Prevention of post-operative infections after surgical treatment of bite wounds.

After reviewing the literature about the microbial spectrum, the risk factors of post-operative infections, and the results of surgical interventions, the following recommendation can be made for the management of bite wounds:FRESH, OPEN WOUNDS: surgical debridement, if appropriate, then an antiseptic lavage with a fluid consisting of povidone iodine and ethanol (e.g., Betaseptic(®)), no antibiotics, primary wound closurenearly closed fresh wounds (e.g., cat bites): surgical debridement, if appropriate, dressing with an antiseptic-soaked compress for ~60 minutes with repeated soaking (e.g., Betaseptic(®)), no antibioticsolder wounds after ~4 hours: surgical debridement, if appropriate, dressing with an antiseptic-soaked compress or bandage for ~60 minutes with repeated soaking (e.g., Betaseptic(®)), at the same time intravenous or dose-adapted oral antibiotics (Amoxicillin and/or clavulanic acid)older wounds after ~24 hours: surgical debridement, then antiseptic lavage (Betaseptic(®)), in case of clinically apparent infection or inflammation surgical revision with opening of wound and treatment with antibiotics according to resistogram (empirical start with Amoxicillin and/or clavulanic acid).For each kind of bite wound, the patient's tetanus immunization status as well as the risk of exposure to rabies have to be assessed. Similarly, the possibility of other infections, such as lues (Syphilis), hepatitis B (HBV), hepatitis C (HBC), hepatitis D (HDV) and HIV, in the rare case of a human bite wound, has to be taken into account.

Introduction

Compared to the incidence of bite wounds by dogs or cats, human bite wounds are very rare [1]. Approximately 60–80% of all bite wounds are caused by dogs and 20–30% by cats. Bite wounds caused by humans are very rare in rural areas, but in urban regions, they may account for up to 20% [2]. While the contagion with zoonotic diseases caused by animal bites, such as rabies, cat scratch disease, cat pox, rat-bite fever, tularaemia, brucellosis, leptospirosis, and tetanus, which might also be caused by an incident-related trauma, have become rare, the oral flora of humans contains agents which can cause severely progressing wound infections, possibly leading to disseminated infections and sepsis. The oral flora of animals and humans is characterized by complex bacterial populations of more than 1,000 different species. However, only a few strains of bacteria are isolated in the wound when treating bite wounds, which is partly due to selective diagnostic methods. Wound infections of cat and dog bites are, therefore, often found to be caused by Pasteurella canis, Pasteurella multocida, or Mannheimia haemolytica, whereas Staphylococcus aureus, Streptococcus pyogenes, Capnocytophaga canimorsus, Neisseria and Moraxella spp. are more rare [3], [4], [5].

Anaerobes were found in 39% of animal bite wounds and in 50% of human bite wounds [6]. Frequently occurring anaerobes are Bacteroides, Fusobacterium, Peptococcus, Veillonella, Porphyromonas und Prevotella spp. [4]. Both wound and systemic infections caused by human bites are found to be caused by Eikenella corrodens, β-lactamase-resistant anaerobes, ESBL and MRSA [3]. A possible infection with hepatitis B [7], [8], [9], [10] and C [11], [12], HIV [13], [14] and syphilis [15], [16] must also be considered, although these incidents are very rare. Cat bite wounds are more often accompanied by an infection than dog bite wounds due to the deeper tooth puncture and subsequent inoculation with bacteria [17]. The risk of infection after human bites was ≥20% [18] depending on location of the wound; after dog bites, the risk ranged between 3% and 17% [19].

Because the prevention of a wound infection cannot initially be accompanied by pathogen testing, the risk of infection must be minimized by surgical treatment in conjunction with antiseptic techniques and antibiotics, if appropriate.

The first signs of a wound infection often develop within the first 24 hours after injury; if there are no signs after 72 hours, no infection is to be expected. Local symptoms, such as redness, swelling, and feelings of tension are rarely accompanied by general symptoms, e.g., fever. Isolated incidents may include sepsis and signs of disseminated intravascular coagulation [20]. Chronic infections such as osteitis and osteomyelitis can develop by direct infiltration of pathogens through the periosteum or per continuitatem from soft tissue infections [21].

In Germany, there is no recommended standard treatment for bite wounds, although incidence rates range from 30,000 to 50,000 per year, and approximately 1–2% of emergency treatments are due to these kinds of injuries [21]. The main reason for this is a lack of comprehensive and well-conceived research in this area. Therefore, it is the aim of this study to condense the existing scientific and medical knowledge into recommendations for the prevention of post-operative infections of surgically treated bite wounds.

