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1

1. A nurse comes to your clinic with a painful finger. Examination reveals a small cluster
of pustules over the middle phalanx of her index finger. There is cellulitis surrounding the
pustules. Your best approach would be?
a) Lance and drain the pus
b) Unroof a blister and test for virus
c) Begin Cephalothin
d) Apply mupirocin ointment and elevate the hand.

B

2

2. A cat bites you. You should be concerned about getting a skin and soft tissue infection
with which group of organisms?
a) Streptococcus agalactiae, and Salmonella species
b) Pasteurella and streptococcus species
c) Capnocytophagia and clostridia
d) Pseudomonas and klebsiella

B

3

3. A frustrated football coach comes to you because several of his players have had boils
on their arms and bodies over the past three weeks. One of the players has experienced
recurrent spiderbite-like lesions over this period. The team doctor has treated them with
penicillin which seemed unhelpful. A second antibiotic course with cephalexin also proved
unsuccessful. What antibiotic would you suggest?
a) Gentamicin
b) Dicloxacillin
c) Nitrofurantoin
d) Trimethoprim-sulfa

D

4

4. A young man comes to see you in June because he has developed a “flu-like” illness
after camping and hiking on vacation in North Carolina. He’s especially concerned because
he’s developed a rash over his extremities; some spots are on his palms. The infectious cause
for this illness was probably acquired by?
a) Mosquito bite
b) Contaminated soil
c) Tick bite
d) Aerosolized white-footed mouse feces

C

5

Skin disease caused by these agents in 3 ways:

Exogenous: direct infection by agents external to the skin (ie. bacteria entering through a cut)

Endogenous: spread of organisms to the skin via the blood stream, along nerve pathways, or by extension from an adjacent site

Indirectly: from toxins produced by bacteria located outside the integument

6

EXOGENOUS INFECTIONS:
• General:

What happens in the majority of cases?
What are the most common infecting organisms?

In the majority of cases, some type of skin injury proceeds infection

Most common infecting organisms of the skin are bacterial:
o S.aureus
o S.pyogenes

7

Impetigo

Location
Typical Organism
Clinical information
Treatment

Location: Epidermis

Typical Organism: S.aureus/S.pyogenes

Clinical information:
- Weeping, crusted lesions (honey-colored)
- Patient is irritable and uncomfortable, but not febrile or seriously ill
- Post-Streptococcal Glomerulonephritis: can occur due to impetigo caused by S.pyogenes

Treatment: Topical Abx (Mupirocin)
Oral Abx

-Common among children

8

Erysipelas

Location
Typical Organism
Clinical information
Treatment

Location: Epidermis and dermis

Typical Organism: S.pyogenes

Clinical information:
-More serious
-Common in older adults
-Elevation of involved tissue, forming sharp borders
-Bright red and painful
-Fever common

Treatment: Oral or IV penicillin

9

Cellulitis

Location
Typical Organism
Clinical information
Treatment

Location: Epidermis, dermis and subcutaneous

Typical Organism: S.aureus, Streptococcus

Clinical information:
-Borders not as clear
-Fever is present
-Skin is edematous, warm, erythematous, tender and painful
-Vesicles/bullae common
-Ecchymosis in severe cases

Treatment:
Oral or IV penicillin
Cefazolin (May need to treat for CA-MRSA)

10

Folliculitis

Location
Typical Organism
Clinical information
Treatment

Location: Hair follicle (superficial)

Typical Organism: S.aureus

Clinical information:
Superficial
-Usually multifocal pustules

Treatment: --

11

Furuncle (Boil)

Location
Typical Organism
Clinical information
Treatment

Location: Hair follicle (deep)

Typical Organism: S.aureus

Clinical information:
-Deeper and more extensive
-Large, painful local boils
-Surrounding inflammation or cellulitis

Treatment:
Lance, drain (often all that is needed)
Cephalosporin/Dicloxacillin (May need to treat for CA-MRSA)

12

Carbuncle

Location
Typical Organism
Clinical information
Treatment

Location: Multiple furuncles in confined area

Typical Organism: S.aureus

Clinical information:
-Typical area is back of the neck
-Patient often acutely ill

Treatment:
-Requires systemic Abx and surgical drainage

13

Fasciitis

Location
Typical Organism
Clinical information
Treatment

Location: Fascia

Typical Organism:
S.pyogenes ("Flesh-eating strep)
S.aureus
Vibrio vulnificus (sea water exposure)
Anaerobic organisms
Polymicrobial infections including gram (-) enteric organisms

Clinical information:
-Patient acutely ill and in marked pain
-Skin overlying the infected area can be unremarkable
-Can also have changes such as gas in the tissue, hemorraghic bullae, ecchymosis, necrosis, woody induration, and cutaneous anesthesia

Treatment:
Emergency surgery and debridement
Systemic Abx (IV)

14

Myonecrosis (Gas Gangrene)

Location
Typical Organism
Clinical information
Treatment

Location: Muscle

Typical Organism:
Anaerobic streptococci
Gram (-) enterics
Clostridia spp. (gas gangrene)

