Infectious Disease Compendium

Cat Bite


"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.


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).

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.


Cats teeth are like needles and inject bacteria deep into tissue. 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 patients will seroconvert and maybe a quarter will have evidence of a blood stream infection (PubMed).


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 over rated as a source of toxoplasmosis. It's mostly from undercooked meat.

Curious Cases

Relevant links to my Medscape blog

Itchy Red Bumps

Do I believe it?

Last Update: 05/29/18.