Skin and Soft Tissue Infections Flashcards
Cellulitis
Inflammation of the skin and subcutaneous tissues due to infection and involves deeper dermis and subcutaneous fat
Erysipelas
Inflammation due to infection that involves the upper dermis and superficial lymphatics
What are the clinical signs of cellulitis?
Signs are variable but can include:
- Redness
- Warmth
- Swelling
- Pain
- Fever
What is the cause of cellulitis?
Break in the skin leading to penetration and entry of pathogens
What are some risk factors of cellulitis?
– Edema / water retention – Skin conditions – Immunosuppression – Diabetes – Trauma
What are the most common pathogens in cellulitis?
- Strep pyogenes
- Staph aureus (both MSSA and MRSA)
Uncommon causes due to Gram negatives and bacteria from cat, dog and human bites.
How are Strep organized?
Chains
How are Staph organized?
Clusters
Purulent Cellulitis
Cellulitis associated with purulent drainage or exudate in absence of drainable abscess
What pathogen is purulent cellulitis common with?
MRSA
Non-purulent Cellulitis
Cellulitis with no purulent drainage, exudate, abscess
What pathogens are non-purulent cellulitis common with?
- Strep
- MSSA
What gives S. aureus methicillin resistance?
mecA gene
- it produces the pencillin binding protein 2a which binds to beta lactam antibiotics and confers resistance as it prevents the ringlike structure of penicillin‐like antibiotics to bind to the enzymes that help form the cell wall of the bacterium
What distinguishes CA from HA MRSA infections?
The SCCmec gene is different between the organisms
What are the risk factors for diabetic foot ulcers?
- Neuropathy • Poor sensation • Often leads to breaks in skin that go unnoticed - Peripheral vascular disease • Poor circulation
What are some complications of cellulitis?
- Sepsis
- Toxic Shock Syndrome
- Necrotizing Fasciitis
What is the presentation of Staph TSS?
- Fever
- Hypotension
- Diffuse macular rash
- Mutli-organ involvement
- Often negative blood cultures
What is the cause of Staph TSS?
TSS Toxin-1 is released which is a super antigen, causing activation of a large number of T cells and massive cytokine production/release
What is the cause of Strep TSS?
Exotoxin A and B are released which act as super antigens
What is the presentation of Strep TSS?
- Localized pain
- Swelling
- Erythema
- Fever
- Altered mental status
- Positive blood cultures
Diffuse erythematous rash in only 10%
Necrotizing Fasciitis
Deep seated infection of subcutaneous tissue, with destruction of fascia and fat.
What are the bacteria in Type I necrotizing fasciitis?
Polymicrobial with both aerobic/anerobic
What are the bacteria in Type II necrotizing fasciitis?
Group A Strep or MRSA - mono bacterial
What are the clinical signs of necrotizing fasciitis?
- Pain out of proportion to the exam
- Rapidly evolving symptoms
- Fever
- Minimal skin changes
Impetigo
Superficial bacterial infection, contagious
What is the common presentation of impetigo?
Seen in children on the face
What are the main pathogens causing impetigo?
- Group A Strep
- S. aureus
What bacteria is common with cat bites?
Pasteurella
What patients are at severe risk of sepsis from dog and cat bites due to Capnocytophaga canimorsus?
Asplenic patients
A 45 yr old woman was bitten on her right hand by her house cat during some aggressive play. There was a small amount of bleeding from 2 puncture wounds on the palm, which were promptly washed. 1 day later, she developed erythema at the wound site, which immediately spread circumferentially. The wound is now painful and she has subjective chills. PE: T37.2, HR: 102, BP: 160/100. There is swelling, erythema and tenderness at the thenar eminence of the R hand with irregular spreading of erythema that is now proximal to the wrist. Nondraining puncture marks are evident.
- A. E.coli
- B. Pasteurella multocida
- C. Candida albicans
- D. Eikenella corrodens
• B. Pasteurella multocida
A 25 yr old man is evaluated for pain and swelling of his R hand. 3 days ago he was involved in an altercation during which he punched another man in the mouth with his R fist. On PE: T: 38.3, BP; 124/84. R hand is painful, with swelling over the 2nd MCP joint with decreased ROM. Aspiration of the joint reveals a small amount of purulent material.
- A: Eikenella corrodens
- B. Capnocytophaga canimorsus
- C. Pasteurella multocoda
- D. Candida albicans
- E. Pseudomonas auerginosa
• A: Eikenella corrodens
What are some risk factors for Pseudomonas infections?
- After burns
- Trauma
- Folliculitis from hot tubs
