasteurella.
When tested by 16S ribosome methodology the wounds are filled with difficult to grow anaerobes, that, when grown, are ampicillin susceptible (Pubmed).
Cats to human Mycobacterium bovis (Pubmed).
Empiric Therapy
Amoxicillin-clavulanic acid for prophylaxis OR doxycycline alone of allergic.
For real infections use real antibiotics directed against the flora of the cat mouth.
Ampicillin or third-generation cephalosporins PLUS metronidazole would be good choices.
If PCN allergic use a quinolone PLUS (clindamycin OR metronidazole) OR doxycycline alone.
Pasteurella are usually resistant to first-generation cephalosporins.
Specific Therapy
Debride, then prophylaxis for 10 days. And don't forget the tetanus booster. You did, didn't you? Treat soft tissue infections (cellulitis or abscess) with iv until afebrile, then po for a total of 10-14 days.
Septic arthritis or tenosynovitis is 2 -3 weeks of iv.
Osteomyelitis is usually 6 weeks of iv.
Pearls
Cat's teeth are like needles and inject bacteria deep into tissues. This makes debridement difficult if not impossible and makes joint infections likely. They say that Pasteurella infections start in the first 48 hours after the bite and that staphylococcal and mixed infections take longer to manifest.
Almost always call a hand surgeon. Just in case. Unless, of course, the bite was not on the hand.
The majority of patients after a scratch will have symptoms of Bartonella (fatigue, arthralgias, and myalgias), half of the patients will seroconvert and maybe a quarter will have evidence of a bloodstream infection (PubMed).
Rants
Cats really are vermin that serve no useful purpose but to spread disease. And. Some epidemiologic data suggest cat scratches and bites increase the risk of depression (PubMed). I'd be depressed if I had to own a cat.
Raw cat food is the source of ESBL producing Enterobacteriaceae in cat shit. And cats do lick their butts before they bite you. So there is more than Toxoplasma in that litter box (PubMed). As an aside, cat shit is way overrated as a source of toxoplasmosis. It's mostly from undercooked meat.
Curious Cases
Relevant links to my Medscape blog
Last Update: 05/29/18.