Clinical information:
-Patient acutely ill and in marked pain
-Skin overlying the infected area can be unremarkable
-Can also have changes such as gas in the tissue, hemorraghic bullae, ecchymosis, necrosis, woody induration, and cutaneous anesthesia

Treatment:
Emergency surgery and debridement
Systemic Abx (IV)

15

ENDOGENOUS INFECTIONS:
• General:

- Skin can become infected by microorganisms that spread from another infected site in 3 ways
o Direct extension
o Hematogeneous Spread
o Spread along neurons

16

ENDOGENOUS INFECTIONS:

Typical Appearance:
Hematogenous Bacterial Infections:

Hematogenous Bacterial Infections: lesions are circumscribed (confined to a limited area) and appear singly or multiply as macule, papules or pustules (not spreading cellulitis)

17

ENDOGENOUS INFECTIONS:

Typical Appearance:
Hematogenous Viral Infections:

Hematogenous Viral Infections: present as widespread, symmetric lesions that frequently become confluent after initially presenting as discrete macules, papules, or vesicles (these rashes are called exanthems)

18

ENDOGENOUS INFECTIONS:

Typical Appearance:
Viral Infections with Neuronal Spread:

Viral Infections with Neuronal Spread: only local skin involvement (follow neuron)

19

Sources of Endogenous Skin Infections:
Direct Extension:

Osteomyelitis: draining sinus

Septic Arthritis: draining sinus

Lymphadenitis:
- TB
- Atypical mycobacteria
- Streptococcal infections

Oral/Dental Infection:
- Actinomycosis
- Mixed cellulitis

20

Sources of Endogenous Skin Infections
Hematogeneous Spread:

o Bacteremia
o Endocarditis
o Fungemia (candidemia)
o Viremia:
o Rocky Mountain Spotted Fever
o Secondary Syphilis: lesions on soles of the feet and palms of the hands (as well as elsewhere)

21

Endogenous Skin Infections
Hematogeneous Spread
Viremia:(4)

Measles (rubeola): exanthem (macular-papular)

Koplik spots in oral mucosa very diagnostic;

Rubella (German Measles): exanthema, macular-papular

Chicken pox: exanthem (vesicles)
- Characterized by multiple different patterns in clusters (not all spots of same type due to the fact that break-outs occur in waves and not all at once)

22

Endogenous Skin Infections
Hematogeneous Spread
Bacteremia: (4)

Menigococcus

Gonococcus: lesions spread out, usually on extremities (macules or papules)

S.aureus

Pseudomonas

23

Endogenous Skin Infections
Spread Along Neurons (2):

Herpes Simplex Infection:
- Herpes labialis: HSV-1 (vesicles on lip)
- Herpes genitalis: HSV-2 (genital vesicles/ulcers)

Varicella Zoster (Shingles): dermatomal spread in older and immunocompromised (vesicles)

24

TOXIN MEDATED SKIN DISEASE (2):

Scarlet Fever
S.aureus

25

Scarlet Fever

Causative Agent:
Description:

Causative Agent: S.pyogenes

Description: primary strep throat infection that releases an erythrogenic toxin
o Toxin spreads systematically and causes diffuse red rash that feels like sandpaper

26

Staphylococcus aureus:

• Staphylococcus aureus:

2 different toxins that cause skin disease:
o Exfoliatin
o Toxic Shock Syndrome Toxin (TSST-1)

27

Scarlet Fever

Associated Symptoms:

Circumoral pallor (white area around the mouth)

Deep red lines (Pastia’s lines) in skin fold of neck, axilla, elbows and knees

Strawberry tongue

Extensive desquamation of superficial skin layers on recovery

28

Staphylococcus aureus
Exfoliatin Toxin:

Exfoliatin: results in bullous impetigo or scalded skin syndrome (more extensive)

Bullous Impetigo: differs from the S.pyogenes impetigo due to the fact that there are large vesicles/bullae

Scalded Skin Syndrome: widespread intra-epidermal cleavage, blistering and superficial epidermal sloughing (scary, but kids often make full recovery)

29

Staphylococcus aureus
Toxic Shock Syndrome Toxin (TSST-1):

Toxic Shock Syndrome Toxin (TSST-1): Hematogenous spread of the toxin results in high fever, hypotension, multi-organ injury and diffuse erythematous rash that desquamates on recovery (especially around nail beds, hands and feet)

30

Clinical Settings and Infecting Pathogens

Hot Tub folliculitis:
Lymphatic obstruction/edema:
Aquarium exposure:
Freshwater exposure:
Salt water exposure:
Animal bites:
Fingers of healthcare workers:
Vesicles by dermatome:
Neutropenic patient:
Gangrene:

Hot Tub folliculitis: Pseudomonas

Lymphatic obstruction/edema: Streptococcus species

Aquarium exposure: Mycobacterium marinum

Freshwater exposure: Aeromonas species

Salt water exposure: Vibrio species

Animal bites: Pasteurella multocida

Fingers of healthcare workers: Herpes simplex (Whitlow)* (Endogenous)

Vesicles by dermatome: Herpes zoster* (Endogenous)

Neutropenic patient: Pseudomonas (ecthyma gangrenosum)* (Endogenous)

Gangrene: Clostridia species