Editors

IiroJääskeläinen

Bite Wounds

Remember tetanus prophylaxis.
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.
Cleaning of the wounded area as early and carefully as possible 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.

Most bite injuries are caused by dogs, cats or humans, in this order.
About 15-25% of human bites, 5-25% 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 theoretically be transmitted through a human bite.
Infective microbes usually belong to the normal flora of the biter's mouth. Sometimes the microbes derive from the victim's skin or the environment.
Scratch wounds are assessed on a case-by-case basis. Skin-piercing injuries and clinically infected superficial animal nail scratches are treated similarly to bite wounds if needed.
Signs of infection may include e.g. tenderness, redness, swelling, clear or purulent secretion, local swelling of the lymph nodes or restriction of range of motion.

Cleaning and local treatment performed as early 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 0.9 % NaCl; 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).

Primary wound closure is possible in mild uninfected cases, especially in the facial area.
- Facial wounds are usually sutured for cosmetic reasons.
- Wounds in the hands and lower extremities are usually left open to avoid infection.
Primary closure should not be performed for bite wounds older than 12 hours.
Infected bite injuries are not closed initially.
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.

Prophylaxis has not been shown with certainty to be effective in the prevention of infection. The use of antimicrobials does not replace prevention, early cleaning, local treatment, elevated position and follow-up in the treatment of bite wounds.
The earlier the bite is cleaned and, if necessary, débrided, the lower the risk of infection.
A 3-5 day prophylaxis is recommended for high-risk bites.
- Moderately severe bites
- Bites caused by a cat or human
- Bites on the hands and genitals
- When the injury may extend to a bone or joint or is close to an artificial joint
- In immunodeficient persons (high alcohol consumption, asplenia, underlying disease, systemic medication)
- Disorders of blood or lymphatic circulation in the extremities (diabetes, arteriosclerosis obliterans)
Dog bites become infected much less often than bites caused by cats and humans. Routine prophylaxis is not recommended when treatment is sought quickly and the bite is not a high-risk bite.
- Prophylaxis should be considered forwounds that have not been cleaned for more than 8 hours and where symptoms prompt the patient to seek treatment.
Prophylaxis is not required if the bite is more than 3 days old and no signs of infection are detected.

The prophylaxis used is
- primarily amoxicillin-clavulanic acid (for an adult 500/125 mg three times daily)
- alternatively, a combination of tetracycline (doxycycline 100 mg twice daily) and metronidazole (400 mg 3 times daily).
In penicillin-allergic patients, children and pregnant women,azithromycin orclarithromycin may need to be used in outpatient care, and in patients allergic to several antimicrobials,moxifloxacin or a combinationof levofloxacin and metronidazole.

When using the same antimicrobials as in prophylaxis, 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 therapy are indicated when the victim has general symptoms, is immunocompromized or has low compliance to treatment.
- Empirical intravenous treatment is primarily started with the combination of cefuroxime and metronidazole; except, in human bites, moxifloxacin or a carbapenem is used.
Control an infected wound after 24-48 hours.

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]