Human bites: Evaluation and management

INTRODUCTION — The evaluation and management of human bite wounds is discussed here.

Animal bite wounds are discussed separately. (See "Animal bites (dogs, cats, and other mammals): Evaluation and management".)

EPIDEMIOLOGY — It is estimated that 250,000 human bites occur each year in the United States; up to 25 percent of these injuries become infected [1,2]. However, data are limited regarding the true incidence of human bites.

TYPES OF BITES — Human bite wounds can occur because of incidental or purposeful injury [3,4].

Incidental minor bite injuries include "love nips" (to the face, breasts, or genital areas) or self-inflicted wounds (such as paronychia due to nail biting or thumb-sucking) [5,6]. (See "Paronychia".)

Purposeful bites are those in which the biter intended to bite another person or themselves or an injury occurred during a physical altercation between two individuals [7].

The types of bites that cause serious injury or infection include the following:

Occlusal bites — Occlusal bites are frank bites by human teeth. On exam, they appear as semicircular or oval areas of erythema or bruising; the skin may or may not be intact. The most common locations are the fingers, hands, or arms.

Occlusal bites occur most commonly in young children and adult women. In adolescents and adults, occlusal bites to the breasts or genitalia during sexual activity or assault may occur.

In children, occlusal bites typically occur on the face, upper extremities, or trunk as the result of aggressive play with another child; such wounds are often trivial [8]. However, a bite wound on a child may also be due to child abuse, as discussed below. (See 'Obtaining a history' below and 'Physical examination' below.)

Clenched-fist injuries — Clenched-fist injuries ("fight bites") are lacerations from a clenched fist of one person striking the teeth of another (figure 1). They occur most commonly in adolescent boys and adult men [9,10]. The lacerations are small (usually ≤15 mm) and are typically over the third and fourth metacarpophalangeal or proximal interphalangeal joints of the dominant hand.

Skin breaks over the knuckles can lead to the introduction of both skin and oral flora into the joints and fascial layers of the hand [9,10]. Many patients ignore these wounds until the onset of pain, swelling, or purulent discharge; as a result, these injuries are often complicated by established infection at the time patients seek medical attention.

EVALUATION — Following a bite wound, patients may seek care for evaluation of the bite injury itself or for concern of infection.

Obtaining a history — We ascertain the circumstances and location of the bite(s) as well as the patient's symptoms, including any indicators of infection (eg, redness, swelling), alteration in function (eg, decreased range of motion), and neurovascular compromise (eg, weakness, numbness, excessive bleeding).

In addition, we assess the following:

●Source of the bite – Most bites are due to another person. Self-inflicted bites that are intentional may be indicative of underlying psychiatric or other conditions [11-13].

●Events preceding the bite – In adults, physical altercation or sexual activity are the most common sources of purposeful bites. Adults who report a bite wound acquired during sex should be asked whether the sex and the bite were consensual or due to assault. (See "Evaluation and management of adult and adolescent sexual assault victims in the emergency department".)

In children, the most common biter is another child, usually during play but sometimes during an altercation. Bite wounds in children can also be an indicator of abuse by an adult; the physical examination may provide clues to abuse, as described below. (See 'Physical examination' below.)

●Date of last tetanus vaccination

●Presence of bleeding from biter's mouth and human immunodeficiency virus (HIV), hepatitis B, and hepatitis C status, if known – The likelihood of transmission of bloodborne pathogens by a human bite is extremely low, but possible cases have been reported [14-20]. Transmission may be possible if the biter was bleeding from the mouth at the time of the bite and broke the skin of the bitten individual. (See 'Preventing HIV, hepatitis B virus (HBV), and hepatitis C virus (HCV)' below.)

●History of cardiac valve abnormalities or a prosthetic valve – Rarely, Eikenella corrodens (an organism present in human oral flora) causes endocarditis, usually in adults with abnormal or prosthetic heart valves. Intravenous drug use is a more common cause of Eikenella endocarditis than human bites [21]. More information on the microbiology of human bites and Eikenella endocarditis is found below and elsewhere. (See 'Spectrum of antibiotic coverage' below and "Antimicrobial therapy of left-sided native valve endocarditis", section on 'HACEK organisms'.)

Inspecting the wound

Wound preparation — Upon presentation, bite injuries are cleansed to facilitate examination, allow for adequate visualization of the extent of injury, and prevent infection. Appropriate wound management is the most important factor for preventing infection [3].

