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BMJ Clin Evid. 2006; 2006: 0914.
Published online 2006 May 1.
PMCID: PMC2907632

Bites (mammalian)

Abstract

Introduction

Mammalian bites are usually caused by dogs, cats, or humans, and are more prevalent in children (especially boys) than in adults. Animal bites are usually caused by the person's pet and, in children, frequently involve the face. Human bites tend to occur in children as a result of playing or fighting, while in adults they are usually the result of physical or sexual abuse. Mixed aerobe and anaerobe infection is the most common type of infection, and can occur in up to half of human bites.

Methods and outcomes

We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of interventions to prevent complications of mammalian bites; and to treat infected mammalian bites? We searched: Medline, Embase, The Cochrane Library and other important databases up to February 2007 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

Results

We found five systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.

Conclusions

In this systematic review we present information relating to the effectiveness and safety of the following interventions: antibiotic prophylaxis (human bites, non-human bites), antibiotics, debridement, decontamination, irrigation, primary wound closure, and tetanus vaccination (after mammalian bites).

Key Points

Mammalian bites are usually caused by dogs, cats, or humans, and are more prevalent in children (especially boys) than in adults.

  • Animal bites are usually caused by the person's pet and, in children, frequently involve the face.
  • Human bites tend to occur in children as a result of playing or fighting, while in adults they are usually the result of physical or sexual abuse.
  • Mixed aerobe and anaerobe infection is the most common type of infection, and can occur in up to half of human bites.

There is consensus that tetanus immunisation should be given routinely as part of wound care of mammalian bites, but no studies have assessed the benefit of this strategy.

  • Immunisation does not need to be performed if there is a record of a tetanus shot having been given in the previous 5 years.

Antibiotics may prevent infection in high risk bites to the hand, but we don't know if it is worth giving prophylactic antibiotics after other types of mammalian bites.

  • High risk bites are those with deep puncture or crushing, with much devitalised tissue, or those which are dirty.
  • Bites that occurred more than 24 hours previously, or those with only simple epidermal stripping, scratches and abrasions, are unlikely to benefit from antibiotic treatment.

There is consensus that wound debridement, irrigation, decontamination and primary wound closure are beneficial in reducing infection, but we don't know this for sure.

There is consensus that antibiotics help to cure infected bite wounds although few studies have been done.

  • Selection of appropriate antibiotics depends on the likely mouth flora of the biting animal and the skin flora of the recipient.

About this condition

Definition

Bite wounds are mainly caused by humans, dogs, or cats. They include superficial abrasions (30-43%), lacerations (31-45%), and puncture wounds (13-34%).

Incidence/ Prevalence

Bite wounds account for about 1-2% of all emergency department visits annually in the USA, costing over US $100 million annually. In the USA, an estimated 3.5-4.7 million dog bites occur each year. About one in five people bitten by a dog seek medical attention, and 1% of those require admission to hospital. Between a third and half of all mammalian bites occur in children. Human bites are the most prevalent mammalian bites after those of dogs and cats, accounting for up to 2-3% of mammalian bites.

Aetiology/ Risk factors

In over 70% of cases, people are bitten by their own pets or by an animal known to them. Males are more likely to be bitten than females, and are more likely to be bitten by dogs, whereas females are more likely to be bitten by cats. One study found that children under 5 years old were significantly more likely than older children to provoke animals before being bitten. One study of infected dog and cat bites found that the most commonly isolated bacteria was Pasteurella, followed by Streptococci, Staphylococci, Moraxella, Corynebacterium, and Neisseria. Mixed aerobic and anaerobic infection was more common than anaerobic infection alone. Human bites commonly occur in children as a result of fighting or playing. In adults, bites commonly occur during physical or sexual abuse. Tooth abrasions to the knuckles (or "clenched fist injuries") can occur during fist fighting.

Prognosis

In the USA, dog bites cause about 20 deaths a year. In children, dog bites frequently involve the face, potentially resulting in severe lacerations and scarring. Rabies, a life threatening viral encephalitis, may be contracted as a consequence of being bitten or scratched by a rabid animal. More than 99% of human rabies occurs in developing countries where canine rabies is endemic. Transmission of rabies from domestic animals such as dogs and cats to humans is extremely rare in the USA, Europe, and Canada. The incidence of rabies transmission in dog bites sustained in Africa, Southeast Asia, and India is significantly higher. Human bites, particularly those to the hand, are often complicated by infection. One study reported infection in 48% of untreated bites to the hand.

Aims of intervention

To prevent or achieve rapid resolution of complications after mammalian bites, with minimal adverse effects.

