DERM 08: Skin and Soft Tissue Infections (SSTIs) Flashcards
1
Q
What are skin and soft tissue infections (SSTIs)?
A
- common infections
- incidence unknown
- increasing frequency – invasive infections, drug-resistant infections
2
Q
What is the pathophysiology of SSTIs?
A
- skin and soft tissue infections may involve any or all layers of skin, fascia, and muscle
- may spread from initial site of infection → complications (sepsis, endocarditis)
3
Q
What are the predisposing factors for SSTIs?
A
- high concentration of bacteria on skin (> 105 CFUs)
- excessive moisture
- inadequate blood supply
- availability of bacterial nutrients
- damage to skin layers allowing for bacterial penetration
4
Q
What are the normal skin flora?
A
bacteria:
- gram-positive: coagulase-negative staphylococci, micrococci, corynebacterium species (diptheroids), propionibacterium species
- gram-negative: acinetobacter species
fungi:
- malassezia species
- candida species
5
Q
What are the causative pathogens of SSTIs?
A
gram-positive bacteria – most common
- staph aureus
- coagulase-negative staphylococci (CoNS)
- diptheroids
- strep pyogenes (group A strep)
gram-negative bacteria – less common
- E. coli
- enterobacteriacae
- acinetobacter
6
Q
What are the 4 classes of STIs and their management/treatment options?
A
class 1: afebrile, otherwise healthy
- management: outpatient, oral/topical antibiotics
class 2: febrile, ill-appearing, no unstable comorbidities
- management: outpatient or short hospitalization, oral or IV antibiotics
class 3: toxic appearance, ≥ 1 co-morbidity
- management: hospitalization, IV antibiotics
class 4: sepsis or life-threatening infection
- management: hospitalization, IV antibiotics +/- surgery
7
Q
What are the goals of therapy for SSTIs?
A
- eradication of infection (if possible)
- prevention of complications
- prevent/minimize adverse drug reactions
8
Q
What is impetigo?
A
- superficial skin infection
- common in children (age 2-5 years), and during hot/humid weather
- contagious – transmitted from person to person
- non-bullous and bullous forms
9
Q
What are the risk factors for impetigo?
A
- warm, humid weather
- close contact environments (ie. daycare)
- anything that breaks integrity of skin – burns, cuts or scrapes, bug bites, eczema
10
Q
What are the signs and symptoms of impetigo?
A
- red rash with vesicles
- vesicles rupture → ooze for few days → golden or honey-coloured crust
- mild pruritis (itchiness)
11
Q
What is non-bullous impetigo?
A
- most common form
- papules → vesicles (w/ erythema) → pustules → thick crusts (golden appearance)
- evolution occurs over 1 week
- lesions < 1.5 cm in diameter
- usually face and extremities
- multiple lesions but localized
- mild tenderness, itchiness
12
Q
What pathogen results in non-bullous impetigo?
A
staph aureus, strep pyogenes
13
Q
What is bullous impetigo?
A
- primarily seen in young children
- papules → vesicles → flaccid bullae with clear yellow fluid → bullae with darker, pus fluid → rupture → thin brown crust
- lesions > 1.5 cm in diameter
- trunk usually affected, and groin, armpits, skin folds can be infected
- fewer lesions than non-bullous
14
Q
What pathogen results in bullous impetigo?
A
staph aureus
- produces toxin A → exfoliation (causes loss of cell adhesion in epidermis)
15
Q
What is ecthyma?
A
- ulcerative form of impetigo
- lesions epidermis → dermis
- ‘punched-out’ ulcers covered with yellow crust and purple borders
16
Q
What pathogen results in ecthyma?
A
staph aureus (most common), strep pyogenes
17
Q
What are the non-pharmacological measures for impetigo?
A
- crust removal – gentle washing (clean warm water, mild soap)
- saline compresses – apply for 10 minutes, 3-4x per day
18
Q
How can the transmission of impetigo be prevented?
A
- wash hands
- cover draining lesions with clean, dry dressings
- avoid scratching lesions
- keep fingernails short
- avoid sharing towels
- wash patient’s clothes and linens separately from rest of laundry
19
Q
What is the treatment for mild impetigo (children and adults)?
A
- limited number of lesions
- can use ‘wait and see’ approach
- minor ailments prescribing in BC
- antibiotics – shorten duration, speed healing
- mupirocin 2% ointment to lesions TID
- fusidic acid 2% cream to lesions TID – increase resistance
- duration: 5 days
- topical antibiotics as effective as oral antibiotics for mild impetigo
20
Q
What is the treatment for moderate to severe impetigo (children)?
A
cephalexin 15-25 mg/kg/dose PO q6h (max 500 mg/dose)
- avoid cloxacillin due to taste, unless child can swallow capsules
if suspected MRSA or cephalexin/cloxacillin allergy:
- TMP/SMX 4 mg/kg/dose (TMP component) PO BID
- doxycycline 2 mg/kg/dose PO q12h
- clindamycin 13 mg/kg/dose PO TID – avoid due to taste unless child can swallow capsules
duration: 7 days
21
Q
What is the treatment for moderate to severe impetigo (adults)?
A
- cephalexin 250 mg PO QID
- cloxacillin 250 mg PO QID
if suspected MRSA or cephalexin/cloxacillin allergy:
- clindamycin 450 mg PO TID
- TMP/SMX 1 DS tablet (160/800 mg) PO BID
- doxycycline 100 mg PO BID
duration: 7 days
22
Q
When should impetigo be referred to a physician/NP?
A
- age < 1 year
- fever or chills
- malaise or fatigue
- immunocompromised
- recurrent episodes (ie. > 2 distinct episodes in past 6 months)
- history of valvular heart disease
- ‘extensive disease’ (moderate-severe) – > 2 affected areas (numerous lesions) or ‘widespread’ erythema
- bullous impetigo (even if considered mild)
23
Q
What is the pathophysiology of cellulitis?