Initial wound preparation includes the following steps:

●Control bleeding (direct pressure should be applied to actively bleeding wounds).

●Clean wound with soap and water or an antiseptic solution (eg, povidone iodine).

●Irrigate with tap water or sterile saline and remove grossly visible debris (if present).

Cleaning the wound is often better tolerated in patients who present immediately after the bite compared with patients who have an infected wound. For patients with significant pain, local anesthesia may be required to facilitate initial wound care, as discussed separately. (See "Subcutaneous infiltration of local anesthetics" and "Clinical use of topical anesthetics in children".)

Detailed discussion of initial wound preparation is found separately. (See "Minor wound evaluation and preparation for closure".)

Physical examination — Once the wound has been cleaned and bleeding is controlled, examine for the following (see "Minor wound evaluation and preparation for closure", section on 'Evaluation'):

●Proximity of bite to joints, tendons, or bone and potential injury to adjacent structures.

Hand wounds should be carefully examined to assess for damage to the underlying tendon sheath, fascia, joint capsule, and metacarpal head. Wounds over or near the metacarpophalangeal joints should be explored in the relaxed, fingers-extended, and the clenched-fist positions to ensure the wound does not involve tendons or communicate with a fracture or joint (picture 1). (See "Overview of hand infections", section on 'Human bites'.)

●A clenched-fist injury requires evaluation of finger extensor mechanism function (figure 2 and figure 3). (See "Finger and thumb anatomy", section on 'Major joints'.)

Evaluate active and passive extension at the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints. Any limitations of active extension (ie, lack of full extension, "extensor lag") suggests an injury to the underlying structures. An inability to actively extend fully at the MCP but still hold the finger in full extension when passively extended suggests a sagittal band rupture. Evaluate for disruption of the central slip by positioning the PIP in 90-degerees flexion, the MCP and DIP in extension, applying resistance at the middle phalanx, and asking the patient to extent the PIP against that resistance (Elson test); weak extension with a taut, hyperextended DIP suggests central slip injury [4,22].

●Evidence of neurovascular compromise distal to the wound.

●Does the wound break the skin (ie, penetrates the dermis into subcutaneous tissue (figure 4)).

●Retained foreign material (eg, tooth).

●Circumference of the bite marks in children – A mark on a child with maxillary intercanine distance (distance between left and right canine from the outer edge of the tooth) >2.5 cm suggests the bite came from an adult and should raise concern for child abuse (picture 2) [23]. (See "Physical child abuse: Recognition", section on 'Inflicted bruises'.)

●Signs of infection, as discussed immediately below.

Assessing for infection — Infection can cause significant morbidity after human bites. Infection rate ranges from 2 percent for superficial wounds, less than 10 percent for occlusal bites, to over 25 percent for clenched-fist wounds or other hand wounds [2,24,25].

The likelihood of infection after a human bite is determined by the depth and location of the wound and host factors. In most cases, the first signs and symptoms of infection begin approximately 24 hours after the bite, but signs as early as two hours after the bite can occur in some cases [26].

Bite wound infection may be superficial (eg, cellulitis, with or without abscess) or deep (abscess, septic arthritis, osteomyelitis, tenosynovitis, or necrotizing soft tissue infection):

●Signs of superficial infection – Clinical manifestations of cellulitis include tenderness, erythema, swelling, and warmth; purulent drainage, lymphangitis, and/or fever may be present. An associated superficial abscess may present as a tender, erythematous, fluctuant nodule.

●Signs of deep infection – In addition to the above manifestations, clues for deep infection include persistent or progressive pain several days following the initial injury, pain with passive movement, pain out of proportion to exam findings, crepitus, joint swelling, systemic illness (fever, hemodynamic instability), and persistent signs of infection despite initial wound care and antibiotic administration.

The level of suspicion for deep infection should be increased for patients with immunosuppression (including diabetes) or neuropathy; these patients often present later in their course with increased risk of serious infection and limited pain on clinical exam.

A patient with a clenched-fist injury and obvious purulence or significant soft tissue destruction should be presumed to have septic arthritis or osteomyelitis until the wound can be explored, typically in the operating room [27]. A wound with pain, swelling, erythema, or mild drainage but with good, painless joint mobility may not require surgical exploration but should be evaluated by a hand surgeon and may need magnetic resonance (MR) imaging to exclude deep infection.(See "Overview of hand infections", section on 'Human bites'.)

Clinical manifestations of wound infection and associated complications are described further separately. (See "Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis" and "Septic arthritis in adults" and "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis" and "Infectious tenosynovitis" and "Necrotizing soft tissue infections".)

