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What is Pyoderma?
Pyodermas are bacterial skin infections caused by pyogenic bacteria, most commonly Gram-positive organisms such as staphylococci and streptococci, capable of triggering inflammatory reactions characterized by pus formation.
These infections are classified according to the depth of skin involvement and range considerably in severity:
Epidermal pyodermas (affecting the outermost skin layer):
- Impetigo
- Whitlow / Paronychia
- Folliculitis
Dermal pyodermas (affecting the dermis, immediately beneath the epidermis):
- Erysipelas
- Suppurative hidradenitis
Deep pyodermas (affecting the hypodermis and deeper structures):
- Phlegmon (cellulitis)
- Necrotizing fasciitis
This article focuses on the three most common superficial pyodermas: impetigo, folliculitis, and whitlow. For erysipelas, suppurative hidradenitis, and deep pyodermas, please refer to the dedicated articles on each condition.
Causes and Risk Factors
Pyodermas are caused by Gram-positive cocci (spherical-shaped bacteria), primarily:
- Staphylococcus aureus
- Streptococcus pyogenes (Group A Streptococcus)
- Haemophilus influenzae
Staphylococcus aureus deserves particular attention: it is a normal component of human intestinal flora and can be isolated from the nasopharynx and skin, especially the perineal region and nasal passages, in 30–50% of healthy individuals. While it is typically harmless in this carrier state, it becomes pathogenic when skin barrier integrity is compromised.
Predisposing Factors
The following conditions and circumstances are known to facilitate the development of pyodermic infections:
- Surgical procedures (disruption of skin integrity)
- Minor trauma, including waxing, shaving, and other hair-removal techniques (particularly relevant for folliculitis)
- Contact with soil or beach sand
- Hot and humid climate (promotes bacterial proliferation)
- Pre-existing skin lesions, especially weeping or oozing wounds
- Eczema associated with atopic dermatitis: highly susceptible to bacterial superinfection (impetiginization)
- Immunosuppression (increases vulnerability to all infections)
- Overcrowding, such as in schools, nurseries, and communal living settings, significantly facilitate transmission, particularly of impetigo
Symptoms
Impetigo
Impetigo is the most common bacterial skin infection in children and presents in two distinct clinical forms:
Bullous Impetigo
- Caused predominantly by Staphylococcus aureus (toxin-producing strains)
- Characterized by bullae, raised fluid-filled skin lesions larger than 0.5 cm in diameter with clear content
- Bullae are surrounded by an erythematous (reddened) halo
- Upon rupture, bullae release purulent exudate that dries to form yellowish-honey-colored crusts
- May affect palms and soles (unlike the non-bullous form)
Non-Bullous Impetigo
- The most common form, accounting for approximately 70% of all impetigo cases
- Caused primarily by Streptococcus pyogenes and other organisms
- Characterized by vesicles, small raised lesions less than 0.5 cm in diameter containing clear fluid
- Similar evolution to the bullous form: rupture → purulent exudate → golden-yellow crusts
- Palms and soles are typically spared
Commonly affected body areas include:
- Face (especially around the mouth and nose)
- Limbs
- Trunk
- Areas around body orifices (oral cavity, nostrils, anal region)
Clinical note: Skin areas affected by scabies infestation or atopic dermatitis are particularly susceptible to impetiginization, a secondary bacterial infection superimposed on a pre-existing skin condition.
Whitlow (Paronychia)
Whitlow (also known as paronychia) is a staphylococcal infection of the nail fold, typically occurring as a secondary complication of minor local trauma (e.g., nail biting, hangnails, manicure injuries, splinters).
Clinical features include:
- Erythema (redness) of the skin surrounding the nail
- Edema (swelling) of the periungual tissue
- Pain and tenderness, often throbbing in nature
- Formation of a subcutaneous pus pocket with possible spontaneous discharge of purulent material
The condition can affect both fingernails and toenails and, if left untreated, may progress to involve deeper structures of the finger (felon, osteomyelitis).
Folliculitis
Folliculitis is a superficial infection of the hair follicle, characterized by:
- Pustules: raised skin lesions with purulent (pus-containing) fluid (no vesicles or bullae)
- Lesions are centered on a hair shaft and localized around the follicular opening
- No bulla formation in the superficial form
Commonly affected areas:
- Beard area (sycosis barbae in adult men)
- Scalp
- Limbs
In women who regularly practice hair removal by waxing or shaving, particularly during summer months, extensive folliculitis of the entire lower limbs is a well-recognized presentation, driven by the mechanical disruption of follicular epithelium combined with heat and humidity.
Diagnosis
Diagnosis of pyoderma is primarily clinical, based on careful physical examination of the skin lesions.
