Advertisement
Feature Article

Human and animal bites: managing and preventing infection

STEPHEN MUHI, JUSTIN DENHOLM
OPEN ACCESS

Assessment and management

Steps in the assessment and management of human and animal bite wounds are discussed below and summarised in Box 2

Initial management

All recipients of bite injuries should be assessed for haemodynamic instability and penetrating traumatic injuries should be managed emergently, with a focus on haemorrhage control with direct pressure and assessment of neurovascular supply to distal structures. Even apparently minor injuries may cause deep penetration (e.g. cat bites) and may need exploration, which also aids in identifying foreign bodies or broken animal teeth.

Musculoskeletal injuries should be assessed with radiography for bony injury or foreign bodies, and clinical assessment (e.g. joint range of motion) with ultrasonography for injuries involving joints, deep ligaments or tendons. Patients with these injuries should be referred for surgical assessment and repair.

Wound care

Meticulous wound care includes cleaning the surface and flushing the injury for 15 minutes with soap and water, or povidone iodine if available,13 and physical removal of major contamination. Vigorous irrigation and debridement should be performed to reduce the concentration of bacteria. Elevating the injury and applying an ice pack may provide analgesia and reduce swelling.13

Advertisement
Advertisement

Wound closure

The subject of primary closure, delayed closure or healing by secondary intention is controversial, as evidence is limited and recommendations differ.13 Indications for primary closure include bite wounds where cosmesis is important (especially the face). Bite wound infection of the head and neck is less common, likely due to the excellent blood supply and lack of dependent oedema. Wounds at high risk of infection should not be closed by primary closure.13,69

Use of prophylactic antibiotics

Patients with wounds at high risk of ­infection require prophylactic antibiotics. Such wounds include:9,13

  • crush injuries
  • puncture wounds, especially from cat and human bites
  • wounds overlying bone, joints, tendons and prostheses
  • wounds in patients whose presentation is delayed more than eight hours
  • wounds on the hands and feet
  • wounds in immunocompromised hosts (including those with anatomical and functional asplenia)
  • wounds in areas of venous or lymphatic compromise (e.g. lymphoedema, diabetic feet).

Treatment of infected wounds

Gram stain, culture and sensitivity testing guide subsequent antibiotic therapy; ­however, there is no need to take wound cultures unless the wound appears clinically infected. Clinical signs of infection include fever, erythema, oedema, wound discharge and surrounding lymphangitis. It is prudent to obtain blood cultures (for both aerobic and anaerobic organisms) and wound cultures before antibiotics are started. Full blood count and inflammatory markers (e.g. C-reactive protein level) should also be measured. Surgical consultation of patients is often required to consider debridement, exploration to assess involvement of underlying structures, abscess drainage and removal of suture material, if present.

Advertisement
Advertisement

Recommended antibiotics for empirical therapy of bite wound infections are listed in Table 1 and Table 2. Patients with complex infections that involve deeper structures, such as tenosynovitis, septic arthritis and osteomyelitis, require treatment for prolonged durations (usually with an initial parenteral course for two to four weeks, depending on the structure involved and duration of infection),9 and infectious diseases specialist referral is recommended. Cases involving infected wounds that respond poorly to empirical antibiotics or patients with multiple allergies or drug intolerances should also be discussed with an infectious diseases physician.

Tetanus prophylaxis

Tetanus is caused by the neurotoxin produced by Clostridium tetani, leading to tetanic contractions, myotonia and trismus. It is rare in Australia, with 156 hospitalisations between 2001 and 2006 and three deaths (case fatality rate, about 2%). In addition to animal bites, human bites have also been reported to transmit tetanus.70 Tetanus vaccination is only available in combination with other agents (such as diphtheria, tetanus, acellular pertussis; DTPa), and given as a three-dose primary schedule at 2, 4 and 6 months of age.47 ­Tetanus may occur even after apparently trivial wounds, although bites are categorised as tetanus-prone wounds requiring assessment for tetanus vaccination (Table 3).

Pages

Dr Muhi is an Infectious Diseases Registrar at the Victorian Infectious Diseases Service, Royal Melbourne Hospital. Associate Professor Denholm is Medical Director of the Victorian Tuberculosis Program; Senior Staff Specialist at the Victorian Infectious Diseases Service, Royal Melbourne Hospital; and Principal Research Fellow in the Department of Microbiology and Immunology, University of Melbourne, Melbourne, Vic.