Ancillary tests

Imaging — We obtain plain radiographs in patients with clenched-fist injuries to evaluate for evidence of fracture, joint disruption, or retained foreign body (ie, tooth).

In patients with other types of bites that appear to be clinically uninfected, plain radiographs are typically unnecessary but may be obtained if the bite breaks the skin and bone/joint disruption and/or presence of a foreign body is suspected.

For patients with infected bites, MR imaging may help identify deep infection and tendon injury; ultrasound may help distinguish cellulitis from a drainable abscess. If a joint infection is strongly suspected, imaging may not be required and may delay surgical exposure and direct examination/washout and thus should be made in conjunction with surgical evaluation. (See "Overview of hand infections", section on 'Imaging' and "Imaging techniques for evaluation of the painful joint", section on 'Magnetic resonance imaging' and "Techniques for skin abscess drainage", section on 'Bedside ultrasonography'.)

Cultures (wound, blood)

●Wound cultures – In patients with suspected infection, wound Gram stain and cultures should be obtained to identify the causative pathogen(s) and to guide antibiotic therapy. Specimens should be obtained at the time of debridement (preferably prior to initiation of antibiotics) and samples sent for both aerobic and anaerobic bacterial cultures. The microbiology laboratory should be notified that a human bite wound is the source, so they can use specific techniques to identify fastidious organisms, such as E. corrodens.

In patients with clinically uninfected bite wounds, we do not obtain wound cultures because the results do not correlate with infection [28].

●Blood cultures – We obtain blood cultures in patients with fever or other signs of systemic infection and in immunocompromised patients with any signs of infection [28,29]. Patients who have underlying heart valve abnormalities and signs of systemic infection or endocarditis should have multiple sets of blood cultures and may warrant additional workup, as discussed elsewhere. (See "Clinical manifestations and evaluation of adults with suspected left-sided native valve endocarditis".)

In patients without evidence of systemic infection, the yield of blood cultures is low, and the risk of false positives (eg, skin contamination) typically outweighs the benefit.

Laboratory tests

●Routine bloodwork – In patients with clinically uninfected bite wounds, we do not obtain laboratory tests.

For patients with clinically infected bite wounds, laboratory studies (eg, complete blood count and serum inflammatory markers such as erythrocyte sedimentation rate, C-reactive protein) are reasonable if there is clinical concern for septic arthritis or other serious infection (eg, fasciitis).

●Limited role of HIV, hepatitis B, and hepatitis C testing – The likelihood of bloodborne pathogen transmission for a human bite is extremely low. If the clinical history suggests that transmission is possible, baseline and follow-up testing, as well as prophylaxis, may be indicated, as discussed below and elsewhere. (See 'Preventing HIV, hepatitis B virus (HBV), and hepatitis C virus (HCV)' below and "Management of nonoccupational exposures to HIV and hepatitis B and C in adults".)

MANAGEMENT — Patients may seek care for evaluation of bite injury (in absence of infection) or established bite infection.

Tetanus and bloodborne pathogen prophylaxis — Although the risk is usually low, patients with human bites should undergo evaluation for tetanus or bloodborne pathogen post-exposure prophylaxis.

In addition, human bite wounds may be associated with transmission of viral pathogens including hepatitis B, hepatitis C, HIV, and herpes simplex virus [14-19].

Tetanus prophylaxis — Human bites are considered a tetanus-prone wound. In a fully vaccinated patient (ie, has had ≥3 doses of a tetanus toxoid-containing vaccine), administer a tetanus toxoid-containing vaccine only if their last dose was given ≥5 years ago (or if the date of their most recent vaccine is uncertain) (table 1). In an unvaccinated or partially vaccinated patient, administer a tetanus toxoid-containing vaccine and tetanus immune globulin.

Further details about tetanus vaccination are found separately. (See "Tetanus-diphtheria toxoid vaccination in adults" and "Diphtheria, tetanus, and pertussis immunization in children 6 weeks through 6 years of age" and "Diphtheria, tetanus, and pertussis immunization in children 7 through 18 years of age".)

Preventing HIV, hepatitis B virus (HBV), and hepatitis C virus (HCV) — In general, the risk of contracting HIV, hepatitis B, or hepatitis C from a human bite is negligible, but possible transmissions have been reported [14-19]. Transmission may be possible if the biter was bleeding from the mouth at the time of the bite and broke the skin of the bitten individual. In this situation, which is essentially a percutaneous blood exposure, either the biter or the bitten could theoretically become infected, and prophylaxis may be appropriate, as discussed separately. (See "Management of nonoccupational exposures to HIV and hepatitis B and C in adults".)

