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Skin and Soft Tissue Infections Flashcards

1
Q

Describe cellulitis and the most common causative organisms.

A

Bacteria breach the skin barrier and infect and spread throughout the deeper dermis and fat

  • characterised by oedema, erythema and warmth
  • most common in the lower extremities
  • S.aureus, beta-haemolytic streptocci (A, B, C and G)
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2
Q

Which group of people are most likely to get cellulitis?

A

Middle aged and elderly people

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3
Q

Where does S.aureus normally live?

A

Carried by 30-40% of normal people, in the nose or moist areas of the skin
Type carried is stable
2% MRSA prevalence

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4
Q

What and where is the average carriage of strep pyogenes?

A

5-15% carriage

Normally in the respiratory tract and vaginal tract

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5
Q

What are the non-modifiable risk factors for cellulitis?

A 
Pregnancy
White caucasian 
Trauma
Animal/insect bites
Tattoos
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6
Q

What are the modifiable risk factors for cellulitis?

A 
Venous insufficiency
Lymphoedema
Ulcers
Eczema
Athletes foot
Burns
Surgery
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7
Q

What factors are incorporated when considering the management decisions in SSTI?

A

Severity
Anatomical site
Health Care Associate Infections
Co-morbidities

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8
Q

When deciding between treating at home or treating in the community, what criteria mean they have to remain in hospital?

A 
Severe, localising pain
Confusion
Rapidly evolving skin lesions or skin blistering 
Systolic blood pressure  <100mmHg
Sepsis syndrome 
- heart rate >100
- RR >20/min
- temp >38 or <36
- WCC >12 or <4/mm3
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9
Q

Describe a class 1 soft tissue/skin infection.

A

No sign of systemic toxicity
No co-morbidities
Oral antibiotics
Treated as an outpatient

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10
Q

Describe a class 2 soft tissue/skin infection.

A

May have a systemic illness
Has PVD, obesity or venous insufficiency
IV antibiotics
Hospital treatment for at least 48 hours, then community treatment

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11
Q

Describe a class 3 soft tissue/skin infection.

A

Significant systemic illness
Unstable co-morbidities
IV antibiotics
Hospital treatment

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12
Q

Describe a class 4 soft tissue/skin infection.

A

Sepsis syndrome/necrotising fasciitis
Unstable co-morbidities
IV antibiotics and surgery
Hospital treatment

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13
Q

What is the organism and associated treatment for typical cellulitis?

A

S.pyogenes

- ampicillin or flucloxacillin

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14
Q

What is the organism and associated treatment for typical cellulitis with pus?

A

S.aureus (sometimes MRSA)

  • Flucloxacillin
  • Vancomycin
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15
Q

What is the treatment for typical cellulitis when the patient has a penicillin allergy?

A

Doxycycline
Clindamycin
or
Vancomycin

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16
Q

What is the organism and associated treatment for cellulitis caused by cat/dog bite?

A

Pasteurella multocida

  • co-amoxiclav
  • doxycycline and
  • metronidazole
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17
Q

What is the organism and associated treatment for cellulitis after fresh water exposure?

A

Aeromonas hydrophila

- ciprofloxacin

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18
Q

What is the organism and associated treatment for cellulitis after salt water exposure?

A

Vibrio vulnificus

- doxycycline

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19
Q

What is the organism and associated treatment for necrotising fasciitis?

A

C.perfringes/S.pyogenes

- flucloxacillin, clindamycin, gentamicin and metronidazole

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20
Q

What is the organism and associated treatment for cellulitis in butchers/fish handlers?

A

Erysipelothrix

- ciprofloaxacin

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21
Q

What are the differential diagnoses for cellulitis?

A

Stasis dermatitis - bilateral, circumfernetial
Acute arthritis - joint involvement
Pyoderma gangrenosum - ulceration on legs
Hypersensitivity - exposure to allergens, no fever or pain
DVT - no skin changes or fever
Necrotising fasciitis - severe pain, swelling, fever, rapid progression

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22
Q

What things should you consider when someone with cellulitis isn’t improving after treatment?

A

Resistance
Admission to hospital
Underlying conditions (bone infection, abscess, PVD)
Incorrect diagnosis (DVT, abscess, chronic changes)

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23
Q

What is the difference between cellulitis and erysipelas?

