Cellulitis and Diabetic Foot Infections

Chapter 11 Cellulitis and Diabetic Foot Infections



Key Points



Cellulitis


1 Most cases of cellulitis are caused by gram-positive cocci (Streptococcus pyogenes and Staphylococcus aureus).

2 Patients with unusual exposures (see Table 11-1), recent antibiotic use, or vascular and lymphatic compromise may be at risk for infection by other organisms.

3 Blood and wound cultures should be reserved for patients with exposures listed in Table 11-1; lymphatic, vascular, or immune compromise; increased likelihood of resistant organisms; or lack of response to empiric therapy.

4 Patients with evidence of systemic toxicity or rapid progression of infection should receive inpatient parenteral therapy. Milder infections can be treated successfully in the outpatient setting.

5 Empiric therapy with nafcillin, dicloxacillin, or cefazolin should be initiated. Appropriate coverage for unusual exposures (see Table 11-1) should be given as well.

Diabetic Foot Infection


1 Neuropathy, vascular insufficiency, and hyperglycemia contribute to the development of foot ulcers, which subsequently become colonized and infected.

2 Acute infections are usually caused by gram-positive cocci.

3 Patients with chronic ulcers, recent hospitalizations, or recent antibiotic use may have a polymicrobial infection with gram-positive cocci, gram-negative bacteria, and resistant organisms.

4 Assessment of the patient with a diabetic foot infection should include the clinical status, any predisposing factors such as anatomic abnormalities or vascular insufficiency, the size and extent of the ulcer, and local complications such as abscess formation or osteomyelitis.

5 Biopsies of the cleaned and débrided wound site should be obtained.

6 Choice of empiric antibiotics depends on the infection severity and risk factors for resistant organisms.

7 Osteomyelitis should be suspected in patients with visible bone, bone that can be palpated using a metal probe, or ulcers that do not heal after 6 weeks of appropriate therapy.

Table 11-1 Probable Etiology of Soft Tissue Infections Associated with Some Specific Risk Factors or Settings







































































Risk Factor Potential Infectious Organism Treatment
Cat bite Pasteurella multocida Amoxicillin-clavulanate, ampicillin-sulbactam, cefoxitin
P. multocida is resistant to dicloxacillin and nafcillin
Dog bite P. multocida, Capnocytophaga canimorsus, Staphylococcus intermedius Amoxicillin-clavulanate, ampicillin-sulbactam, cefoxitin
P. multocida is resistant to dicloxacillin and nafcillin
Human bite Eikenella corrodens, Fusobacterium, Porphyromonas, Prevotella, S. pyogenes Amoxicillin- clavulanate, ampicillin-sulbactam, cefoxitin
Hot tub exposure Pseudomonas aeruginosa Aminoglycosides, third-generation cephalosporins, ticarcillin, mezlocillin, piperacillin, fluoroquinolones (in adults)
Diabetes mellitus or peripheral vascular disease Group B streptococci Penicillin or erythromycin
Periorbital cellulitis in children Haemophilus influenzae Third-generation cephalosporin
Saphenous venectomy site Groups C and G streptococci Penicillin or erythromycin
Fresh water laceration Aeromonas hydrophilia Trimethoprim- sulfamethoxazole, fluoroquinolones, aminoglycosides, chloramphenicol, third-generation cephalosporins; resistant to ampicillin
Sea water exposure, raw oysters, and cirrhosis Vibrio vulnificus Tetracyclines
Stasis dermatitis or lymphedema Groups A, C, G streptococci Penicillin or erythromycin
Cat scratch, or bacillary angiomatosis in an HIV patient Bartonella henselae, B. quintana Erythromycin
Fish mongering, bone rendering Erysipelothrix rhusiopathiae Erythromycin, clindamycin, tetracycline, cephalosporins; resistant to sulfonamides, chloramphenicol
Fish tank exposure Mycobacterium marinum Rifampin and ethambutol
Contact with others with soft tissue infections Methicillin-resistant S. aureus Vancomycin
Compromised host with ecthyma gangrenosum P. aeruginosa Aminoglycosides, third-generation cephalosporins, ticarcillin, mezlocillin, piperacillin, fluoroquinolones (in adults)

Stevens DL. Cellulitis, pyoderma, abscesses and other skin and subcutaneous infections. In: Cohen J, Powderly WG, Berkley SF, et al. Infectious Diseases, 2nd ed. Philadelphia: Mosby; 2004. p. 133.