Uninfected bites — In a patient with no symptoms or signs of wound infection, management includes wound care and assessment for antibiotic, tetanus, and bloodborne pathogen prophylaxis.

Antibiotic prophylaxis

Indications for prophylaxis — Antibiotic prophylaxis is typically provided to patients whose wounds have an increased risk of infection, in agreement with expert guidelines [30].

We suggest post-exposure antibiotic prophylaxis in patients whose wounds break the skin and have any of the following features [30,31]:

●Involvement or proximity to deep structures (eg, tendon, bone, joint) or vascular graft

●Need for surgical repair or debridement

●Closure by primary intention (ie, the wound is sutured closed) or planned delayed primary closure, as discussed below (see 'Wound closure' below)

●Located on the hand, face, or genitals (including clenched-fist wounds)

●Located in areas of prior cellulitis or underlying venous and/or lymphatic compromise

●Immunocompromised patient (including diabetes)

●Patients at high risk for endocarditis (eg, prosthetic heart valve, certain congenital heart defects, heart transplant with valvular dysfunction) (see "Prevention of endocarditis: Antibiotic prophylaxis and other measures", section on 'Which patients?')

●Bites that have not received any wound care for more than eight hours

In the absence of the above factors, we do not favor use of post-exposure antibiotic prophylaxis. However, some experts favor routine use of antibiotic prophylaxis for human bites, even in the absence of the above factors. Most wounds that do not develop signs of infection by three days and have no retained foreign body will likely not become infected.

Evidence for post-exposure antibiotics is limited. In one randomized study of 48 patients with human bites to the hand, infection developed in 46 percent of patients who did not receive antibiotic prophylaxis; no infection developed among the patients who did receive antibiotic prophylaxis [24]. A trial of 125 patients with low-risk (penetrated only the epidermis and did not involve hands or feet) human bite wounds found that antibiotics, compared with placebo, did not reduce infection rates (infection developed in only one patient) [32].

Prophylactic antibiotic regimens — We prefer amoxicillin-clavulanate (875/125 mg every 12 hours in adults) for human bite prophylaxis. The first dose should be administered as soon as possible after the bite.

In a patient with a clenched-fist wound, some experts will administer one intravenous (IV) antibiotic dose followed by oral therapy [27]. This practice may provide more rapid attainment of therapeutic blood antibiotic concentrations, but evidence does not exist that it improves outcomes. (See 'Intravenous regimens' below.)

Antibiotic options for prophylaxis are the same as for treatment of infection, but the duration of prophylaxis is only three to five days (table 2) [30]. (See 'Oral regimens' below.)

Wound management

Indications for surgical consultation — Most human bites can be managed at the bedside. Surgical consultation is warranted in the following circumstances [33]:

●Clenched-fist wounds ("fight bites") with associated fracture, joint disruption, retained foreign body, or abnormal extensor tendon examination (see "Overview of hand infections", section on 'Human bites' and 'Physical examination' above)

●Complex facial lacerations (see "Assessment and management of facial lacerations")

●Deep wounds, especially if significant avulsion or amputation is present

●Wounds associated with neurovascular compromise

Clenched-fist injury wounds — A wound caused by a clenched-fist injury ("fight bite") should be irrigated, debrided, and explored, either at the bedside or by a surgeon in the operating room. In a patient with a normal extensor tendon examination and radiographs, it is reasonable to perform a bedside procedure and arrange surgical follow-up within 48 hours. Traditionally, it was recommended that these wounds be routinely evaluated by a surgeon and managed in the operating room, but insufficient evidence exists that every noninfected fight bite will have a better outcome with formal debridement in the operating room [4,27]. For example, a study of 115 adult patients with noninfected fight bites, normal extensor tendon examinations, and unremarkable radiographs found that operative debridement was associated with a higher complication rate compared with bedside irrigation (64 versus 7 percent) [27]. Patients who presented >24 hours after the injury had a higher complication rate and thus may be appropriate for surgical consultation.

A patient with a fight bite should receive prophylactic antibiotics, preferably intravenously for the first dose. (See 'Prophylactic antibiotic regimens' above.)