Risk factors for post-operative wound infections

The risk of infection for bite wounds of the hand is particularly high, because very often bradytrophic tissue is involved [22]; this also applies to joint injuries. The risk of infection is also significantly higher for wounds requiring surgical debridement, for patients older than 50 years of age [23], and for wounds treated ≥12 hours after injury [18].

Cat bite wounds are frequently underestimated, because they present with a seemingly harmless puncture which often closes within hours. Problems may arise, however, from persisting and proliferating bacteria under the closing skin, which may cause a deep soft tissue infection [24].

Treatment of dog bite wounds presents other complications, because besides the bacterial contamination, there are contusions, cuts, and lacerations which might lead to haematoma, delayed skin necrosis, or demarcations [25].

Diagnostics and documentation

Bite wounds need to be examined carefully. Secondary injuries to nerves, blood vessels, tendons, and bones, as well as ischemia must be ruled out. Depending on the extent and the location of the injury, the patient should undergo radiological diagnostics to make sure no foreign bodies (teeth, food) remain in the wound and to investigate possible bone injuries, particularly relevant for the detection of cranial injuries in a child. Anamnesis and initial treatment of a bite wound should take place within an appropriate clinical setting, if necessary under general anaesthesia, because the quality of the primary treatment determines the functional and aesthetic outcome.

The soft tissue around a bite wound should be investigated carefully to give a realistic assessment of the surface area and depth of the wound. A precise, detailed case history should be written down, and, better still, a photographic record should be compiled, because bite wounds and their treatment may have legal consequences.

Debridement and plastic surgery

Open bite wounds (e.g., dog bite) should be treated with surgical debridement, during which only avital wound edges should be sparingly excised, particularly when the injury involves hands, feet, or face. Here, the aim should be to preserve as much tissue as possible and to excise avital tissue only [26]. Surgically treated wounds must be examined on the second and third post-operative day. In case of phlegmones and abscesses, debridement must be repeated and the patient treated with antiseptic agents or, if necessary, antibiotics. While some authors favor the replantation of severed organ or tissue parts for head injuries, others prefer primary plastic reconstruction [21], [27].

Injured hands, arms and legs are to be placed in an immobile and, if possible, elevated position. If extensive injuries to the face, or other critical bite wounds, have been sustained, the patient should be hospitalized for observation after primary treatment of the wounds.

Antiseptic wound treatment

In treating bite wounds, fresh injuries of ≥4 hours post-bite have to be distinguished from those of ≥24 hours post-bite. At the same time, the degree of access for antiseptic agents must be considered.

Fresh, open bite wounds

After a possibly necessary debridement, the wound must be rinsed with an antiseptic agent. The agent of choice should be a mixture of povidone iodine and ethanol (e.g., Betaseptic®), because both the alcohol and the iodine penetrate into the tissue quickly and can take effect [28], [29], [30], [31]. However, solvents containing alcohol may cause severe burning sensations when applied, and therefore sensitive patients (e.g., children) might require local anesthesia. Should the patient suffer from thyroid gland dysfunction or a known iodine allergy, an ethanol-based skin antiseptic, such as AHD 2000, may be an alternative.

Fresh, nearly closed bite wounds (e.g., cat bite)

These should be dressed with an antiseptic-soaked compress for ~60 minutes with repeated soaking (Betaseptic®, but if that is contra-indicated, AHD 2000 may be applied). The administration of antibiotics is not necessary. If the antiseptic has no access to the wound (e.g., cat bite through fingernail), a one-time administration of antibiotics is indicated (Amoxicillin and/or clavulanic acid).

When selecting an antiseptic, the following should be noted:

Surface antiseptics such as octenidine, polihexanide or chlorhexidine may theoretically aid decontamination of the wound due to their surface tension, but in comparison to alcohol and povidone iodine, which are systemically absorbed, it is unlikely that they have an effect on deeper wounds [32]; this hypothesis is supported by their lack of absorption when applied to surface wounds [33], [34], [35].

Infiltration of octenidine with pressure into deep soft tissue is contra-indicated, because one such application to the stab wound of a child’s hand resulted in severe, long-term side effects with edema and tissue damage [36]. Lavage of deep wounds, such as bite injuries, is permitted only when the rinsing solution can be adequately drained.

