Antibiotics: Take a bite out of resistance

Published in MedicineWise News

Date published: About this date

Clinical content may change after this date. This information is not intended as a substitute for medical advice from a qualified health professional. Health professionals should rely on their own expertise and enquiries when providing medical advice or treatment.

Key points

  • Assess the risk of infection based on patient history.
  • Be aware that human bites are much more likely to become infected than other animal bites.
  • Avoid prophylactic antibiotics unless the wound/patient has a high infection risk.
  • Cleaning, debridement, irrigation, elevation and immobilisation are the recommended first-line management for bite and clenched fist injuries

Antibiotic use in Australia is high and growing

Australian health professionals continue to prescribe higher rates1 and average doses of antibiotics than those in many western European countries.2 In 2013, more than 29 million prescriptions were written for PBS-listed antibiotic medicines according to the latest drug utilisation data.2 This is despite evidence linking greater use of antibiotics to resistance and worse individual outcomes.3

The latest national drug utilisation data show that 75% of antibiotics are prescribed by general practitioners.2 These data include prescribers from a range of health care settings and only reflect antibiotics dispensed on the PBS, including those that may have been prescribed but not dispensed.2 Despite these limitations, the results highlight that Australian GPs are well-placed to address antibiotic resistance.

Resistant strains make choosing antibiotics more difficult

S aureus that is methicillin-resistant (MRSA), and therefore resistant to all β-lactam antibiotics, is widespread, with skin and soft tissue infections among the most common sources. Although most of the data describe the problem in hospital settings, there is an emerging picture of antibiotic resistance in community settings across Australia.

A 2012 survey of community-acquired S aureus found:4

  • the rate of MRSA infections in Australia increased significantly between 2000 and 2012, rising to a national rate of ~18% with the highest rate seen in New South Wales
  • ~ 40% of all MRSA infections were resistant to erythromycin or ciprofloxacin, ~ 15% to tetracycline and 10% to gentamicin or trimethoprim-sulphamethoxazole
  • nearly 18% of methicillin-resistant isolates were from skin and soft tissue.

These survey results illustrate why choosing the appropriate empirical antibiotic for community-acquired S aureus infections is increasingly difficult. Despite recommendations to prescribe narrow spectrum antibiotics wherever possible,5 more than 90% of the penicillin and cephalosporin prescriptions supplied on the PBS in Australia in 2013 were broad or moderate spectrum, while 9% were narrow spectrum.2

Another report on antimicrobial prescribing found that the most common forms of inappropriate prescribing were incorrect duration and choice of antibiotic treatment, as well as issues associated with the dose or frequency of antibiotic therapy.6 While these data reflect prescribing in hospitals, a similar picture would be expected in primary care.

This issue of MedicineWise News focuses on appropriate use of antibiotics for skin and soft tissue injuries with an emphasis on bite and clenched fist injuries.

Assess risk of infection based on patient history

Careful patient assessment, with consideration of each individual’s case history, is essential when managing skin infections. To inform management when there is no established infection, assess the risk of infection before prescribing.

Low-risk skin conditions can be managed without antibiotics

  • Most boils can be treated with incision and drainage without the need for antibiotics.7,8
  • Usually, post-traumatic wounds that are not contaminated can be effectively treated with careful cleaning and debridement, elevation and immobilisation.9
  • In otherwise healthy people with a low risk of infection, most bite and clenched fist injuries can be managed with good wound care alone.10

A closer look at managing bites

In healthy individuals where there is a low risk of infection, bites can typically be managed without prophylactic antibiotic therapy.10 Injuries with a low risk of infection include small wounds that involve no tendons or joints, wounds that present within 8 hours and those that can be adequately debrided and irrigated.10

When assessing risk of infection for bite and clenched fist injuries, consider:

Type of injury11

  • Puncture wounds have higher risk of infection.11,12
  • Clenched fist injuries have higher risk of complications than any other type of bite injuries.13,14

Location of injury11

  • Bites on hands, feet or face are associated with a high risk of infection.10

Quantity and type of bacteria11

  • Human bites have a high infection risk because human saliva carries more types of bacteria in higher concentrations than saliva from other animals.14

Immune status of patient11

  • Immunocompromised patients with bite injuries have a high risk of infections.10

Which bites carry the highest risk?