A

Cellulitis - bacterial infection of the lower layers of the skin
Erysipelas - bacterial infection of the upper layers of the skin, and superficial lymphatics
- raised lesion with clear line of demarcation

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24
Q

Describe what parts of the body erysipelas involves

A

Classically butterfly involvement of the face (20% of cases)
Legs are affected (80% of cases)
Can also involve the ear

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25
What are the most common causative organisms of erysipelas?
Group A strep - more rarely you can get B, C and G as well - staph aureus also a rare cause
26
How is erysipelas diagnosed?
Elevated ASOT for 10 days | Mainly a clinical diagnosis, based on how the skin looks
27
Describe the appearance of an impetigo skin infection.
Sores and blisters, commonly in a perioral location | - honey coloured
28
What causes an impetigo skin infection?
Highly transmissible staphylococcus infection of the epidermis
29
Who would an impetigo infection most commonly affect?
Children | Sports people
30
What is the treatment for an impetigo skin infection?
Gently remove the crust Treat with flucloxacillin - be aware of the risk of a secondary infection (e.g. HSV)
31
What is the definition of necrotising fasciitis?
Severe inflammation of the muscle sheath that leads to necrosis of the subcutaneous tissue and adjacent fascia
32
What bacteria (and virulence factors) cause necrotising fasciitis?
Most commonly a mixed infection (aerobes and anaerobes) | Toxin mediated - superantigens and cytokine release
33
What are the important differentiating factors between cellulitis and necrotising fasciitis?
``` Initial pain becomes painless Rapid spread Systematically unwell Dusky skin and necrosis May have skin crepitus ```
34
What are the clinical manifestations of necrotising fasciitis?
Rapid progression Most common on the extremities Initially erythema and swelling without shapr margins Pain and tenderness Lymphatic involvement is rare Colour change from red-purple to blue-grey Skin breakdown and bullae with development of anaethesia Probing of the lesion reveals easy through the tissues
35
Describe the management of necrotising fasciits.
Surgical debridement Antibiotics Activated protein C (evidence is limited and can't b used within 24 hours of surgery)
36
Which antibiotics are used in the management of necrotising fasciitis?
``` Penicillin Flucloxacillin Clindamycin Gentamicin Metronidazole ```
37
When is prophylactic treatment for bites needed?
If the bite is deep, on the hands or the patient is immunocompromised/ splenectomised
38
What is the treatment for a bite?
Gram stain of the wound and blood cultures Debridement and abscess drainage Antibiotics - cover staph, anaerobes, pasteurella and capnocytophaga Rabies immunoglobulin and vaccination is appropriate
39
Describe pasteurella and it's associated treatments.
``` Gram negative bacteria Most common pathogen which infects bites Treated with - penicillins - cephalosporins - tetracyclines - quinolones - macrolides Co-amoxiclav, doxycycline and metronidazole ```
40
Aeromonas species are associated with what clinical syndrome? - caught after exposure to fresh water
Rapidly developing infection with fever and sepsis
41
Edwardsiella tarda are associated with what clinical syndrome? - caught after exposure to fresh water
Cellulitis, occasionally fulminant infection with bacterameia
42
Erysipelothrix rhusiopathiae are associated with what clinical syndrome? - caught after puncture wounds from crabs
Indolent localised cutaneous eruption, erysipeloid
43
Vibrio vulnificus are associated with what clinical syndrome? - caught after exposure to salt or brackish water
Rapidly progressive necrotising infection, bullous, cellulitis, sepsis
44
Mycobacterium marinum are associated with what clinical syndrome? - caight after exposure to fresh or salt water
Indolent infection, papules to ulcers, ascending lesion may resemble sporotrichosis
45
What is tinea?
A superficial dermatophyte infections characterised by scaly, inflammatory or non-inflammatory patches - generally limited to the epidermis and expands in a centrifungal pattern
46
What is classification of tinea based off?
The affect region - tinea pedis for feet (athletes foot) - tinea corporis for the body - tinea capitis for head/scalp - tinea curis for groin (jock itch)
47
What is tinea caused by?
Dermatophytes - trichophyton (most common) - microsporum - epidermophyton
48
How is a tinae infection diagnosed?
Potassium hydroxide (KOH) preparation from a skin scraping
49
How is erythema infectiosum caused?
Parvovirus B19 | - transmission via respiratory droplets, blood or blood products
50
What are the symptoms of erythema infectiosum?
Fever Headache Runny nose Pruritic rash on the face (slapped cheek), torso and extremities
51
What are the complications of persistent erythema infectiosum?
``` Persistent arthropathy Gloves-and-socks syndrome Papular, purpuric eruptions on the hands and feet Acute cessation of RBC production - transient aplastic crisis - chronic RBC aplasia - hydrops fetalis - congenital anaemia ```