Outcomes

Prevention of complications: Rate of infection after mammalian bites, incidence of tetanus. Treatment of infected bites: Cure rate of infection owing to mammalian bites.

Methods

Clinical Evidence search and appraisal August 2005. In addition, the authors searched the Web of Science (Science Citation Index to October 2001). The following databases were used to identify studies for this systematic review: Medline 1966 to February 2007, Embase 1980 to February 2007, and The Cochrane Database of Systematic Reviews and Cochrane Central Register of Controlled Clinical Trials 2007, Issue 1. Additional searches were carried out using these websites: NHS Centre for Reviews and Dissemination (CRD) — for Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA), Turning Research into Practice (TRIP), and National Institute for Health and Clinical Excellence (NICE). We also searched for retractions of studies included in the Review. Abstracts of the studies retrieved from the initial search were assessed by an information specialist. Selected studies were then sent to the author for additional assessment, using pre-determined criteria to identify relevant studies.Study design criteria for inclusion in this review were: published systematic reviews, RCTs and prospective and retrospective cohort studies in any language, at least single blinded, and containing more than 20 individuals of whom more than 80% were followed up. There was no minimum length of follow up required to include studies. We excluded all studies described as "open", "open label", or not blinded unless blinding was impossible. In addition we use a regular surveillance protocol to capture harms alerts from organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA), which are added to the reviews as required. We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table ).

Table
GRADE evaluation of interventions for Mammalian bites

Glossary

Abrasion
The scraping or rubbing away of a small area of skin or mucous membrane.
Avulsion
A wound resulting from the ripping or tearing away of a part.
Debridement
The removal of crushed, dirty, or devitalised tissue from a wound.
Laceration
Occurs when the skin, soft tissues, or both are torn by the crushing and shearing forces produced on impact; characterised by ragged, irregular margins, surrounding contusion, marginal abrasion, and tissue bridging in the wound depths. Uncomplicated lacerations are linear, not contaminated by dirt, with no devitalisation of the wound edges, and present to the physician within a few hours of occurrence.
Low-quality evidence
Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Primary wound closure
The closing or suturing of a wound at the time of initial inspection by a healthcare provider.
Puncture
A wound caused by perforation of the skin with a sharp point.
Very low-quality evidence
Any estimate of effect is very uncertain.

Notes

Disclaimer

The information contained in this publication is intended for medical professionals. Categories presented in Clinical Evidence indicate a judgement about the strength of the evidence available to our contributors prior to publication and the relevant importance of benefit and harms. We rely on our contributors to confirm the accuracy of the information presented and to adhere to describe accepted practices. Readers should be aware that professionals in the field may have different opinions. Because of this and regular advances in medical research we strongly recommend that readers' independently verify specified treatments and drugs including manufacturers' guidance. Also, the categories do not indicate whether a particular treatment is generally appropriate or whether it is suitable for a particular individual. Ultimately it is the readers' responsibility to make their own professional judgements, so to appropriately advise and treat their patients.To the fullest extent permitted by law, BMJ Publishing Group Limited and its editors are not responsible for any losses, injury or damage caused to any person or property (including under contract, by negligence, products liability or otherwise) whether they be direct or indirect, special, incidental or consequential, resulting from the application of the information in this publication.

