Human Bite-induced Cellulitis Due to Streptococcus pyogenes

The rate of infection after a human bite is 10%-30%. Streptococcus spp. are the most common pathogens that may cause serious infections, such as necrotizing fasciitis. The authors describe a 5-year-old girl admitted to the emergency room with cellulitis due to S. pyogenes after human bites. She presented with fever and pain in her left arm, and her medical history revealed a human bite by her cousin on the arm 3 days prior. The wound culture yielded S. pyogenes. She was successfully treated with intravenous ampicillin-sulbactam regimen. S. pyogenes may cause serious wound infections following human bites. In such cases, the patient should be closely followed. Chemoprophylaxis should be initiated in an appropriate clinical setting to prevent secondary bacterial infections. This case was first reported as cellulitis due to S. pyogenes after a human bite.

One percent of all pediatric visits to emergency departments are due to animal or human bites.¹ In the United States, the estimated annual incidence of bites ranges from 1 million to 2 million dog bites, 400,000 cat bites, and 250,000 human bites.¹ Human bite wounds often result from incidental or deliberate injury and peak in the spring and early summer. Human bites are more prone to infection than animal bites, with the rate of infection following a human bite being 10%-30%.² The risk factors of infection include the patient’s age, type of the wound, location of the wound, and time from the bite to initiation of treatment. Hand injuries are more likely to become infected than bites to the arm, leg or face. In addition, puncture wounds more often become infected than lacerations, superficial wounds, and skin soft tissue defects. Infections occur more easily in cases of delayed treatment or surgical repair of the wound.² 

The sources of bite wound infections are polymicrobial flora of the oral flora of the biter, skin flora of victim, and environmental saprophytic microorganisms.³ These pathogens are both aerobic and anaerobic bacteria including Streptococci, Staphylococcus aureus, Eikenella corrodens, Fusobacterium, Prevotella, Peptostreptococcus, Veillonella and Porphyromonas spp.³ The most frequent isolate is the α-hemolytic streptococci, particularly Streptococcus anginosus.³ Infected bite wound cultures often yield bacterial pathogens; 85% of cases yield bacterial pathogens even before the onset of clinical infection.⁴ Viral pathogens including hepatitis viruses, human immunodeficiency virus, herpes simplex virus, and cytomegalovirus virus are transmissible by human bites.^5-7

Clinical manifestations of human bite infections include tenderness, erythema, swelling, purulent drainage, lymphangitis, and fever. Human bite injuries are also at risk for deep soft tissue infection, tendonitis, septic arthritis, and osteomyelitis. Streptococcus spp., the most common pathogen, may cause cellulitis, erysipelas, or more serious infections such as necrotizing fasciitis. The authors present the case of a 5-year-old girl who developed cellulitis due to S. pyogenes after a human bite.

A 5-year-old girl was admitted to the emergency room with fever and pain in her left arm. Her medical history revealed a human bite by her cousin in her arm 3 days prior to presentation, and that prophylactic antibiotherapy was not initiated. At the time of presentation, she had an axillary temperature of 38.5ºC (101.3ºF). Her left arm was erythematous and edematous. In the erythematous site, there was a purulent drainage and skin and subcutaneous tissue defect near her elbow (Figure 1). Laboratory evaluation of the patient was as follows: hemoglobin, 10.3 g/dL; white blood cell count, 11.3x10³/µL; and C-reactive protein, 3.44 g/dL (0-5). Liver transaminases were in normal range. Renal function values were in normal range. A blood culture was taken from the peripheric venosus vessel and incubated with the BacT/ALERT 3D device (bioMérieux, Inc, Durham, NC) for both aerobic and anaerobic cultures. An aerobic culture was taken from the pus and an intravenous ampicillin-sulbactam regimen was empirically initiated. The patient’s previous tetanus immunization had already been completed; therefore, no tetanus prophylaxis was given. The patient and her cousin were investigated for viral hepatitis and human immunodeficiency virus (HIV), and the serology test results of these pathogens were all negative. Serum hepatitis B surface antibody (anti-Hbs) concentration was 9.22 mIU/mL in the patient, and serum anti-Hbs concentration was 8.00 mIU/mL in the biter. The authors recommended a second series of hepatitis B immunization to both children because of failure to develop a serum anti-Hbs response (10 mIU/ml or greater). The wound culture yielded S. pyogenes. On day 7 of admission, erythema and edema resolved and the patient was discharged with an oral amoxicillin-clavulanate regimen for 7 days. 

Written informed consent was obtained from the patient’s parents for publication of this case report and any accompanying images.