Wound closure — For most patients with human bite wounds, we suggest that the wounds be left open to heal by secondary intention rather than by primary closure, given the high risk of subsequent infection (see 'Assessing for infection' above). These wounds should undergo debridement of devitalized tissue, exploration for retained foreign material, copious irrigation, and have a dressing applied.

Primary closure is a reasonable alternative in a patient with a facial laceration, given the cosmetic importance of this area [3,28,33]. These wounds may be closed primarily if they are clinically uninfected and ≤24 hours old [28]. Wounds that are primarily closed should be cleaned following meticulous debridement and copious irrigation. We generally place nonabsorbing sutures in the skin (except for young children where removal would could be challenging and threaten the repair) and avoid placing subcutaneous sutures because foreign material increases the risk of infection [28]. Bite wounds should not be closed with tissue adhesive ("glue").

For a wound that may benefit from primary closure but is >24 hours old, the patient may be started on prophylactic antibiotics with a plan for delayed primary closure after three to four days. Unless the clinician has extensive experience with delayed primary closure, referral to a surgeon or other wound expert is advised since additional debridement (eg, of excessive accumulated granulation tissue) may be necessary at the time of closure. The waiting period during delayed primary closure permits the host defense system to decrease bacterial load and to ensure that no infection develops, which is a contraindication to closure. (See "Minor wound evaluation and preparation for closure", section on 'Delayed primary closure'.)

Patients who undergo primary closure warrant post-exposure antibiotic prophylaxis. (See 'Prophylactic antibiotic regimens' above.)

Infected bites — Patients with suspected wound infection are managed with antibiotic therapy, obtaining cultures, wound debridement, and tetanus and bloodborne pathogen prophylaxis, if indicated [28]. (See 'Tetanus and bloodborne pathogen prophylaxis' above.)

Antibiotic therapy

Choosing oral versus IV therapy — Oral antibiotic therapy is effective for most patients with infected wounds.

In the following circumstances, we administer IV antibiotics:

●Sepsis

●Rapidly progressive (eg, over hours) erythema

●Progression after 48 hours of appropriate oral antibiotics

●Deep-space infection (eg, necrotizing fasciitis, septic arthritis, clenched-fist injury)

●Proximity of the bite to an indwelling device (eg, prosthetic joint, vascular graft)

In a patient who has lymphangitis or an immunocompromising condition, we have a lower threshold for choosing IV therapy because these patients may be at increased risk for rapid or systemic progression of their infection.

In a patient who presents to the emergency department with an infected wound but does not meet the above criteria, some experts will administer one IV antibiotic dose followed by oral therapy. This practice may provide more rapid attainment of therapeutic blood antibiotic concentrations, but evidence does not exist that it improves outcomes.

Oral regimens — For oral treatment of infected human bites, we suggest choosing a regimen that covers streptococci, Staphylococcus aureus, E. corrodens, and anaerobic bacteria. We use one of the following antibiotic regimens:

●Preferred agent – We prefer amoxicillin-clavulanate (875/125 mg orally every 12 hours in adults; see table for pediatric dosing) (table 2).

●Alternative regimens – For a patient unable to take amoxicillin-clavulanate, we suggest combination therapy with one agent that covers aerobic bacteria and another that covers anaerobes.

For patients intolerant of beta-lactams, our favored regimen is dual therapy with trimethoprim-sulfamethoxazole (one double-strength tablet orally every 12 hours) plus metronidazole (500 mg orally three times a day); see table for pediatric dosing (table 2). Additional options are listed in the table (table 2), and selection may depend on the antibiotics' adverse effects.

We do not provide empiric coverage against methicillin-resistant S. aureus (MRSA) except in patients with abscess, MRSA risk factors (table 3 and table 4), or gram-positive cocci in clusters on Gram stain of the wound. Our preferred regimen for MRSA coverage is combination therapy with amoxicillin-clavulanate (875 mg orally every 12 hours) plus either trimethoprim-sulfamethoxazole (one double-strength tablet orally every 12 hours) or doxycycline (100 mg orally every 12 hours). Other antibiotics that cover MRSA are noted in the table (table 2). Issues related to risk factors and treatment of MRSA are discussed further separately. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Treatment of skin and soft tissue infections" and "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Epidemiology".)

Although clindamycin is an option for anaerobic coverage, we generally avoid it due to risk of Clostridium difficile infection. We also do not use it as monotherapy since it has no activity against E. corrodens, and streptococcal and staphylococcal resistance is possible, as discussed below and separately. (See 'Spectrum of antibiotic coverage' below and "Acute cellulitis and erysipelas in adults: Treatment", section on 'Alternatives for serious beta-lactam allergy'.)