Definition and Epidemiology


Cellulitis is a skin and subcutaneous tissue infection that can affect any part of the body. Cellulitis is most commonly caused by Staphylococcus aureus and Streptococcus pyogenes. However, other infectious agents may predominate in different clinical situations (Table 11-1). Although cellulitis is quite common, accurate incidence information is not available. Some estimates suggest that cellulitis accounts for approximately 2% of outpatient office visits, or up to 158 visits per 10,000 person-years.


The term diabetic foot infection refers to a spectrum of foot infections in patients with diabetes mellitus that ranges from a limited cutaneous infection to osteomyelitis, but most commonly refers to an infection of a foot ulcer. These foot infections are a major source of morbidity in patients with diabetes mellitus; more than one half of diabetics hospitalized with a foot infection subsequently require amputation.



Pathogenesis



Risk Factors for Cellulitis



General


Risk factors for cellulitis include obesity, vascular or lymphatic compromise (e.g., venous insufficiency, saphenous venectomy, or lymph node dissection after surgery for breast cancer), lower extremity edema, diabetes mellitus, and skin trauma (e.g., pressure ulcers, trauma or tinea pedis).


Patients without vascular or immune defects will likely be infected by S. aureus or group A streptococci. Pseudomonas, enterococci, or other bacteria may cause cellulitis in patients with an immune or vascular defect, or loss of significant skin integrity (e.g., burns).



Breast Cancer


Women who have undergone surgery for breast cancer with axillary lymph node dissection are at risk for recurrent cellulitis in the ipsilateral breast and upper extremity. Disruption of normal lymphatic drainage is thought to play a role in pathogenesis.



Saphenous Venectomy


Patients with saphenous venectomy are at increased risk for recurrent cellulitis because of vascular and perhaps lymphatic impairment. Tinea pedis appears to be a significant risk factor in this patient population, serving as a site of entry for microorganisms.



Pathogenesis of Cellulitis


Bacteria penetrate the cutaneous barrier through breaks in the skin or via hair follicles. Microbial cell wall components (e.g., endotoxins, peptidoglycans) stimulate production of chemotactic factors, which attract neutrophils to the region. Continued production of pro-inflammatory cytokines causes fever and local changes of erythema, edema, warmth, and pain.


Patients with decreased tissue perfusion as a result of vascular disease (e.g., atherosclerosis, diabetes) may have an increased susceptibility to cellulitis and are predisposed to deeper soft tissue infections.



Risk Factors for Diabetic Foot Infections


Diabetic foot infections occur as a result of multiple risk factors that result in an initial break in the protective skin barrier and an increased susceptibility to infection:


• Peripheral neuropathy
image Motor neuropathy leads to changes in foot anatomy (neuro-osteoarthropathic deformities), resulting in deformities such as high arch and abnormal toe positioning that increase the risk of ulcer formation.

image Sensory neuropathy decreases pain sensation so that diabetic patients are not aware of ulcer formation or injury.

image Autonomic neuropathy causes dry skin that is more prone to trauma.

• Hyperglycemia negatively impacts wound healing and white blood cell (particularly polymorphonuclear cell) function.

• Peripheral vascular disease hinders wound healing, causes tissue ischemia, and impairs neutrophil chemotaxis.


Pathogenesis and Microbiology of Diabetic Foot Infections


The initial break in overlying skin is usually caused by trauma or pressure ulceration. The area becomes colonized with bacteria, and becomes infected over a period of hours to days.


• Acute infection in an antibiotic-naïve patient who has not been recently hospitalized is usually caused by gram-positive cocci (S. aureus and beta-hemolytic streptococci).

• Chronic infections are polymicrobial. Gram-negative rods (e.g., Pseudomonas, Escherichia coli), anaerobes, and enterococci may be present in addition to S. aureus and streptococci.

• Recent hospitalization or use of antibiotics favors growth of fungi and antibiotic-resistant organisms such as methicillin-resistant S. aureus and vancomycin-resistant enterococci.


Clinical Features and Diagnosis



Cellulitis



History


Patients may or may not report a history of trauma to the region. Exposure history may provide clues to specific infections, as detailed in Table 11-1. Risk factors such as a history of tinea pedis, diabetes mellitus, surgery for breast cancer with lymph node dissection, saphenous venectomy, or peripheral vascular disease should be determined.


Patients in close contact with other persons who have soft-tissue infections may be at higher risk for methicillin-resistant S. aureus (MRSA) infections.

Related posts:

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  2. Diabetic Ketoacidosis
  3. Anemia
  4. Acute Lower Gastrointestinal Bleed

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Mar 25, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Cellulitis and Diabetic Foot Infections

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