References

1. Dire DJ. Emergency management of dog and cat bite wounds. Emerg Med Clin North Am 1992;10:719–736. [PubMed]
2. Goldstein EJ. Bite wounds and infection. Clin Infect Dis 1992;14:633–638. [PubMed]
3. Medeiros I, Saconato H. Antibiotic prophylaxis for mammalian bites (Cochrane Review). In: The Cochrane Library, Issue 3, 2005. Chichester, UK: John Wiley & Sons, Ltd. Search date 2001; primary sources Medline, Embase, Lilacs, the Cochrane Controlled Trials Register, and hand searches of Brazilian Infectious Diseases Meetings (1980–1995).
4. Overall KL, Love M. Dog bites to humans — demography, epidemiology, injury and risk. JAMA 2001;218:1923–1934. [PubMed]
5. Sacks JJ, Kresnow M, Houston B. Dog bites: how big a problem? Inj Prev 1996;2:52–54. [PMC free article] [PubMed]
6. Quinlan KP, Sacks JJ. Hospitalizations for dog bite injuries. JAMA 1999;281:232–233. [PubMed]
7. Fishbein DB, Bernard KW. Rabies virus. In: Mandell, Douglas and Bennett's principles and practice of infectious diseases. 4th ed. Vol 2:1527–1543. New York, NY: Churchill Livingstone.
8. Broder J, Jerrard D, Olshaker J. Low risk of infection in selected human bites treated without antibiotics. Am J Emerg Med, 2004;22:10–13. [PubMed]
9. Avner JR, Baker MD. Dog bites in urban children. Pedriatrics 1991;88:55–57. [PubMed]
10. Talan DA, Citron DM, Abrahamian FM, et al. Bacteriologic analysis of infected dog and cat bites. Emergency Medicine Animal Bite Infection Study Group. N Engl J Med 1999;340:85–92. [PubMed]
11. Sacks JJ, Sattin RW, Bonzo SE. Dog bite-related fatalities from 1979 through 1988. JAMA 1989;262:1489–1492. [PubMed]
12. Karlson TA. The incidence of facial injuries from dog bites. JAMA 1984;251:3265–3267. [PubMed]
13. Goldstein EJC, Reinhardt JF, Murray PM, et al. Outpatient therapy of bite wounds. Demographic data, bacteriology, and prospective, randomized trial of amoxicillin/clavulanic acid versus penicillin ± dicloxacillin. Int J Dermatol 1987;26:123–127. [PubMed]
14. World Health Organization. WHO Weekly Epidemiological Record, Vol 74 (45), 1999. http://www.who.int/docstore/wer/pdf/1999/wer7445.pdf (last accessed 04 September 2006).
15. Maimaris C, Quinton DN. Dog-bite lacerations: a controlled trial of primary wound closure. Arch Emerg Med 1988;5:156–161. [PMC free article] [PubMed]
2006; 2006: 0914.
Published online 2006 May 1.

Antibiotic prophylaxis for human bites

Summary

INFECTION RATES Antibiotics compared with placebo: We don’t know whether prophylaxis with antibiotics may be more effective at reducing rates of infection in people with human bites compared with placebo ( very low-quality evidence ).

Benefits

Human bites:

We found one systematic review and one subsequent RCT comparing antibiotic use in people following a human bite. The review included one RCT of human bites comparing oral cephalosporin versus intravenous cephalosporin plus penicillin versus placebo. It found that antibiotic prophylaxis by either route significantly reduced the proportion of people with wound infection compared with placebo (48 people with uncomplicated bites on the hand in the preceding 24 hours; 0/33 [0%] with oral or intravenous antibiotic prophylaxis v 7/15 [46.7%] with placebo; P < 0.05; timescale not reported). The subsequent RCT found no significant difference between a cephalexin/penicillin combination and no treatment in rate of infection after 96 hours (127 people attending an emergency department with a low risk human bite [not on hands or feet, or over cartilaginous areas] sustained in the previous 24 hours; rate of infection: 0/63 [0%] with antibiotics v 1/62 [1.6%] with placebo; reported as not significant; P value not reported). None of the people in this study required wound closure or admission for treatment.

Harms

Neither the review nor the subsequent RCT reported on adverse effects.

Comment

Most of the RCTs were small and gave insufficient information about allocation concealment and randomisation. Some studies were not double blind, and four studies had withdrawal rates greater than 10%.

Clinical guide:

Recent articles have called into question the value of treating all mammalian bite wounds that are of low risk of infection with antibiotics. Prophylactic antibiotics should be considered for high risk bites (such as bites on the hand) within 3 hours of the injury. The efficacy of antibiotic prophylaxis for low risk bites or 24 hours after injury remains unclear. For now, the clinician should consider prophylactic antibiotics where there is deep puncture, crushing bites where much devitalised tissue exists, and for overtly dirty bites. Bites that appear to involve simply epidermal stripping, or scratches and abrasions, are not likely to benefit from prophylactic antibiotics.

Substantive changes

Antibiotic prophylaxis: One RCT added; categorisation unchanged (likely to be beneficial).

2006; 2006: 0914.
Published online 2006 May 1.

Antibiotic prophylaxis for non-human bites

Summary

INFECTION RATES Antibiotics compared with placebo: Prophylaxis with antibiotics may be no more effective at reducing rates of infection in people with mammalian bites compared with placebo ( very low-quality evidence ).