Older bite wounds after ~4 hours

Depending on the kind of injury, a surgical debridement must be performed before an antiseptic agent is applied. Because the agent should be infiltrated into the wound, it should be dressed with a compress or bandage soaked in an antiseptic for ~60 minutes with repeated soaking (Betaseptic®, but if that is contra-indicated, AHD 2000 may be applied). We would recommend a one-time simultaneous administration of intravenous antibiotics. Although this has not been verified by studies, this step seems sensible to combat proliferating pathogens which are not accessible for the antiseptic due to early abscess formation.

Older bite wounds after ~24 hours

Depending on the kind of injury, a surgical debridement should be performed before the wound is rinsed with an antiseptic. Should an infection or inflammation be clinically apparent, a surgical revision with an opening of the wound is indicated, before the wound is rinsed again with an antiseptic and antibiotics are given.

Tetanus prophylaxis

The patient’s immunization status must be carefully assessed. Should this prove difficult, it should be assumed that the patient is not sufficiently protected and should be actively and passively vaccinated. This procedure also applies if the patient’s medical history shows only one previous vaccination. If there is evidence of two previous vaccinations, only one more vaccination is needed, but only if the injury happened no longer than 24 hours ago. If there is evidence of three previous vaccinations dating back to more than five years ago, no further immunization is need [37].

Exclusion of rabies

In Germany, the number of people contracting rabies is very low. However, besides the more widely known source of infection, i.e., bite wounds by wild animals, bite wounds by cats and dogs are the most likely source of human infections.

If unknown, the immunization status of the animal causing the wound should be investigated whenever possible. In addition, the laws for dealing with rabies must be followed [38], i.e., dogs and cats suspected of being infected with rabies may be ordered by the authorities to be put down or, in certain cases, they may be quarantined for a minimum of three months. Vaccinated pets are subject to observation by the authorities.

Depending on the extent of exposure to a wild animal or pet suspected of or being infected with rabies, the following post-exposure measures should be followed [37]:

licking of unbroken skin – no vaccination

nibbling on uncovered skin; superficial, non-bleeding scratches by animal; licking of broken skin – vaccination

any bite or scratch wounds, contamination of mucous membranes with saliva (e.g., by licking, spatters) – vaccination and a one-time simultaneous passive immunization with rabies immunoglobulin (20 IE/kg KM); as much as possible of this dose should be infiltrated in and around the wound, with the remainder being given by deep intramuscular injection.

Immediate decontamination and antiseptic treatment of any bite wound caused by animals is not limited to suspected cases of rabies. The physical and chemical cleansing of the wound is designed to reduce the probability of the virus spreading and proliferating from the wound into muscle cells. The subsequent vaccinations and doses of rabies immunoglobulin are to be carefully recorded. Should patients who have previously received post-exposure vaccines require re-vaccination, the manufacturer’s instructions are to be followed [37].

In cases of severe wounds, human rabies immunoglobulin should be administered simultaneously; the dose should not exceed 20 IE/kg BM. If the patient’s anatomy allows, half of that dose should be infiltrated in and around the wound, the remainder should being given by deep intramuscular injection, preferably in the gluteal muscle. Patients who have received post-exposure vaccines previously have no need for human rabies immunoglobulin.

Prevention of HBV, HCV, HDV and HIV

In the rare case of a human bite wound, the risk of infection with HBV, HCV, HDV and HIV may be assessed by investigating the social environment of the biting person. If possible, every effort should be made to establish the infectious status of that person by drawing and analyzing a blood sample (HIV rapid antibody test, antibody test for HBV, HCV and HDV). To prevent an infection with HIV, the recommendations for post-exposure prophylaxis [39] are not really applicable, because the two most important measures – stimulation or forcing of acute bleeding and antiseptic treatment immediately after injury – are difficult to accomplish. An infection may be expected to have been prevented if the bite wound is treated within 12 hours of injury, i.e., if it is surgically opened, rinsed with an antiseptic, and dressed with a compress repeatedly soaked with the agent (e.g., Betaseptic®). If there is a high probability of infection, post-exposure prophylaxis with systemic drugs should be considered. Ideally, the drug therapy should begin within two hours, but no later than 24 hours after injury. If exposure to HIV is probable, initial drug therapy should combine the three antiretroviral agents Tenofovir, Emtricitabine, and Lopinavir [39]. If the patient’s HBV immunization status is insufficient, he/she should be actively and passively vaccinated with HB immunoglobuline (0.06 ml/kg KM) within 6 hours, if possible, but no later than 24 hours after injury. An antibody titer of >100 IU/l indicates that the patient is adequately protected. If the patient has an antibody titer of <100 IU/l, one vaccination is sufficient. In case of a probable infection with HCV, it is recommended that the patient should be treated with Ribavirin (3 capsules of 200 mg twice daily p.o.) and PEGylated interferon-alpha (3 mill. units once a week i.v. for 3–8 months depending on the quantity of HC viruses and the level of ALAT) to avoid chronification. Each incidence of injury caused by a human bite should be immediately followed by an antibody test to rule out infections with HBV, HCV, HDV, or HIV from the beginning. This test should be repeated after 6, 12, and 24 weeks.

