M. H. Lupin, BSc, MD, FRCPC

Department of Dermatology, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada


Whereas the internal tissues of humans are normally free of microorganisms (save for some viruses), the “external” tissues, including the skin and gut, have a complex flora. The number of microorganisms far exceed the number of human cells, with more than 200 species of bacteria, along with eukaryotic fungi, and protists. Herpes viruses stay with us for life and reside in our nerves; the human papillomavirus also stays with us for life and resides in our skin cells. Generally, the relationship is commensal or mutualistic; however, when there is a breakdown in the integrity of the skin, or our immune defense is compromised, infections can result.



Discrete Lesions

Diffuse Lesions

Superficial InfectionsImpetigo
Deep InfectionsEcthyma
Necrotizing Fasciitis (NF)*
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Most Common Pathogens





Staphylococcus aureus
Streptococcus pyogenes


Impetigo and Ecthyma

  • Typically honey-colored crust with erythematous vesicles, papules, pustules, or erosions; common area around nose and face.
  • Children with atopic dermatitis are more susceptible.
  • N onbullous – usually S. pyogenes +/- S. aureus. S. aureus is more common in the northern climates; Bullous – usually S. aureus.
  • Ecthyma is a deeper version of impetigo, more commonly seen in patients with malnutrition and/or poor hygiene – vesicles and bullae progress to punched-out, deep ulcers with adherent, dehydrated, serosanguinous crust; legs are the most common site and healing leaves scars


  • Nonbullous: fusidic acid (Fucidin® cream) t.i.d. or mupirocin (Bactroban® Cream) t.i.d.
  • Bullous: cloxacillin (Cloxapen®) 500mg, po, q6h or cephalexin (Keflex®) 500mg, po, q6h

Folliculitis, Furunculosis and Carbunculosis (Folliculitis Group)

  • A spectrum of infections involving the hair follicles
  • Characterized by erythematous follicular-based papules and pustules. Hairs may be visible at the center of them.
  • Often asymptomatic or minimally pruritic
  • Hot tub folliculitis less common and due to Pseudomonas aeruginosa – usually clears spontaneously and is commonly distributed over the trunk, buttocks, and thighs.
  • Furunculosis is a deeper infection of the hair follicle presenting with tender, erythematous nodules and suppurative drainage.
  • Carbuncles are a coalescence of furuncles presenting as larger, tender, fluctuant, draining, inflammatory nodules.


  • Fusidic acid t.i.d. is indicated for bacterial folliculitis and bacterial paronychia.
  • Cloxacillin 500mg, po, q6h or cephalexin 500mg, po, q6h


  • Fluctuant cystic nodule, may have a pointing pustule
  • Usually tender and occasionally painful or sore
  • S. aureus is the usual culprit
  • Incision and drainage (I & D) is most important as well as taking cultures
  • If there is a cellulitic component >5cm; if abscess cannot easily be drained; if location is on face; or if there are systemic symptoms (fever, chills); add a systemic antibiotic.


  • Fusidic acid t.i.d. is indicated and can be used alone or most commonly in combination especially in smaller lesions.
  • Cloxacillin 500mg, po, q6h or cephalexin 500mg, po, q6h

Erysipelas and Cellulitis

  • Erysipelas is a superficial infection with a predilection for young children and the elderly.
  • Venous insufficiency, alcoholism, diabetes mellitus, and trauma are predisposing factors.
  • Tender, well-defined erythematous and indurated plaques, most commonly on the face or legs, are characteristic of erysipelas.
  • Cellulitis is a deeper process extending to the subcutis.