52
What is hand-foot-and-mouth disease?
A viral illness with oral and sital-extremitry lesions
53
What is the cause of hand-and-foot-and-mouth disease?
Coxsackie virus A16 | - typically affects children and infants
54
How can hand-foot-and-mouth disease cause and epidemic?
Highly contagious during the first week of the illness | - direct contact with nasal and oral secretions or faecal material
55
What are the symptoms of hand-foot-and-mouth disease?
``` Fever Rash Headache Sore throat Oropharyngeal ulcers Loss of appetite ```
56
How can herpes reoccur once it has been treated?
Virus doesn't disappear from the body, lives latent in the sensory never ganglia
57
What is the diagnosis and treatment for herpes simplex?
``` Clinical diagnosis - blood or vesicle fluid for PCR - serology - be careful as 60% of cases are asymptomatic Treatment - acyclovir (topical, oral or IV) ```
58
What two conditions can the varicella zoster virsu cause?
Chickenpox | Shingles
59
How is chicken pox diagnosed?
PCR of vesicle fluid (or serology)
60
Chickenpox is self-limiting in children; how is it problematic in adults?
Can cause congenital abnormalities during pregnany | Pneumonitis
61
If an at risk adult (pregnant, immunocompromised or has contracted penumonitis) contracts chickenpox, how are they treated?
Need to be treated within 48 hours of symptoms | - acyclovir PO/IV
62
Describe shingles.
Reactivation of dormant VZV (dorsal root ganglia) Dermatomal distribution Highly contagious until all the vesicles have crusted over
63
How is shingles treated?
Only the immunocompromised patients and those with disseminated infection are treated - acyclovir NSAIDs and gabapneitn for the pain
64
Briefly describe burns.
Damage to the skin (Heat, chemical, radiation, cold) causing protein denaturing
65
What conditions can occur because a burn has compromised resistance to the environment?
Infection - must be diagnosed clinically (burn swabs are rarely sterile) Hypothermia Acid-base abnormalities Dehydration
66
How are burns managed?
``` Dressings Topical antimicrobials (e.g. sulfadiazine, may delay re-epithelialisation) Topical antibiotics (bacitracin) Systemic antibiotics (directed by culture results) are required in invasive infection ```
67
What is staphylococcal scalded skin syndrome, and what are its symptoms?
Staph aureus strains producing an exfoliative exotoxin Widespread bullae formation and exfoliation - known as Ritter's disease or Pehmphigus neonatorum in the neonate Symptoms are fever, tenderness and a scarlatiniform rash
68
What is the causative pathogen and virulence factors for Scarlet fever?
Infections with a streptococcal strain that elaborates streptococcal exotoxins or erythrogenic toxins - usually post-pharyngitis but may complicate wound infections and post-partum infections
69
Describe the signs and symptoms of Scarlet fever.
Diffuse red blush (2nd day of infection) - becomes a deeper red blanch on pressure - starts on upper chest and spreads to trunk, neck and extremities Mild eosinophilia Occlusion of sweat glands (skin feel like sandpaper) Palms, soles and face are normally spared Circum-oral pallor White strawberry tongue followed by red strawberry tongue High fever and systemic toxicity is severe cases
70
What are the major features of cutaneous anthrax?
Surrounded by extensive oedema | Painless and non-tender
71
What are the minor features of cutaneous anthrax?
Development of black eschar Progresses over 2-6 days through papular, vesicular and ulcerated stages before eschar appears - hands, forearm, face and neck are most common Discharge of serous fluid Local erythema and induration Local lymphadenopathy Systemical malaise (headache, chills and sore throat -> afebrile)
72
What are the specific risk factors for cutaneous anthrax?
Working with animals or animal hides Making, owning or playing an animal hide drum Drug use (particularly heroin) Travel Working in postal sorting office or handling large volumes of mail Received threatening letter or package containing white powder
73
What are the antibiotics used for cutaneous anthrax treatment?
``` Penicillin Flucloxacillin Clindamycin Ciprofloxacin Metronidazole ```
74
Describe PVL producing Staph aureus.
PVL is a toxin which destroys white blood cells Carried by less than 2% of S.aureus isolates (normally MSSA) Community isolates are more likely to carry the toxin that hospital
75
What conditions are associated with PVL producing S.aureus?
Necrotising fasciitis Pyogenic skin infections Septic arthritis Fulminant pneumonia
76
When should PVL producing S.aureus be suspected?
Recurrent/multiple boils | - especially those in close contact situations
77
What is the diagnosis and management plan for PVL producing S.aureus?
Screen nose, throat, axilla, perineum and skin lesions for carriage PCR for toxin gene Drainage and treatment according to sensitivity patterns Decolonise using standard MRSA regimens

Microbiology (21 decks)

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