Click to expand Risk of infection for bite injuries from dogs, cats, humans

Figure 1: Risk of infection for bite injuries from dogs, cats, humans

Dog bites account for about 80% of all reported animal bites,11,15 but, for the most part, dog bites carry the lowest infection risk (see Figure 1). Because cat bites have a higher incidence of deep infection than dog bites, cat bites carry the next highest risk of infection.10,11,16 There is also evidence to suggest that cat bites become infected much more quickly than dog bites.16

Human bites are generally more serious than dog or cat bites.13 They are more likely to have fastidious gram-negative bacteria and anaerobes, some of which are likely β-lactamase producers.10,13 Unfortunately, obtaining a reliable history from patients with ‘fight bites’ can be challenging because these patients are often intoxicated or reluctant to admit the cause of injury.14,17

Are antibiotics overused for injuries from dog bites?

While research on antibiotic use in bite injuries is scarce, a small retrospective audit of treatment for dog bites in one Canberra hospital may suggest some room for improvement.19

Although few dog bites become infected and evidence shows that prophylactic antibiotics are usually not warranted,20,21 a retrospective audit at Canberra Hospital found that 87% of 209 patients treated for dog bites over a 2-year period were prescribed prophylactic antibiotics. 19 The vast majority of patients (95%) presented either on the same day or one day after the bite.

Interestingly, antibiotics were prescribed for all types of wounds, including lacerations and abrasions, and injuries occurring on arms, legs and head. As these types of wounds carry a low risk of infection, the authors suggest that antibiotics may have been ‘used in place of proper wound management’.19

Consider prophylactic antibiotics for injuries with a high risk of infection

Bites on hands have the highest risk of deep damage, severe infection and complications, especially where wounds penetrate tendon sheaths or the mid-palmar space.13 According to a recent systematic review, the strongest evidence for prophylactic antibiotics is for bite wounds on the hand, regardless of whether cats, dogs or humans caused the bite.20

The same study found a reduction in the rate of infection in patients with human bites who presented within 24 hours.20 Prophylactic antibiotics did not appear to reduce the rate of infection after bites by cats or dogs.20

Overall, the evidence for prophylactic antibiotics is weak and the benefits for bites to other parts of the body, or for bites caused by cats or dogs, are less clear.20 The table below presents some features of bite and clenched fist injuries that carry a high risk of infection and may benefit from prophylactic antibiotics, according to guidelines.

High risk bite injuries that may benefit from prophylactic antibiotics10
  • wounds with delayed presentation (8 hours or more)
  • puncture wounds that cannot be debrided adequately
  • wounds on the hands, feet or face
  • wounds involving deeper tissues (eg bones, joints, tendons)
  • wounds in immunocompromised patients

Reduce risk of infection with good wound care

First-line management for all bite and clenched fist injuries includes thorough cleaning, debridement, irrigation, elevation and immobilisation.10 Always check whether tetanus immunisation is up to date.10

In patients with bite wounds who present with an established infection:
Consider delaying primary wound closure10 Although primary closure of bite wounds has better cosmetic outcomes, there is conflicting evidence to suggest it may be associated with higher rates of infection.17,22,23
Collect infected tissue Test for gram stain, aerobic and anaerobic cultures before starting antibiotics.10
Refer to specialist surgeon if wounds are on hands or face Facial and hand wounds have a higher risk of complications.10

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.5

Expert reviewer

Professor John Turnidge, University of Adelaide and Senior Medical Advisor, Australian Commission on Safety and Quality in Health Care

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  2. Drug Utilisation Sub-Committee (DUSC). Antibiotics: PBS/RPBS utilisation 2015. [Online] (accessed 30 August 2015).
  3. World Health Organization. Antimicrobial resistance: Global report on surveillance. Geneva, 2014.
  4. (AGAR) AGoAR. Staphyloccus aureus Programme 2012 Community Survey Antimicrobial Susceptibility Report. 2012. [Online] (accessed 20 October 2015).
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