Benefits

We found one systematic review, which compared prophylactic antibiotics versus placebo or no treatment. There was significant heterogeneity between trials. The review found no significant difference in infection rate with antibiotic prophylaxis compared with placebo after dog, cat, or human bites (search date 2001; 7 RCTs and 1 quasi-randomised controlled trial; 522 people bitten by dogs, cats, or humans in the preceding 24 hours; OR of infection 0.49, 95% CI 0.15 to 1.58; timescale not reported). When the results were analysed for each wound site (hands, trunk, arms, or head/neck), antibiotic prophylaxis significantly reduced infections of the hand only (3 RCTs: 2% with antibiotic prophylaxis v 28% with control; OR 0.10, 95% CI 0.01 to 0.86; NNT 4, 95% CI 2 to 50). The review found no significant effect of wound type (lacerations, puncture, or avulsions) on efficacy of antibiotics in preventing infection compared with control groups (puncture lesions, 2 RCTs, 30 people: OR 0.22, 95% CI 0.05 to 13.67; lacerations, 2 RCTs, 129 people: OR 0.80, 95% CI 0.05 to 13.67; avulsion wounds, 2 RCTs, 71 people: OR 1.07, 95% CI 0.11 to 10.63).The review found no significant difference in infection rate with antibiotic prophylaxis compared with control in people who had been bitten by dogs (6 RCTs, 463 people, infection rate: 10/225 [4.4%] with antibiotic prophylaxis v 13/238 [5.5%] with control; OR 0.74, 95% CI 0.30 to 1.85). The review identified one small RCT of cat bites (12 people), which found no significant difference in infection rate with antibiotic prophylaxis compared with control (0/5 [0%] with antibiotic prophylaxis v 4/6 [66.7%] with control; P less than 0.06). There is no further description of wound severity in this review.

Harms

The systematic review did not report on adverse effects.

Comment

Most of the RCTs reported by the review were small and gave insufficient information about allocation concealment and randomisation. Some studies were not double blind, and four studies had withdrawal rates greater than 10%.

Clinical guide:

Recent articles have called into question the value of treating all mammalian bite wounds that are of low risk of infection with antibiotics. Prophylactic antibiotics should be considered for high risk bites (such as bites on the hand) within 3 hours of the injury. The efficacy of antibiotic prophylaxis for low risk bites or 24 hours after injury remains unclear. For now, the clinician should consider prophylactic antibiotics where there is deep puncture, crushing bites where much devitalised tissue exists, and for overtly dirty bites. Bites that appear to involve simply epidermal stripping, or scratches and abrasions, are not likely to benefit from prophylactic antibiotics.

Substantive changes

2006; 2006: 0914.
Published online 2006 May 1.

Debridement, irrigation, and decontamination

Summary

We found no clinically important results assessing debridement, irrigation, decontamination measures, or infiltration of serum into the wound in the treatment of people with bites. However, there is consensus that such measures are likely to be beneficial.

Benefits

We found no systematic review, RCTs, or good cohort studies.

Harms

We found no evidence.

Comment

Clinical guide:

It would be regarded as unethical to conduct an RCT comparing debridement, irrigation, and decontamination versus no treatment, because there is consensus that such measures are likely to be beneficial. Copious irrigation with saline (minimum amount of 1 L) has become standard.

Substantive changes

No new evidence

2006; 2006: 0914.
Published online 2006 May 1.

Immunisation against tetanus

Summary

We found no direct information about the effects of tetanus toxoid or tetanus immunoglobulin in preventing tetanus in people after human or animal bites. There is clinical consensus that tetanus immunisation should be given routinely as part of wound care for mammalian bites.

Benefits

Tetanus toxoid:

We found no systematic reviews, RCTs, or cohort studies (see comment below).

Tetanus immunoglobulin:

We found no systematic reviews, RCTs, or cohort studies (see comment below).

Harms

We found no evidence.

Comment

Clinical guide:

Immunisation against tetanus using tetanus toxoid is routinely given as part of wound care for bites. Therefore, an RCT comparing tetanus immunisation versus no immunisation would be considered unethical. It is difficult to assess whether a mammalian bite wound is any more tetanus prone than that of a non-bite laceration; both may be colonised with Clostridium tetani spores, although this is not a reliable indicator as to whether tetanus will develop. As with the care of any wounds, people with mammalian bites should be assessed for tetanus immunisation status, and immunised if they do not have current anti-tetanus coverage. Because bites are considered to be “dirty”, if there is no record of tetanus vaccination in the previous 5 years, administration of the vaccine on the day of presentation is called for.

Substantive changes

Immunisation against tetanus: Evidence reassessed; recategorised as likely to be beneficial based on consensus.

2006; 2006: 0914.
Published online 2006 May 1.

Primary wound closure

Summary

INFECTION RATES Primary wound closure compared with no closure: Primary closure of a wound in people with dog bites may be no more effective at reducing infections compared with no wound closure ( low-quality evidence ). NOTE There is consensus that primary closure of most bite wounds is likely to be beneficial and does not increase the risk of subsequent infection.