Differential diagnosis is important and should consider:
- Autoimmune bullous diseases (e.g., pemphigus vulgaris, bullous pemphigoid): rare in childhood but must be excluded; bullae in these conditions contain clear, sterile fluid
- Amicrobial pustuloses such as psoriasis: characterized by sterile pustules without bacterial involvement
- Scabies: may closely mimic impetigo, particularly when secondarily infected
- Atopic dermatitis with superinfection
When the diagnosis is uncertain, or when first-line treatment fails to produce improvement, microbiological cultures of pustular or blister fluid can identify the causative organism and guide targeted antibiotic selection.
Prognosis and Complications
The prognosis for uncomplicated superficial pyodermas is generally excellent, especially with timely diagnosis and appropriate treatment.
Common Complication: Autoinoculation
The most frequent complication is spread of bacteria via the hands, leading to autoinoculation of S. aureus to other body areas. This underscores the importance of hand hygiene and avoiding touching or scratching lesions.
Serious and Life-Threatening Complications
Although rare, the following toxin-mediated syndromes represent potentially fatal complications:
- Staphylococcal Toxic Shock Syndrome (TSS)
- Staphylococcal Scalded Skin Syndrome (SSSS) (staphylococcal epidermal necrolysis)
- Streptococcal Toxic Shock-Like Syndrome
These severe syndromes result from the systemic release of bacterial toxins and present with:
- High fever
- Nausea and vomiting
- Diarrhea
- Muscle pain and joint pain
- Widespread erythematous macular-papular rash and blistering
- Multi-organ involvement (shock)
Prognosis of toxin-mediated syndromes: These conditions have a rapid and potentially fatal course. Death may result from systemic infection spread (sepsis) and electrolyte disturbances caused by massive fluid and mineral loss through the skin. Mortality reaches 30–40% in severe cases, emphasizing the need for immediate hospitalization and intensive care.
Treatment and Remedies
Topical Treatment (First-Line for Superficial Infections)
For mild-to-moderate superficial pyodermas, local treatment is usually sufficient:
- Cleansing and antisepsis: Careful cleaning and disinfection of lesions using antiseptic solutions (e.g., chlorhexidine-based products)
- Topical antibiotics applied for 7–10 days:
- Fusidic acid
- Mupirocin (particularly effective against S. aureus, including MRSA strains)
- Clindamycin
- Erythromycin
Wound Dressing
In extensive cases, covering lesions with sterile gauze, cotton dressings, or sterile cloths helps isolate the infection and prevent autoinoculation.
Important: Avoid any dressing that may cause skin maceration (moisture retention). Do not apply adhesive plasters directly onto affected skin, as this promotes the development of new lesions.
Systemic (Oral) Antibiotic Therapy
Oral antibiotics are indicated when:
- Lesions are widespread or severe
- The patient is immunocompromised
- There is inadequate or partial response to topical treatment
- Signs of systemic involvement or shock are present (in which case intravenous therapy is mandatory and must be initiated as soon as possible)
Antibiotic classes used include:
- Beta-lactams: Penicillin (for streptococcal infections), penicillinase-resistant penicillins (e.g., flucloxacillin for staphylococcal infections)
- Cephalosporins: 1st, 2nd, and 3rd generation
- Macrolides (e.g., azithromycin, clarithromycin). Useful in penicillin-allergic patients.
- Fluoroquinolones
- Aminoglycosides
Systemic antibiotic therapy has the additional advantage of eradicating extracutaneous bacterial foci, thereby preventing distant septic complications.
Prevention
Prevention of S. aureus skin infections in high-risk individuals, such as patients scheduled for surgery or healthcare workers, can be achieved through:
- Intranasal application of mupirocin gel or ointment: This intervention decolonizes nasal carriers of S. aureus, providing protection for approximately 3 months
- Strict hand hygiene: Regular, thorough handwashing with soap and water or alcohol-based hand sanitizers
- Avoiding sharing personal items (towels, razors, clothing) in household or community settings
- Prompt treatment of minor skin wounds to prevent bacterial entry
- Management of underlying conditions such as atopic dermatitis, which significantly increase susceptibility to bacterial superinfection
- Appropriate hair removal techniques: minimizing trauma, using clean equipment, and applying antiseptic products before and after hair removal in susceptible individuals
Sources and Bibliography
- Cainelli T., Giannetti A., Rebora A. Manuale di dermatologia medica e chirurgica. McGraw-Hill, 4th edition.
- Saurat J., Grosshans E., Laugier P., Lachapelle J. Dermatologia e malattie sessualmente trasmesse. Italian edition edited by Girolomoni G. and Giannetti A. 3rd edition, 2006. Masson.
- Stevens DL, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2014;59(2):e10–e52.
- Gould FK, et al. Guidelines (2008) for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the United Kingdom. J Antimicrob Chemother. 2009;63(5):849–861.
- Koning S, et al. Interventions for impetigo. Cochrane Database Syst Rev. 2012.