Data from clinical studies are limited, and our antibiotic selections are primarily based on the typical microbiology of infected bite wounds. (See 'Spectrum of antibiotic coverage' below.)

Intravenous regimens — Our criteria for IV antibiotics are described above. (See 'Choosing oral versus IV therapy' above.)

Our preferred IV regimen for human bites is one of the following (table 5):

●Ampicillin-sulbactam (3 g IV every six hours in adults)

●Ceftriaxone (2 g IV once daily in adults) plus metronidazole (500 mg IV every eight hours in adults)

We add IV vancomycin to cover MRSA in patients who have severe illness, abscess, MRSA risk factors (table 3 and table 4), or gram-positive cocci in clusters on Gram stain of the wound.

For patients with necrotizing skin infection (eg, fasciitis), empiric antibiotic coverage is typically broader and targets toxin. Necrotizing skin infections are discussed in detail separately. (See "Necrotizing soft tissue infections", section on 'Treatment'.)

Once a patient has clinically responded to IV therapy, it is reasonable to de-escalate to oral therapy (table 2), unless the patient has another indication for prolonged IV therapy (eg, septic arthritis, prosthetic joint infection, osteomyelitis). Management of such infections are discussed in detail elsewhere. (See "Septic arthritis in adults", section on 'Treatment' and "Prosthetic joint infection: Treatment", section on 'Antibiotic therapy' and "Nonvertebral osteomyelitis in adults: Treatment", section on 'Antibiotic therapy'.)

Duration of treatment — The regimen should be tailored to culture and susceptibility data, once available. However, because anaerobic organisms can be difficult to grow in culture, we continue anaerobic coverage for the full course of therapy, even if anaerobic bacteria did not grow on culture.

The total duration of therapy is based on severity of infection and the patient's clinical response. In general, antibiotic therapy should be continued at least one to two days after symptoms and signs have resolved, which is typically less than seven days.

Most infections require no more than 14 days of therapy, but deep or complicated infections may require longer durations, particularly if a joint or bone is involved [30]. (See "Infectious tenosynovitis" and "Septic arthritis in adults" and "Nonvertebral osteomyelitis in adults: Treatment".)

Spectrum of antibiotic coverage — The spectrum of antibiotics for human bites are based on the pathogens most frequently isolated from infected wounds [26,34]. Scarce data are available to support specific antibiotic regimens for human bites; our suggestions are based on our clinical experience and generally agree with those of expert guidelines [30].

The best evidence is derived from a study of 50 patients with infected human bites that were cultured from 12 university-affiliated emergency departments in the United States in 2000 and 2001 [26]. The median number of isolates per wound culture was four (three aerobes and one anaerobe), and approximately half of the bites were classified as abscesses.

Antibiotic selection targets the most likely pathogens from human skin and oral flora:

●Human skin flora – The most common pathogen that originated from human skin in the aforementioned study was S. aureus, which was isolated from 15 of 50 (30 percent) of infected bites; the proportion of S. aureus isolates that were methicillin-resistant was not described [26]. Group A Streptococcus (ie, S. pyogenes) was uncommon, isolated from only 14 percent of bites.

●Human oral flora – Important human oral pathogens that caused infection included the following:

•Streptococcal spp other than Group A Streptococcus – Streptococcus anginosus group bacteria (ie, S. anginosus, S. intermedius, and S. constellatus) were isolated from 72 percent of human bites, the highest percentage of any microorganism [26]. These organisms are known to cause invasive infections and abscesses.

Streptococcal isolates are highly susceptible to beta-lactam antibiotics. However, studies of other antibiotics reveal variable results for the S. anginosus group. For example, resistance rates to tetracyclines (eg, tetracycline, doxycycline) ranging from 12 to 72 percent and to trimethoprim-sulfamethoxazole (TMP-SMX) of 2 to 45 percent have been reported [26,35-37]. Furthermore, isolates are often reported as susceptible to fluoroquinolones, but resistance can develop while on therapy [26,38,39]. More information on S. anginosus can be found separately. (See "Infections due to the Streptococcus anginosus (Streptococcus milleri) group".)

•Eikenella corrodens – This organism is isolated from 30 percent of human bites. E. corrodens are fastidious organisms that may be misidentified by the microbiology laboratory. The organism is part of the HACEK group of endocarditis-causing organisms, as discussed separately; however, most Eikenella endocarditis cases are associated with IV drug abuse as opposed to human bites. (See "Antimicrobial therapy of left-sided native valve endocarditis", section on 'HACEK organisms'.)