Benefits

We found no systematic review. We found one RCT comparing primary wound closure versus no closure.The trial excluded wounds that were infected at presentation, required plastic surgery, or involved other structures such as nerve, tendon, joint, or bone. All wounds were debrided and irrigated, and tetanus immunisation was updated, but no antibiotic prophylaxis was given. In uncomplicated lacerations, closure was performed by an experienced nurse; in complicated lacerations, closure was performed by a specialist physician. The RCT found no significant difference in the incidence of infection with closed compared with open wounds (96 people bitten by dogs in the preceding 24 hours; incidence of infection: 7/92 [7.6%] with closed v 6/77 [7.8%] with open; RR 0.98, 95% CI 0.33 to 2.62; timescale not reported). There were significantly more infections of the hand compared with the rest of the body (69% v 31%), but there was no difference between closure and non-closure groups in the rate of hand infection (5/9 [55.6%] with closure v 4/9 [44.4%] with non-closure).

Harms

The RCT did not report on adverse effects.

Comment

Although the RCT found no increased risk of infection with primary wound closure, further RCTs are required to confirm this conclusion, and also to evaluate if wound closure of bites from a rabid animal may increase the risk of rabies. Wound morphology was poorly described in this study.

Clinical guide:

Although evidence is limited in this arena, it has long been thought that primary closure of most bite wounds is likely to be beneficial and does not increase the risk of subsequent infection. The clinician should practice good wound care, including copious irrigation and debridement of devitalised tissue, as necessary, prior to closure. The wound should be re-examined 1–2 days after initial visit.

Substantive changes

No new evidence

2006; 2006: 0914.
Published online 2006 May 1.

Antibiotics for treating infected bites

Summary

We found no direct information from RCTs about whether antibiotics are better than no active treatment for infected mammalian bites. However, there is consensus that antibiotics are likely to be beneficial.

Benefits

Antibiotics versus placebo:

We found no systematic review or RCTs.

Harms

We found no evidence. See harms under comparative effectiveness of different antibiotics.

Comment

None.

Clinical guide:

Evidence on the efficacy of antibiotics for the treatment of infected mammalian bites is limited. Selection of appropriate antibiotics should take into account the mouth flora of the biting animal and human skin flora of the recipient.

Substantive changes

No new evidence

2006; 2006: 0914.
Published online 2006 May 1.

Comparative effectiveness of different antibiotics

Summary

TREATMENT FAILURE Penicillin (with or without dicloxaxillin) compared with amoxicillin/clavulanic acid: Penicillin (with or without dicloxaxillin) may be no more effective at reducing failure rates in people with infected and uninfected animal and human bites compared with amoxicillin /clavulanic acid ( very low-quality evidence ).

Benefits

Comparison of different antibiotics:

We found no systematic reviews but found one RCT comparing penicillin plus or without dicloxacillin versus amoxicillin (amoxycillin)/clavulanic acid. Treatment was given for 5 days in people bitten less than 8 hours previously or in those without clinical infection (34 people), and for 10 days in people bitten more than 8 hours previously or with clinical infection (27 people). All wounds received usual care and were left closed or open at the discretion of the attending physician.The RCT found no significant difference in failure rate (which was undefined) with penicillin/dicloxacillin compared with amoxicillin (amoxycillin)/clavulanic acid (61 people bitten in the preceding 10 days; 48 by animals, 13 by humans; failure rate: 1/31 [3%] with penicillin/dicloxacillin v 3/30 [10%] with amoxicillin (amoxycillin)/clavulanic acid; RR 0.32, 95% CI 0.03 to 2.54; timescale not reported). The RCT did not include a description of bite severity.

Harms

Adverse effects were significantly more common in people using amoxicillin (amoxycillin)/clavulanic acid compared with penicillin/dicloxacillin (3/30 [10.0%] with penicillin/dicloxacillin v 13/31 [41.9%] with amoxicillin (amoxycillin)/clavulanic acid; RR 4.2, 95% CI 1.5 to 7.4; NNH 3, 95% CI 2 to 19). Diarrhoea was the most common adverse event (1/30 [3.3%] with penicillin/dicloxacillin v 9/31 [29.0%] with amoxicillin (amoxycillin)/clavulanic acid; RR 8.71, 95% CI 1.34 to 23.3; NNH 4, 95% CI 1 to 79).

Comment

Interpretation of the results of the RCT is difficult because the main outcome measure of “failure rate” was not defined. Also, failure rates were not separated according to whether people had infected or uninfected wounds at inclusion. We found no RCTs comparing antibiotics versus placebo for infected mammalian bites; however, there is consensus that they are likely to be beneficial.

Clinical guide:

Evidence on the efficacy of antibiotics for the treatment of infected mammalian bites is limited. Selection of appropriate antibiotics should take into account the mouth flora of the biting animal and human skin flora of the recipient.

Substantive changes

No new evidence


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