A wound fresher than 12-18 hours is often already heavily swollen but virtually never infected.
Bacterial culture should always be obtained from a suppurative wound that is older than 24 hours. On the request form, the laboratory is informed that the sample is from a bite wound and the species of the biter is mentioned.
Prompt cleaning of the wounded area provides the best protection against infections and cannot be replaced by antimicrobial treatment.
Antimicrobial prophylaxis is recommended in selected cases only.
The risk of rabies Suspicion of Rabies Exposure should be kept in mind especially in travellers. Bites in the extremities and face may also be accompanied with fractures.
General
Most bite injuries are caused by dogs, cats and humans, in this order.
About 10% of human bites, 5-20% of dog bites and 30-60% of cat bites become infected.
Cat bites, large human bites and deep bites by the canine teeth are most sensitive to infection. Cat bites and human bites cause deep tissue complications of infection more often than other bites. Viral hepatitis B and C as well as HIV infection can be transmitted through a human bite.
Infective microbes usually belong to the normal flora of the biter's mouth (staphylococci, streptococci, anaerobes). Sometimes the microbes derive from the victim's skin or the environment.
Clinically infected superficial animal nail scratches are treated similarly to bite wounds if needed.
Treatment of bite injuries
Cleaning and local treatment
Cleaning and local treatment performed as soon as possible provide the most effective protection against infections. Ample amounts of tap water can be used in the initial cleaning; soap is also used if rabies is suspected (neutralizes the virus!).
If the wound is open or has jagged or dangling edges, it is rinsed with pressure by using a 20 ml syringe, 18-20 gauge needle and ample amounts of saline; all wound surfaces are systematically cleaned. This technique cannot be used in deep puncture wounds.
Devitalized tissue is debrided before possible primary closure. Wounds with a high risk of infection require secondary closure which is postponed until antimicrobial treatment is administered. In the treatment of wounds entailing cosmetic (face, genitals) or functional (e.g. wounds distally in the extremities) risks, an assessment by a surgeon is often needed.
In bite wounds of the extremities, elevated position of the extremity to alleviate oedema is almost always needed (sick leave).
Injuries with a probably low infection risk (superficial cat and dog bites) can be sutured or at least the edges of the wound can be secured together with tape.
Bite injuries to the face are usually sutured for cosmetic reasons; bite injuries in the hands are left open to avoid infection.
Antimicrobial prophylaxis in non-infected bite injuries
Prophylaxis has not been shown with certainty to be effective in the prevention of infection Antibiotic Prophylaxis for Bites. The use of antimicrobials does NOT replace prevention, early cleaning, local treatment, elevated position and follow-up in the treatment of bite wounds. Even the best antimicrobial prophylaxis is less effective than early local treatment!
the patient is immunocompromized (heavy alcohol consumption, asplenia, primary disease and systemic medications)
the patient has disturbances of blood or lymph flow in the extremities (diabetes, ASO)
the bite injury is near a joint endoprosthesis
the bite injury is near the genitals
the bite injury is caused by a cat or a human.
The primary prophylaxis is amoxicillin/clavulanic acid (500/125 mg 3 times daily in adults) or the combination of tetracycline (doxycycline 150 mg once daily or 100 mg twice daily) and metronidazole (400-500 mg 3 times daily).
In outpatient care, it may be necessary to use azithromycin or clarithromycin in patients with penicillin allergy, in children and in pregnant women, and moxifloxacin or the combination of levofloxacin and metronidazole in patients with allergy to several antimicrobials.
When using the antimicrobials listed above, the treatment duration in infected, uncomplicated wounds in basically healthy patients is in most cases 5-10 days.
Immobilization of the injured area and intravenous antimicrobials are indicated when the victim has general symptoms, is immunocompromized or is a heavy drinker with low compliance to treatment. Empirical intravenous treatment is primarily started with the combination of cefuroxime and metronidazole; however, if the biter is a human, moxifloxacin or a carbapenem is used.
Control an infected wound after 24-48 hours.
References
Bhaumik S, Kirubakaran R, Chaudhuri S. Primary closure versus delayed or no closure for traumatic wounds due to mammalian bite. Cochrane Database Syst Rev 2019;(12):CD011822. [PubMed]