Antibiotic prophylaxis

Importance

The routine administration of antibiotics in treating bite wounds has only little [40] to no effect [41], [42]. This also applies to hand injuries [41]. In cases of primary wound closure, antibiotics have no effect on the rate of infection [19]. For injuries which are particularly prone to infections (e.g., very large wounds, extensive haematoma), some authors recommend the prophylactic administration of antibiotics [26]. In all other cases, antibiotics should only be given if the wound shows signs of infection [22].

Selection

Before selecting an antibiotic, the pathogens of the oral flora of the biting mammal as well as the skin flora of the patient must be assessed. In cases of dog or cat bites, at least the following species should be covered by the antibiotic: Pasteurella multocida, Staphylococcus aureus and anaerobes, as well as Capnocytophaga canimorsus, particularly if the patient is immune deficient. When presented with human bite wounds, Gram-positive and anaerobe bacteria, particularly Eikenella corrodens, should be counteracted.

Previous experience suggests that Amoxicillin/clavulanic acid is the antibiotic of choice, because it is effective against most pathogens contracted through bite wounds, including Capnocytophaga canimorsus, as well as against pathogens on the patient’s skin. Other effective antibiotics are also first- and third-generation cephalosporines or Ampicillin [43]. Should the patient be allergic to penicillin, a combination of fluoroquinolones and clindamycin should be administered.

Indication

For fresh bite wounds, no antibiotics are needed. For older bite wounds, approximately 4 hours after injury, a one-time administration of intravenous or dose-adapted oral antibiotics is indicated. For bite wounds sustained more than 24 hours ago, prophylaxis with an antibiotic makes no sense, because symptoms of an infection usually develop within the first 24 hours after injury.

Some authors recommend antibiotic prophylaxis after cat bite injuries due to the higher risk of infection [26], [44], although an antiseptic treatment, properly performed, seems to cast doubt on the efficacy of additional prophylaxis. A Cochrane analysis revealed no added advantage to this procedure [45]. The same study found an advantage to antibiotic prophylaxis after a human bite, but this needs to be investigated further [45].

Should a bite wound present with a clinically apparent infection, e.g., a phlegmonous inflammation, surgical revision with debridement and opening of the abscess is indicated [26]. Further treatment with antibiotics according to a resistogram or according to the sequence as described above, should follow.

Wound closure

Small wounds such as abrasions and lacerations do not require surgical suturing [46], and it is generally understood that primary closure of bite wounds to the face and head is the standard course of treatment [40], [27]. There is also an increasing understanding that delayed closure of bite wounds in other parts of the body should only be considered when treating already infected wounds or wounds prone to infection [3], [47], because surgical treatment in conjunction with antiseptic techniques define the outcome to a considerable degree. After primary closure, the healing process is accelerated and the esthetic outcome improved. Primary wound closure can be performed within the first 12 hours after surgical and antiseptic treatment as well as a one-time antibiotic prophylaxis, if appropriate [21]. Even infected wounds can be closed if an adequate drain is put in place. A prospective, randomized trial analyzing the treatment of lacerated dog bite wounds, of which 92 were closed and 77 remained open, revealed no significant difference in infection rates [48].

Conclusion

After analyzing the existing literature, the following measures for the management of bite wounds are recommended:

Fresh injuries

Open: If the bite wound is easily accessible, surgical debridement should be performed if appropriate, followed by an antiseptic lavage; no antibiotics; primary closure.

Nearly closed (e.g., cat bite, sting by pike fin): Surgical debridement, if appropriate, dressing with an antiseptic-soaked compress for ~60 minutes with repeated soaking; no antibiotics.

Injuries after 4 hours

Surgical debridement if appropriate, dressing with an antiseptic-soaked compress or bandage for ~60 minutes with repeated soaking, simultaneously one-time intravenous or dose-adapted oral antibiotics.

Injuries after 24 hours

Surgical debridement if appropriate, then antiseptic lavage; in case of clinically apparent infection or inflammation, surgical revision with opening of wound and treatment with antibiotics according to resistogram.

Each bite wound requires that the patient’s tetanus immunization status and the risk of exposure to rabies be investigated. The same applies to possible risks of infections with HBV, HCV, HDV and HIV.