Infections of the Skin, Muscles, and SoftTissues¶
Chapter 134 | Harrison's 22e · Part 5 – Infectious Diseases: Bacterial · Chapter 134
Key Clinical Points¶
- Skin and soft tissue infections occur globally but have increased due to factors like MRSA emergence (specifically the USA300 clone), global travel, and trauma from natural disasters or combat.
- The dermal papillary capillary network is a critical anatomical site for localizing infection and facilitating systemic spread via postcapillary venules.
- Erysipelas is characterized by rapid superficial spread through lymphatics, resulting in flaccid edema.
- Necrotizing fasciitis is a critical infection requiring urgent recognition; key indicators include pain out of proportion to findings and signs of vascular compromise (e.g., purple bullae, ecchymosis).
- Vesicle formation can occur in viral infections (varicella, herpes zoster) or bacterial infections (ecthyma gangrenosum).
- Myonecrosis is characterized by rapid progression with gas formation visible on imaging.
- Rickettsialpox presents with a characteristic eschar with an erythematous halo and regional lymphadenopathy.
- Blistering dactylitis involves vesicular infection of distal digits, typically caused by S. aureus or group A streptococcus.
1. EPIDEMIOLOGY & GLOBAL TRENDS¶
Skin and soft tissue infections occur universally but have increased due to:
• Global microbial dissemination via air travel and acquisition of antibiotic resistance • Increased natural disasters causing trauma • Combat-related injuries facilitating pathogen access
Hospital Admissions: Increased by 27% between 2000–2004, largely attributed to the emergence of the USA300 MRSA clone.
2. ANATOMIC RELATIONSHIPS & PATHOPHYSIOLOGY¶
The dermal papillary capillary network plays critical roles:
• Provides nutrition to the stratum germinativum • Produces clinical signs (e.g., petechiae, Osler nodes) in endocarditis • Facilitates systemic spread via postcapillary venules
Barrier Dynamics: • Disruption of the stratum corneum barrier allows bacterial translocation. • Hair follicles serve as portals for both normal flora and extrinsic pathogens.
3. CLINICAL FEATURES & PATHOLOGY¶
Infections Associated with Vesicles:
• Varicella: Centripetal rash with dewdrop vesicles on trunk and extremities. • Herpes zoster: Unilateral dermatomal distribution with prodromal pain. • Herpes simplex (HSV): Oral or genital lesions; common recurrences. • Molluscum contagiosum: Flaccid vesicles, typically in immunocompromised individuals.
Deep Tissue Infections:
• Necrotizing fasciitis: Characterized by pain out of proportion to findings and signs of vascular compromise (e.g., purple bullae, ecchymosis). • Myonecrosis: Rapid progression with gas formation on imaging. • Rickettsialpox: Eschar with erythematous halo and regional lymphadenopathy. • Blistering dactylitis: Vesicular infection of distal digits by S. aureus or group A streptococcus.
Summary of Common Skin Infections (Table 134-1):
• Vesicles: Varicella, Herpes zoster, HSV, Molluscum contagiosum. • Crusted Lesions: Impetigo contagiosa (S. pyogenes), Bullous impetigo/ecthyma (S. aureus), Ringworm (fungal), Sporotrichosis, Histoplasmosis, Coccidioidomycosis, Blastomycosis, Cutaneous leishmaniasis, Nocardiosis. • Papular and Nodular Lesions: Verruca vulgaris, Condylomata acuminata, Lepromatous leprosy, Syphilis (primary/secondary/tertiary), Erysipelas (S. pyogenes).
4. DIAGNOSTIC APPROACH¶
- Erysipelas: Identify rapid superficial spread and flaccid edema, which indicates lymphatic obstruction.
- Necrotizing Infections: ◦ Recognize clinical red flags: pain out of proportion to findings and signs of vascular compromise (purple bullae). ◦ Confirm with imaging: CT scan to identify subcutaneous gas and muscle necrosis.
- Herpes zoster: Identify unilateral dermatomal distribution and prodromal pain.
- Rickettsialpox: Identify characteristic eschar with erythematous halo and regional lymphadenopathy.