In vitro studies of clinical isolates show that E. corrodens is typically resistant to penicillinase-resistant penicillins (eg, dicloxacillin), first- and second-generation cephalosporins (eg, cephalexin), clindamycin, metronidazole, and aminoglycosides [26,40-44]. Such studies consistently reveal susceptibility to penicillin, amoxicillin, tetracyclines, fluoroquinolones, TMP-SMX, ceftriaxone, and carbapenems [26,40-43,45-47].

•Anaerobes – Anaerobes are present in at least half of infected wounds [26]. Specific isolates include Prevotella species, fusobacteria, Veillonella species, and peptostreptococci. Unlike dog and cat bites, Bacteroides spp are uncommon in human bites, occurring in <5 percent [48,49].

Debridement and surgical consultation — Debridement of infected tissue is an important component of management for infection associated with a human bite. If previously repaired, suture material should be removed. Associated abscess(es) should be drained. (See "Basic principles of wound management", section on 'Wound debridement' and "Techniques for skin abscess drainage".)

Debridement can often be performed at the bedside. However, we obtain urgent surgical consultation for bite-associated infection for any of the following [33]:

●Concern for necrotizing soft tissue infection (eg, rapidly progressive infection, crepitus)

●Clenched-fist injuries (these often require operative joint exploration) (see "Overview of hand infections", section on 'Human bites')

●Deep-space infection (eg, deep abscess, septic arthritis, osteomyelitis, pyomyositis)

●Hand flexor tenosynovitis

●Purulent facial infection with concern for cosmetic deformity

●Persistent signs and symptoms of infection despite appropriate antibiotic therapy

●Infection associated with neurovascular compromise

●Retained foreign body that cannot be removed at the bedside

At the time of debridement or surgery, deep tissue samples should be obtained for culture, as described above. (See 'Cultures (wound, blood)' above.)

In general, infected bite wounds should be left open following debridement. Delayed primary closure may be appropriate for facial wounds, large lacerations, and disfiguring wounds, as described above. (See 'Wound closure' above.)

FOLLOW-UP CARE — All patients with human bites require close follow-up. We examine all wounds two to three days after initial presentation, regardless of infection status or type of closure. A clenched-fist injury wound should be evaluated by a hand surgeon at least within two days. We instruct the patient (or caregivers) to be evaluated sooner if they are concerned that signs or symptoms of infection are developing or worsening (if already present). Afterwards, the frequency of follow-up is individualized based on extent of healing and need for suture removal (if indicated). Some experts will evaluate infected wounds daily until significant clinical improvement has been documented, but this may be onerous for the patient and unnecessary in a patient (or caregivers) who can reliably monitor the wound.

Signs of developing or worsening infection on follow-up examination should prompt further wound evaluation (with radiographic imaging and/or surgical consultation, if indicated), suture removal (if present), review of antibiotic regimen and culture results, and/or a switch to IV therapy.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Skin and soft tissue infections" and "Society guideline links: Human bites".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Beyond the Basics topic (see "Patient education: Animal and human bites (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Types of human bites – Occlusal bites are frank bites by human teeth; they appear as semicircular or oval areas of erythema or bruising and the skin may or may not be intact. A bite mark on a child with maxillary intercanine distance (distance between left and right canine from the outer edge of the tooth) >2.5 cm suggests the bite came from an adult and should raise concern for child abuse (picture 2). (See 'Types of bites' above.)

Clenched-fist injuries ("fight bites") occur when the clenched fist of one person strikes the teeth of another (figure 1); lacerations are typically over the third and fourth metacarpophalangeal or proximal interphalangeal joints of the dominant hand. These are highly prone to infection. (See 'Clenched-fist injuries' above and 'Assessing for infection' above.)

●Initial evaluation

•Wound preparation – Initial wound care helps to prevent infection and facilitates examination; it includes applying direct pressure to control any bleeding, cleansing and irrigating the wound, and removing any visible debris. (See 'Wound preparation' above.)

•Physical examination – Examine the wound for proximity to important structures (eg, bone, joints), depth, neurovascular compromise, foreign material, cosmetic implications, and signs of infection (including flexor tenosynovitis). Wounds over or near the metacarpophalangeal joints should be explored in the relaxed, fingers-extended, and the clenched-fist positions to ensure the wound does not involve tendons or communicate with a fracture or joint (picture 1). A clenched-fist injury requires evaluation of finger extensor mechanism function. (See 'Physical examination' above and 'Assessing for infection' above.)