A
- initially affects epidermis and dermis
- may spread to superficial fascia
- serious disease – may spread through lymphatic system to blood
24
Q
What are the signs and symptoms of cellulitis?
A
- fever, chills, malaise
- area feels hot and painful
- erythema and edema
- non-elevated and poorly marginated lesions
- warm to touch
- inflammation
- tender lymphadenopathy
- lab tests: blood cultures, wound cultures
25
What are the risk factors for cellulitis?
- IV drug use
- diabetes mellitus
- wounds – minor trauma, abrasion, ulcer, surgical sites
- vascular insufficiency
26
What are the likely pathogens of cellulitis?
- group A streptococci
- staph aureus
- occasionally other gram-positive cocci
- gram-negative bacilli
- anaerobes
27
What is the treatment for mild to moderate cellulitis?
- cloxacillin 500 mg PO QID
- cephalexin 500 mg PO QID
penicillin and cephalexin allergy:
- clindamycin 150-300 mg PO TID
duration: 7-10 days
28
What is the treatment for moderate to severe cellulitis?
- cloxacillin 1-2g IV q6h
- cefazolin 1-2 g IV q8h
duration: 10 days
29
What is the treatment for cellulitis if MRSA is suspected?
- vancomycin 1 g IV q8-12h (or 15 mg/kg IV q8-12h) – target trough level 10-15 mg/L
- clindamycin 600 mg IV q8h
duration: 10 days
30
What is necrotizing fasciitis?
- life-threatening infection
- subcutaneous tissue → destruction of superficial fascia and subcutaneous fat
31
What are the signs and symptoms of necrotizing fasciitis?
- fever, chills, shock, pain
- affected area is hot, swollen, erythematous without sharp margins
- shiny, very tender
- swelling, bullae
- lab tests: WBC + diff, surgical tissue samples, blood cultures, tissue cultures
32
What is type 1 necrotizing fasciitis?
- after trauma and/or surgery
- slower spread of infection
- synergistic destruction of fat and fascia
- polymicrobial: anaerobes (bacteroides, peptostreptococcus), streptococci, enterobacteriacae
33
What is the treatment for type 1 necrotizing fasciitis?
vancomycin 20 mg/kg IV q __h + piperacillin/tazobactam 4.5g IV q6H
- interval for vancomycin depends on renal function
duration: 10-14 days
34
What is type 2 necrotizing fasciitis?
flesh-eating disease
- minor trauma or injury
- fast spread of infection
- necrosis of subcutaneous tissues and skin
- early onset shock and multi-organ failure
- virulent strain of strep pyogenes
- mortality 20-50%
35
What is the treatment for type 2 necrotizing fasciitis?
penicillin 4 MU IV q4h + clindamycin 600 mg IV q8h (combination therapy)
- severe group A strep infections
- production of streptococcal pyrogenic exotoxins
- penicillin: cell wall agent
- clindamycin: inhibits protein synthesis (exotoxin production)
- no synergy or antagonistic effects
duration: 10-14 days
36
What are dog bites?
- 80% all animal bite wounds
- approximately 70% on extremities
- infection rates: 10-20%
37
What are cat bites?
- 5-15% of all animal bite wounds
- most common on upper extremities
- infection rates: 30-80%
38
What are human bites?
- 3rd most frequent type of bite
- bites or blows to mouth (clenched fist injuries)
- more serious and more prone to infection
- infectious complications: 10-50%
- all bite wounds should be irrigated thoroughly
39
What are the pathogens of dog bites?
same as cat bites
- pasteurella multocida, staph aureus, streptococci, anaerobes
40
What are the pathogens of cat bites?
same as dog bites
- pasteurella multocida, staph aureus, streptococci, anaerobes
41
What are the pathogens of human bites?
eikenella corrodens, staph aureus, streptococci, corynebacterium species, bacteroides species, peptostreptococcus species
42
When should prophylaxis for cat bites be done?
all ‘significant’ cat bites within 12 hours because of high rate of infection
43
When should prophylaxis for dog bites be done?
same as human bites
- moderate/severe
- crush injury/edema
- age > 50 years
- puncture wounds
- bone/joint involvement
- injuries to hand, foot, face, genitalia
- splenectomized patients
- immunocompromised patients
44
When should prophylaxis for human bites be done?
same as dog bites
- moderate/severe
- crush injury/edema
- age > 50 years
- puncture wounds
- bone/joint involvement
- injuries to hand, foot, face, genitalia
- splenectomized patients
- immunocompromised patients
45
What is the drug therapy for prophylaxis for bite wounds?
- amoxicillin-clavulanate 500 mg PO TID or 875 mg PO BID
- beta-lactam allergy: doxycycline 100 mg PO BID
- duration: 3-5 days
46
What is the treatment for bite wounds?
- irrigation and debridement
- tetanus vaccine
- amoxicillin-clavulanate 500 mg PO TID or 875 mg PO BID
penicillin allergy:
- doxycycline 100 mg PO BID
- clindamycin 300 mg PO QID + ciprofloxacin 500 mg PO BID
- cefuroxime axetil 500 mg PO BID
duration 7-10 days
47
What is the treatment for more severe bite wounds?
IV drug therapy:
- piperacillin-tazobactam 3.375 g IV q6h
- meropenem 500 mg IV q6h (or imipenem)
duration 10-14 days
48
Summary
What are the majority of exanthems caused by?
caused by viruses, and resolve on their own
49
Summary
What are the majority of SSTIs caused by?
caused by gram-positive bacteria
50
What are some complications of SSTIs?
- septic arthritis
- osteomyelitis