5. MANAGEMENT & TREATMENT¶
- Animal Bite: ◦ Prophylaxis or Early Infection:
- Amoxicillin–clavulanate (875/125 mg PO bid)
- Doxycycline (100 mg PO bid)
- IV options: Ampicillin–sulbactam (1.5–3 g IV q6h) OR Clindamycin (600–900 mg IV q8h) plus Ciprofloxacin (400 mg IV q12h) or cefoxitin (2 g IV q6h) ◦ Established Infection:
- Ampicillin–sulbactam (1.5–3 g IV q6h)
- Clindamycin (600–900 mg IV q8h) plus Ciprofloxacin (400 mg IV q12h) or cefoxitin (2 g IV q6h)
- Bacillary Angiomatosis: ◦ Antibiotics: Erythromycin (500 mg PO qid) or Doxycycline (100 mg PO bid) ◦ Antivirals: Acyclovir (400 mg PO tid for 10 days), Famciclovir (250 mg PO tid for 5–10 days), or valacyclovir (1000 mg PO bid for 10 days)
- Herpes Zoster (Immunocompetent host >50 years): ◦ Antivirals: Acyclovir (800 mg PO 5 times daily for 7–10 days), Famciclovir (500 mg PO tid for 7–10 days), or valacyclovir (1000 mg PO tid for 7 days) ◦ Antibiotics: Nafcillin or oxacillin (2 g IV q4–6h), Cefazolin (1–2 g q8h), ampicillin/sulbactam (1.5–3 g IV q6h), erythromycin (0.5–1 g IV q6h), or clindamycin (600–900 mg IV q8h)
- MRSA Skin Infection: ◦ Primary Options: Vancomycin (1 g IV q12h) or Linezolid (600 mg IV q12h) ◦ Combination Options:
- Clindamycin (600–900 mg IV q6–8h) plus penicillin G (4 million units IV q4h)
- Clindamycin (600–900 mg IV q6–8h) plus a cephalosporin (first- or second-generation)
- Necrotizing Fasciitis (Mixed Aerobes and Anaerobes): ◦ Option A: Ampicillin (2 g IV q4h) + clindamycin (600–900 mg IV q6–8h) + ciprofloxacin (400 mg IV q6–8h) ◦ Option B: Vancomycin (1 g IV q6h) + metronidazole (500 mg IV q6h) + ciprofloxacin (400 mg IV q6–8h) ◦ Alternative Options:
- Clindamycin (600–900 mg IV q6–8h) plus penicillin G (4 million units IV q4h)
- Clindamycin (600–900 mg IV q6–8h) plus cefoxitin (2 g IV q6h)
KEY PEARLS & HIGH-YIELD POINTS¶
• Necrotizing Fasciitis: A medical emergency; pain out of proportion to physical findings is a hallmark. CT imaging is critical for identifying gas and muscle necrosis. • Capillary Network: The dermal papillary capillary network is the primary site for both local inflammatory responses and systemic spread via postcapillary venules. • MRSA Impact: The emergence of the USA300 clone has significantly increased hospital admissions for skin infections. • Erysipelas: Characterized by rapid superficial spread and flaccid edema due to lymphatic obstruction.
Reference Tables¶
TABLE 134-1 Skin and Soft Tissue Infections¶
Harrison's 22e, p.1050
| LESION, CLINICAL SYNDROME | INFECTIOUS AGENT(S) | SEE ALSO CHAP(S). |
|---|---|---|
| Vesicles | ||
| Smallpox | Variola virus | S4 |
| Chickenpox | Varicella-zoster virus | 198 |
| Shingles (herpes zoster) | Varicella-zoster virus | 198 |
| Cold sores, herpetic whitlow, herpes gladiatorum | Herpes simplex virus | 197 |
| Hand-foot-and-mouth disease | Coxsackievirus A16 | 210 |
| Orf | Parapoxvirus | 201 |
| Molluscum contagiosum | Molluscum contagiosum poxvirus | 201 |
| Rickettsialpox | Rickettsia akari | 192 |
| Blistering distal dactylitis | Staphylococcus aureus or Streptococcus pyogenes | 152, 153 |
| S. aureus S. pyogenes, Clostridium spp., mixed aerobes and anaerobes Clostridium spp. Vibrio vulnificus |
||
| Crusted lesions | ||
| Bullous impetigo/ecthyma | S. aureus | 152 |
| Impetigo contagiosa | S. pyogenes | 153 |
| Ringworm | Superficial dermatophyte fungi | 225 |
| Sporotrichosis | Sporothrix schenckii | 225 |
| Histoplasmosis | Histoplasma capsulatum | 218 |
| Coccidioidomycosis | Coccidioides immitis | 219 |
