Rationales

The recommendations in this guideline are based on the evidence identified and the experience of the committee.

Assessment

Why the committee made the recommendations

Recommendations 1.1.1 to 1.1.3

The committee agreed that it was good practice to assess and manage the wound in line with NICE's clinical knowledge summary on human and animal bites. They also agreed that, for human and animal bites, healthcare professionals should also consider potential safeguarding issues for vulnerable adults and children in line with NICE guidelines.

There was only evidence on managing bites from humans, dogs and cats; no evidence was identified for bites from other animal species. The committee agreed that it was reasonable to extrapolate this evidence to bites from other animals traditionally kept as pets, such as rabbits and hamsters. The committee agreed that specialist advice should be sought for bites from wild and exotic animals (including birds and non-traditional pets), such as snakes, lizards, monkeys or bats. This was because there may be a different spectrum of bacteria involved and a risk of other serious non-bacterial infections. For example, monkey bites are associated with herpes B virus, which may have serious consequences if not treated early, including fatal encephalomyelitis or severe neurological impairment. Healthcare professionals may also wish to seek specialist advice for domestic animal bites (including farm animal bites) they are not familiar with.

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Antibiotic prophylaxis for uninfected human and animal bites

Why the committee made the recommendations

Recommendations 1.1.4 to 1.1.12

Evidence was only identified for antibiotic prophylaxis after a dog, cat or human bite, and it was limited and of low quality. The committee agreed that, if a bite has not broken the skin, antibiotic prophylaxis is not needed. Many bites are superficial abrasions, meaning that they break the skin but do not draw blood. These bites are at low risk of infection because the dermis will not have been penetrated, so do not always need antibiotic prophylaxis.

The committee went on to discuss and agree when antibiotic prophylaxis should either be offered, considered, or not offered for a human, cat or dog (or other traditional pet) bite, based on the evidence and their knowledge of the risk of infection.

The committee discussed the pooled evidence on human bites, which suggested that antibiotic prophylaxis was more effective than placebo at reducing the incidence of infection. They discussed that a human bite that has broken the skin is at high risk of infection and other serious consequences because of the associated oral bacteria. However, they also discussed that the site and depth of a bite affects the risk of infection. In a study of human bites to the hand, antibiotic prophylaxis was particularly effective. The committee discussed that wounds to the hand have a higher risk of infection because of the multiple small compartments and number of joints. The same high level of infection risk applies to the feet and skin overlying cartilaginous structures.

The committee went on to discuss the evidence for human bites that are at lower risk of infection, as outlined in Broder et al. (2004). These bites penetrated only the epidermis (that is, they broke the skin but did not draw blood) and did not involve the high-risk areas of the hands, feet, or skin overlying joints or cartilaginous structures. For this study, there was a very low rate of infection; signs of infection were seen in 1 of 62 people in the placebo group and none of the 63 people taking antibiotics.

The committee agreed that, if a human bite has not broken the skin, antibiotic prophylaxis should not be offered. If it has broken the skin and drawn blood, antibiotic prophylaxis should be offered. The committee agreed that, for people with a human bite that has broken the skin but not drawn blood, antibiotic prophylaxis is not routinely needed. However, they agreed that it can be considered for bites in high-risk areas or in people at risk of a serious wound infection because of a comorbidity.

The committee went on to discuss when antibiotic prophylaxis should be offered for a cat bite. The evidence on cat bites, which was based on a very small sample size of 11 did not show a statistically significant difference between antibiotic prophylaxis and placebo in reducing the incidence of infection in cat bites. Based on such limited data, the committee could not judge the certainty of the evidence. However, based on their expertise and experience, they agreed that antibiotic prophylaxis should be offered if a cat bite has broken the skin and drawn blood. Cat bites are at high risk of infection because of cat oral bacteria and because the needle-like nature of the wounds (small, deep punctures) is hard to irrigate. The committee went on to discuss that this type of wound is often deeper than it appears, which can cause assessment difficulties. They also noted that infection in deep skin structures is possible, which has serious consequences such as bone infections. The committee agreed that antibiotic prophylaxis is not needed if a cat bite has not broken the skin. However, it can be considered if the cat bite has broken the skin but not drawn blood if, despite appearances and the lack of blood, the wound could still be deep.

The committee went on to discuss and agree situations when antibiotic prophylaxis should be offered for a dog bite (or a bite from another traditional pet other than a cat). Evidence suggested no difference between antibiotic prophylaxis and placebo in reducing the incidence of infection based on the type and location of the dog bite wound. However, based on their experience, the committee agreed that antibiotic prophylaxis should be offered for a dog bite (or a bite from another traditional pet) if it:

  • has broken the skin and penetrated bone, joint, tendon or vascular structures or

  • is deep, a puncture or crush wound, or has caused significant tissue damage or

  • is visibly contaminated (for example, if there is dirt or a tooth in the wound).

They also agreed that antibiotic prophylaxis could be considered for a dog bite (or a bite from another traditional pet other than a cat) that has broken the skin and drawn blood if it involves a high-risk area or is in a person at risk of a serious wound infection because of a comorbidity. The committee agreed that the principles of the evidence from Broder et al. (2004) on human bites could be extrapolated to bites from dogs or other traditional pets). The committee discussed that antibiotic prophylaxis would only be considered for a dog bite (or a bite from another traditional pet) fulfilling these criteria because, in their experience, these bites have a lower risk of infection than human bites. This is supported by the evidence that showed no difference between antibiotic prophylaxis and placebo in reducing the incidence of infection after a dog bite. Antibiotic prophylaxis is not needed for a dog bite (or a bite from another traditional pet) that has not broken the skin, or has only caused a superficial wound that has broken the skin but not drawn blood.