  • Face: vancomycin (Vancocin®) 1g, IV, q12h
  • Extremities – mild:
    • Cloxacillin 500mg, po, q6h OR cephalexin 500mg, po, q6h
  • Extremities – severe:
    • Penicillin G 1-2mU, IV, q6h OR cloxacillin 2g, IV, q4h
    • Trimethoprim/sulfamethoxazole (Septra® DS) b.i.d. + rifampin 300mg, po, b.i.d. (for diabetics) OR Clarithromycin (Biaxin XL®)
    • 500mg, po, q.d., OR azithromycin (Zithromax®) 500mg, q.d. x 3 days


  • Antibacterial washes such as triclosan (Trisan®, Tersaseptic®) and chlorhexidine gluconate (Hibitane®) may be considered 2-3 times/day.
  • Warm compresses for 15-20 minutes 3-4 times/day.
  • Important to consider I&D for larger furuncles, and carbuncles, and as a primary treatment of abscesses.

Treatment Algorithm

Treatment Algorithm


Bacterial Resistance

  • Due to increased bacterial resistance to drugs in general, always obtain cultures if possible and test for drug sensitivity.
  • A marked increase in methicillin resistant S. aureus (MRSA) has been noted in Canada and the US with as much as a 5-fold increase in prevalence in 2005 compared with 2003.
  • In British Columbia in 2006, a dramatic increase in community-acquired MRSA has been noted. Clinically these infections look more aggressive.
  • A presentation at a recent Canadian Association for Clinical Microbiology and Infectious Disease conference reported that monitoring shows that sensitivity of MRSA to topical fusidic acid has remained high (96%).
  • The Centre for Disease Control has recommended that MRSA be a reportable disease.
  • Community-acquired MRSA (CA-MRSA) is usually resistant in vitro to ß-lactams (penicillin and cephalosporins) as well as macrolides/azalides (erythromycin, clarithromycin, azithromycin).
  • CA-MRSA tends to be sensitive to TMP/SMX (trimethoprim/ sulfamethoxazole), tetracyclines (e.g., doxycycline [Doryx®], minocycline [Minocin®] and clindamycin [Cleocin®]) although resistance can occur.
  • Hospital acquired MRSA (HA-MRSA) is usually resistant in vitro to multiple classes of antibiotics.

Measures to Help Minimize Bacterial Resistance

  • Wash hands for 10-15 seconds with a good antibacterial wash.
  • Povidine-iodine is good as a disinfectant.
  • Counsel patients on the need to take a full course of prescribed therapy.
  • Disinfect office furniture and office instruments, including stethoscopes, regularly.
  • Culture any skin infection, if possible.
  • I & D alone with warm compresses may be sufficient for uncomplicated abscesses (vide supra).
  • Avoid routine use of antibacterial soaps, toothpaste etc.
  • Canadian Committee on Antibiotic Resistance (www.ccar-ccra.com) is a good reference for up-to-date information on resistance patterns.
  • Some antibiotics have ongoing Canadian sensitivity programs to monitor and confirm continued effectiveness against relevant bacterial pathogens.


  • Nasal carriage of S. aureus is approximately 20%-30%, so it is important to treat the nose if there is frequent recurrence of infection or an outbreak among close family members. Mupirocin cream q.h.s. for 6 weeks is helpful. Rifampin can be added if needed. Routine treatment of the nose is not recommended.
  • Folliculitis has a differential diagnosis of acne, irritant folliculitis, pityrosporum folliculitis, and candidal folliculitis.
  • Acute paronychia is an inflammation around the nails and is commonly due to S. aureus, and occasionally Candida albicans; consider using a topical corticosteroid along with antibiotic therapy.
  • Tinea corporis, which is inappropriately treated with corticosteroid creams, can present similarly to a folliculitis due to dermatophyte infection; take a skin scraping and pluck hair for fungal stains and culture.
  • A full medical history, including family history of allergies, is imperative before prescribing any antibiotic therapy.
  • For leg cellulitis, rule out and treat tinea pedis as a common portal of entry.


Recognition and appropriate treatment of these common bacterial skin infections, while at times challenging, can be very rewarding for both the physician and the patient. Selecting the right therapy from the beginning should help minimize complications, reduce the number of hospitalizations, and may also help reduce the climbing incidence of bacterial resistance.