| Blastomycosis | Blastomyces dermatitidis | 220 |
| Cutaneous leishmaniasis | Leishmania spp. | 233 |
| Cutaneous tuberculosis | Mycobacterium tuberculosis | 183 |
| Nocardiosis | Nocardia asteroides | 179 |
| S. aureus Pseudomonas aeruginosa Schistosoma spp. Propionibacterium acnes |
||
| Papular and nodular lesions | ||
| Fish-tank or swimming-pool granuloma | Mycobacterium marinum | 185 |
| Creeping eruption (cutaneous larva migrans) | Ancylostoma braziliense | 238 |
| Dracunculiasis | Dracunculus medinensis | 240 |
| Cercarial dermatitis | Schistosoma mansoni | 241 |
| Verruca vulgaris | Human papillomaviruses 1, 2, 4 | 203 |
| Condylomata acuminata (anogenital warts) | Human papillomaviruses 6, 11, 16, 18 | 203 |
| Onchocerciasis nodule | Onchocerca volvulus | 240 |
| Cutaneous myiasis | Dermatobia hominis | 472 |
| Verruca peruana | Bartonella bacilliformis | 177 |
| Cat-scratch disease | Bartonella henselae | 177 |
| Lepromatous leprosy | Mycobacterium leprae | 184 |
| Secondary syphilis (papulosquamous and nodular lesions, condylomata lata) | Treponema pallidum | 187 |
| Tertiary syphilis (nodular gummatous lesions) | T. pallidum | 187 |
| Bacillus anthracis Francisella tularensis Yersinia pestis Mycobacterium ulcerans M. leprae M. tuberculosis Haemophilus ducreyi T. pallidum |
||
| Erysipelas | S. pyogenes | 153 |
| Staphylococcus spp., Streptococcus spp., various other bacteria |
||
| Necrotizing fasciitis | ||
| Streptococcal gangrene | S. pyogenes | 153 |
| Fournier gangrene | Mixed aerobic and anaerobic bacteria | 182 |
| Staphylococcal necrotizing fasciitis | Methicillin-resistant S. aureus | 152 |
| S. aureus S. pyogenes Clostridium spp. Mixed aerobic and anaerobic bacteria Mixed aerobic and anaerobic bacteria |
TABLE 134-2 Treatment of Common Infections of the Skin DIAGNOSIS/CONDITION Animal bite (prophylaxis or early infection)…¶
Harrison's 22e, p.1054
| DIAGNOSIS/CONDITION | PRIMARY TREATMENT | ALTERNATIVE TREATMENT | SEE ALSO CHAP(S). |
|---|---|---|---|
| Animal bite (prophylaxis or early infection)a |
Amoxicillin–clavulanate (875/125 mg PO bid) |
Doxycycline (100 mg PO bid) | 146 |
| Ampicillin–sulbactam (1.5–3 g IV q6h) | Clindamycin (600–900 mg IV q8h) plus Ciprofloxacin (400 mg IV q12h) or cefoxitin (2 g IV q6h) |
||
| Bacillary angiomatosis | Erythromycin (500 mg PO qid) | Doxycycline (100 mg PO bid) | 177 |
| Acyclovir (400 mg PO tid for 10 days) | Famciclovir (250 mg PO tid for 5–10 days) or valacyclovir (1000 mg PO bid for 10 days) |
||
| Herpes zoster (immunocompetent host >50 years of age) |
Acyclovir (800 mg PO 5 times daily for 7–10 days) |
Famciclovir (500 mg PO tid for 7–10 days) or valacyclovir (1000 mg PO tid for 7 days) |
198 |
| Nafcillin or oxacillin (2 g IV q4–6h) | Cefazolin (1–2 g q8h) or ampicillin/sulbactam (1.5–3 g IV q6h) or erythromycin (0.5–1 g IV q6h) or clindamycin (600–900 mg IV q8h) |
||
| MRSA skin infectiond | Vancomycin (1 g IV q12h) | Linezolid (600 mg IV q12h) | 152 |
| Clindamycin (600–900 mg IV q6–8h) plus penicillin G (4 million units IV q4h) |
Clindamycin (600–900 mg IV q6–8h) plus a cephalosporin (first- or second-generation) |
||
| Necrotizing fasciitis (mixed aerobes and anaerobes) |
Ampicillin (2 g IV q4h) plus clindamycin (600–900 mg IV q6–8h) plus ciprofloxacin (400 mg IV q6–8h) |
Vancomycin (1 g IV q6h) plus metronidazole (500 mg IV q6h) plus ciprofloxacin (400 mg IV q6–8h) |
182 |
| Clindamycin (600–900 mg IV q6–8h) plus penicillin G (4 million units IV q4–6h) |
Clindamycin (600–900 mg IV q6–8h) plus cefoxitin (2 g IV q6h) |