Small wounds that involve no tendons or joints that present within 8 hours and that can be adequately debride and irrigated, are low-risk injuries for infection. Higher-risk wounds, then, are seen with:
- delayed presentation (8 hours or more)
- puncture injuries — that cannot be debrided adequately
- clenched-fist injuries
- hands, feet, or facial injuries
- human bites – more likely to have gram-negative bacteria and anaerobes, some of which are likely β-lactamase producers
- deeper tissue involvement — bones, joints, tendons
- immunocompromised patients
In otherwise healthy people with a low risk of infection, most bite and clenched fist injuries can be managed with good wound care alone. Boils can generally be tested with incision and drainage without the need for antibiotics. The strongest evidence for prophylactic antibiotics is for bite wounds on the hands, especially where wounds penetrate tendon sheaths or the mid-palmar space.
Of community-acquired Staph infections, often skin/soft tissue infections:
- 18% were methicillin resistant (MRSA):
- 40% resistant to erythromycin and ciprofloxacin
- 15% resistant to tetracycline
- 10% resistant to gentamycin or trimethoprim-sulphamethoxazole
First-line management for all bite and clenched fist injuries includes thorough cleaning, debridement, irrigation, elevation and immobilisation. Always check whether tetanus immunisation is up to date.
With established infections, use a combination of clinical history, visual inspection, infected tissue gram stain/culture and susceptibility testing to inform choice and duration of antibiotics when they are indicated.
Cleaning, debridement, irrigation, elevation and immobilisation are the recommended first-line management for bite and clenched fist injuries.
Animal bites and the risk of infection (most frequent to least frequent):
- Human — 10-15% become infected (“bacterial inoculum of human bite wounds contain as many as 100 million organisms per milliliter of as many as 190 different specie”).
- Cat — 15% (28-80%) become infected (sharper teeth cause puncture wounds; Pasteurella multocida).
- Dog — 5% (3-18%) become infected (Pasteurella canis, manifests as rapidly spreading cellulitis) but they are by far the most common (80-90%) of all animal bites.
References:
- Take a bite out of resistance. NPS MedicineWise News, Dec 2015.
- Jeffrey Barrett J, Brusch JL, Revis DR Jr. Human Bites. Medscape.
- Dire DJ. Cat bite wounds: risk factors for infection. Ann Emerg Med. 1991 Sep;20(9):973-9.
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