For more details, see the summary of the evidence on antibiotics.

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Treating infected human and animal bites

Why the committee made the recommendations

Recommendations 1.1.13 to 1.1.14

There was no evidence on the treatment of human or animal bites. However, the committee agreed that antibiotics should be offered for human or animal bites with symptoms or signs of infection because of the potential consequences of not treating an infected bite.

The committee also agreed that, if there is discharge from the bite wound this should be swabbed and sent for microbiological testing before antibiotics are taken. This includes purulent and non-purulent discharge because certain bacteria associated with a human or animal bite, such as Eikenella, may not form pus.

For more details, see the summary of the evidence on antibiotics.

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Reassessment

Why the committee made the recommendations

Recommendations 1.1.16 to 1.1.18

The committee agreed that a human or animal bite should be reassessed if an infection develops or worsens rapidly or significantly at any time or does not start to improve within 24 to 48 hours of starting treatment because of the consequences of complications from an infection. Reassessment is also recommended if the person becomes systemically unwell or has severe pain that is out of proportion to the infection (which can be a symptom of necrotising fasciitis).

The committee agreed that it is good antimicrobial stewardship to review and potentially change the antibiotic used when microbiological testing results are available. A narrow-spectrum antibiotic should be used if appropriate.

They also discussed that reassessment is another opportunity to reconsider potential safeguarding issues for vulnerable adults or children, and to consider non-verbal signs of pain, such as a change in behaviour, in people who have difficulty communicating.

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Referral and seeking specialist advice

Why the committee made the recommendations

Recommendations 1.1.19 to 1.1.20

The committee agreed that people with a human or animal bite should be referred to hospital if they have symptoms or signs of a more serious illness or condition, or if they have penetrating wounds with certain features because of the serious consequences of these.

The committee agreed other circumstances when the prescriber may want to refer the person or seek specialist advice.

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Choice of antibiotic

Recommendations 1.2.1 to 1.2.3

Why the committee made the recommendations

No evidence was found comparing different antibiotics to inform the choice of antibiotic for human and animal bites. Therefore, the committee based these recommendations on their experience, current practice, antimicrobial resistance, and the need to provide choices that cover the relevant range of likely aerobic and anaerobic pathogens in human and animal bites.

The committee agreed that the same antibiotic choices should be available for both prophylaxis and treatment because the pathogens will be the same.

Oral antibiotics

The committee agreed that the first-choice oral antibiotic for all people with a human or animal bite is co‑amoxiclav, which has good activity against the relevant range of likely pathogens.

The committee were aware of the BNF entry for co‑amoxiclav. Advice was also sought from the UK Teratology Information Service (UKTIS), which confirmed that the association between co‑amoxiclav and necrotising enterocolitis has only been identified in the context of prelabour premature rupture of the membranes (PPROM). Outside of this, there is no evidence to show that general co‑amoxiclav use in pregnancy is associated with an increased risk of necrotising enterocolitis. UKTIS advised that there should be no restriction around the use of co‑amoxiclav in pregnancy, provided it is not being given for PPROM. It was agreed that human or animal bites are a suitable clinical indication for co‑amoxiclav use in pregnancy.

If co‑amoxiclav is unsuitable, the alternative first-choice oral antibiotics for adults and young people over 12 years are doxycycline with metronidazole (an antibiotic with high activity against anaerobic bacteria). If co‑amoxiclav is unsuitable and a woman is pregnant, specialist advice should be sought for an alternative antibiotic with good activity against Pasteurella.

The committee agreed that if co‑amoxiclav is unsuitable, the alternative first-choice oral antibiotic for children under 12 years is co‑trimoxazole because this also has good activity against the range of likely pathogens.

Intravenous antibiotics

The committee agreed that intravenous antibiotics should only be used if a person cannot take oral antibiotics or the severity of their condition warrants intravenous antibiotics. The first-choice intravenous antibiotic for all people with a human or animal bite is co‑amoxiclav because it has good activity against the relevant range of likely pathogens.

If co‑amoxiclav is unsuitable, the alternative first-choice intravenous antibiotics for all people with a human or animal bite are:

  • cefuroxime with metronidazole

  • ceftriaxone with metronidazole.

The committee agreed that both options have good activity against the relevant likely pathogens. The cephalosporins, cefuroxime and ceftriaxone have a similar spectrum of activity but providing more than 1 option allows for choice to be made locally. If a cephalosporin is not appropriate, for example, in people with a history of immediate hypersensitivity to penicillins, the committee agreed that a local microbiologist should be consulted to suggest a suitable alternative.

Dosage, course length and route of administration

There was no evidence comparing antibiotic dosage, course length and route of administration. Therefore, the recommendations were based on the committee's experience and current practice. The committee agreed that the shortest course that is likely to be effective should be prescribed to reduce the risk of antimicrobial resistance and adverse effects. However, because the type and severity of bites can vary, a longer course may be needed based on clinical assessment of the wound.

The committee agreed that, for both oral and intravenous routes of administration (which would be switched to oral antibiotics when possible), a course length of 3 days should be effective for prophylaxis, and a course length of 5 days should be effective for treatment. However, the committee discussed that because the type and severity of bites can vary, a longer course of up to 7 days (with review) may be needed. This would be based on a clinical assessment of the wound, and whether it has, for example, caused significant tissue destruction or penetrated bone, joint, tendon or vascular structures.

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  • National Institute for Health and Care Excellence (NICE)