•Role of imaging and cultures – We obtain plain radiographs in patients with clenched-fist injuries or if there is concern for fracture, joint disruption, or retained foreign body. Wound cultures should be obtained from infected wounds. (See 'Ancillary tests' above.)

●Tetanus and bloodborne pathogen prevention – For a patient fully vaccinated against tetanus, we administer a tetanus toxoid-containing vaccine only if their last dose was given ≥5 years ago (or if the date of their most recent vaccine is uncertain). For unvaccinated or partially vaccinated patients, we administer a tetanus toxoid-containing vaccine and tetanus immune globulin (table 1). (See 'Tetanus prophylaxis' above.)

The risk of transmission of HIV, hepatitis B, and hepatitis C from human bites is negligible but possible, especially if the biter was bleeding from the mouth at the time of the bite and broke the skin of the bitten individual. (See 'Preventing HIV, hepatitis B virus (HBV), and hepatitis C virus (HCV)' above and "Management of nonoccupational exposures to HIV and hepatitis B and C in adults".)

●Management of uninfected bites

•Antibiotic prophylaxis – In selected patients at risk of infection, we suggest post-exposure antibiotic prophylaxis (Grade 2C). We use amoxicillin-clavulanate (875/125 mg orally every 12 hours in adults for three to five days; see table for pediatric dosing) (table 2). Such patients include those whose wounds have any of the following features (see 'Antibiotic prophylaxis' above):

-Involvement or proximity to deep structures (eg, tendon, bone, joint) or vascular graft

-Need for surgical repair or debridement

-Closure by primary intention (ie, the wound is sutured closed) or planned delayed primary closure

-Located on the hand, face, or genitals (including clenched-fist wounds)

-Near a bone, joint (including prosthetic joints), or vascular graft

-Located in areas of prior cellulitis or underlying venous and/or lymphatic compromise

-Immunocompromised patient (including diabetes)

-Patients at high risk for endocarditis (see "Prevention of endocarditis: Antibiotic prophylaxis and other measures", section on 'Which patients?')

-Bites that have not received any wound care for more than eight hours

A patient with a clenched-fist wound should preferably receive the first dose intravenously.

•Wound care – Most human bites can be managed at the bedside. Surgical consultation is warranted for clenched-fist wounds with associated fracture, joint disruption, retained foreign body, or abnormal extensor tendon examination; complex facial lacerations; deep wounds (especially if significant avulsion or amputation is present); and wounds with neurovascular compromise. (See 'Indications for surgical consultation' above.)

For a clenched-fist wound with a normal extensor tendon examination and radiographs, it is reasonable to irrigate, debride, and explore at the bedside and arrange surgical follow-up within 48 hours. (See 'Clenched-fist injury wounds' above.)

We suggest that most human bite wounds be left open to heal by secondary intention (rather than closed primarily), given the high risk for the development of infection (Grade 2C). These wounds should undergo debridement of devitalized tissue, exploration for retained foreign material, copious irrigation, and have a dressing applied. Primary closure is a reasonable alternative in a patient with an uninfected facial laceration given the cosmetic importance of this area. (See 'Wound closure' above.)

●Management of infected bites – Most patients with infected bites can be managed as outpatients with oral antibiotics.

We suggest treatment with amoxicillin-clavulanate (875/125 mg orally every 12 hours in adults; see table for pediatric dosing) (Grade 2C). Our preferred intravenous (IV) option is ampicillin-sulbactam (3 g IV every six hours). Other options are listed in the tables (table 2 and table 5). (See 'Antibiotic therapy' above.)

Our preferred regimens cover the most frequently isolated organisms from human bites and are well tolerated in most patients. Most patients do not require empiric coverage for methicillin-resistant Staphylococcus aureus (MRSA). (See 'Spectrum of antibiotic coverage' above and 'Oral regimens' above.)

Selected patients (eg, infected clenched-fist injuries) may require IV and/or broader spectrum coverage, as described above. (See 'Choosing oral versus IV therapy' above.)

Debridement of devitalized tissue, removal of foreign material, and drainage of abscess should be performed. Wounds should be left open to heal by secondary intention. Urgent surgical consultation is appropriate for infected clenched-fist injuries (these often require operative joint exploration), hand flexor tenosynovitis, deep space infections, purulent facial infections, and others. (See 'Debridement and surgical consultation' above.)