Human bites are more prone to wound infections than animal bites, with the rate of infection after a human bite being 10%-30%.¹ The pathogens of bite wounds are usually polymicrobial flora of the oral flora of the biter, skin flora of the victim, and the environment. Streptococcus spp. and Staphylococcus spp. are the most common organism; however, both aerobic and anaerobic bacteria, including Eikenella corrodens, Fusobacterium, Peptostreptococcus, Prevotella, Veillonella, and Porphyromonas spp. also are isolated in wound cultures.³ Clinical manifestations of human bite infections include tenderness, erythema, swelling, purulent drainage, lymphangitis, and fever. Human bite injuries are also at risk for cellulitis, necrotizing fasciitis, deep soft tissue infection, tendonitis, septic arthritis, and osteomyelitis. Cellulitis is characterized by hyperemia, edema dissemination, and acute inflammation within the dermis and cutaneous tissue, but without cellular necrosis. The most common cause of cellulitis is S. pyogenes after human or animal bites, and α-hemolytic streptococcus, S. aureus, E. corredens may induce cellulitis. 

In the treatment of wound infections following human bites, no comparative trials investigating antibiotic therapies are available. In the treatment of human bite infections, antibiotic therapy should be selected based on the counteractivity to oral and skin flora including Streptococcus spp., Staphylococcus spp. and others, both aerobic and anaerobic bacteria, such as Eikenella corrodens, Haemophilus Fusobacterium, Peptostreptococcus, Prevotella, Veillonella, and Porphyromonas spp. The bacteriological examination of an infected human bite wound demonstrated the wound culture may yield polymicrobial isolates and the median number of isolates per wound culture is 4. In such cases, both aerobes and anaerobes are isolated from 54% of wounds and individually aerobes and anaerobes are isolated from 44% and 2% of wounds, respectively.³ Anaerobic wound infections may result in more serious infections requiring amputation or presenting with abscesses than aerobic wound infections. Most pathogens of wound infection produce beta-lactamases except S. pyogenes, which is still sensitive to penicillin G. Eikenella corrodens is resistant to β-lactamase-stable penicillins and first-generation cephalosporins. The combination amoxicillin-clavulanate has an extended spectrum of activity against both gram-positive and gram-negative bacteria and exhibits good tissue penetration. The amoxicillin-clavulanate combination can be used in polymicrobial infection such as human bite or animal bite-induced wound infections.⁸ In addition, as an alternative therapy, the second-generation or third-generation cephalosporins with anaerobic coverage such as metronidazole or clindamycin can be used.⁸ In the described case, an ampicillin-sulbactam regimen was initiated empirically based on the results of wound culture. The clinical findings of cellulitis resolved in a few days, the wound culture yielded S. pyogenes, and antibiotic treatment was continued with amoxicillin-clavulanate for 7 days. 

A review of the literature revealed 4 cases in which skin and soft tissue infections due to S. pyogenes developed after a human bite. All of them were diagnosed as necrotizing fasciitis in the clinical presentation. These necrotizing fasciitis due to S. pyogenes were treated with surgical debridement and antibiotic therapy. Three of cases were successfully treated; however, 1 patient died due to multiorgan failure.^9-11 The case described in this paper was first reported as cellulitis due to S. pyogenes after a human bite.

There is no consensus on antibiotic prophylaxis after human bite infections. Some patients are admitted to the emergency room immediately after a bite and, in such cases, there may not be an evidence of infection. Guidelines recommend preemptive antibiotic therapy in immunocompromised hosts, deep puncture wounds, moderate and severe wounds of the hand and face, wounds near the periosteum and joint capsule, and wounds requiring surgical repair.^4,8 A Cochrane collaboration review showed the use of prophylactic antibiotics following a human bite may reduce the infection rates, and that appropriate oral antibiotics should be given for 3-5 days.¹² 

Viral hepatitis, herpes viruses, and HIV can be transmitted by a human bite, whereas exposure to human saliva is not a risk factor for viral transmission. If there is blood in the biter’s mouth, it may become a risk for transmission. In the case of a known biter, he or she should be evaluated for HIV and hepatitis B surface and enveloped antigens. In the literature, HIV transmission by a human bite has been reported in a few case reports.⁵ Postexposure prophylaxis for HIV is indicated routinely after human bites if the biter is found to be HIV infected.¹³ Also, human bites are risk factors for hepatitis B virus transmission;⁷ the vaccine should be given immediately to unvaccinated individuals, individuals with antibody-negative test results, and/or if the biter tested positive for HbsAg hepatitis B immunoglobulin and hepatitis B. Postexposure prophylaxis should be planned according to the infectious status of the biter and the immune status of the patient.¹⁴

In conclusion, S. pyogenes may cause serious wound infections following human bites. In such cases, the patient should be closely followed. Chemoprophylaxis should be initiated in an appropriate clinical setting to prevent secondary bacterial infections. Depending on the polymicrobial nature of these infections, antimicrobial therapy should be selected. 

Affiliation: Division of Pediatric Infectious Diseases, Department of Pediatrics, Marmara University School of Medicine, Istanbul, Turkey

Correspondence:
Ahmet Soysal
asoysal@marmara.edu.tr

Disclosure: The authors disclose no financial or other conflicts of interest.