ICL 1.5: Skin & Soft Tissue Infections

Question 1

what is cellulitis? what causes it?

Answer 1

an infection of the dermis and subcutaneous tissues

usually caused by streptococci (group A*, B, C, G etc) or Staphylococcus aureus

gram negatives can play a role in patients with preexistent conditions

acute!! there’s no chronic cellulitis

Question 2

how do you diagnose cellulitis?

Answer 2

diagnosis is clinical; there is no blood test or x-ray that you can take to do it

1. redness
2. heat
3. pain
4. swelling

Question 3

why is it important to differentiate between cellulitis and other stuff?

Answer 3

because when you treat people with antibiotics because you think they have cellulitis, you can give them c. diff or line infections or other problems

Question 4

what is the pathology of cellulitis?

Answer 4

the stratum corneum acts as a barrier, which is normally dry, tough, of low pH – “bricks and cement”

but breaks in this barrier may lead to pathogen invasion of deeper tissues and lead to cellulitis

Question 5

what are the risk factors for cellulitis?

Answer 5

1. any reason for skin barrier disruption (abrasion, penetrating wound, insect bite, venous ulcer, injection drug use) – not always evident!
2. edema secondary to heart failure or lymphedema secondary to mechanical blockage (damage to lymphatic veins)
3. lower extremities with stripped veins for coronary artery bypass graft (CABG) because they don’t have as good venous return to clear stuff out of the body
4. immunosuppression
5. fungal skin infection and vesicular viral rashes (varicella, zoster)
6. diabetes-induced neuropathy -> decreased sensation > ulcers > poor healing > bacteria can enter

Question 6

what is onychomycosis?

Answer 6

gross looking toe nails

it’s a risk factor for cellulitis

Question 7

what is stasis dermatitis?

Answer 7

it’s a risk factor for cellulitis due to chronic venous insufficiency

1. decreased sensation
2. red/violaceous/yellow skin changes
3. areas of chronic inflammation and areas of fibrosis
4. loss of hair
5. edema
6. cool skin, not warm as in cellulitis and it’ll be bilateral
7. chronic; not acute

many times confused with cellulitis; it is a risk factor, but not an infection

Question 8

where are the bacteria coming from that cause cellulitis?

Answer 8

it comes from the patients themselves!

1. S. aureus is carried in the anterior nares by 20-40% of adults at any given time, even higher rates in the inguinal area and in axillae
2. Group A Streptococci are carried in the nasopharynx by 15-20% of children (much lower in adults)

Question 9

what are the virulence factors that can cause cellulitis?

Answer 9

strep tends to be more rapidly invasive than staph which will form abscesses

staphylococci produce a dermonecrotic, hemolytic toxin (alpha toxin) and potent leukocidins, which kill neutrophils.

streptococci have M proteins, which enable them to escape phagocytosis and a hyaluronidase, which may allow them to spread rapidly in the tissues

Question 10

what is paronychia?

Answer 10

a collection of pus around the fingernail on the dorsal

you just treat it by opening it up and draining it (might need antibiotics)

staph can cause this or other gram negatives

Question 11

what is a felon?

Answer 11

it’s an infection in the pulp of the finger and is more aggressive than paronychia

caused by the same bacteria as paronychia

you can see this in people who chew their fingernails

Question 12

what is impetigo?

Answer 12

very superficial infection caused by staph or strep

usually in kids

honey colored crusts

you can just do local care; soap and water can help but topical or oral antibiotics will help more

Question 13

what is erysipelas?

Answer 13

superficial infection of the skin caused by group A strep

the rash has well defined borders that are raised

usually you see it on the face but can have it on the lower extremities too

it kind of looks like cellulitis

Question 14

what is folliculitis?

Answer 14

it’s infection of the oil gland accompanying the hair follicle

aka a pimple at the hairs

usually caused by staph (or pseudomonas) but will go away with soap and water

Question 15

what is a furuncle/carbuncle ?

Answer 15

bigger collection of pus but not quite an abccess yet

starts at the base of a hair follicle and it is caused by steph

more than one lesion connected by tunnels under the skin surface is a carbuncle

Question 16

what hidradenitis?

Answer 16

changes in the sweat glands that lead to a collection of stuff that looks like pus but isn’t

NOT treated with antibiotics

so you’ll see them in the armpits and butt

Question 17

what is an abccess? what causes is?

Answer 17

staph aureus 75% of the time

it’s hot, tender, white area in the middle, and you can feel like the fluid inside; it’s not just a hard mass

they may drain spontaneously but usually requires incision and drainage – antibiotics don’t really help

send a culture!!!! so you can figure out which staph it is

Question 18

how do you treat cellulitis?

Answer 18

think strep

1st generation cephalosporin

if you have periorbital/perirectal or skin necrosis along with cellulitis add a gram negative and anaerobic coverage antibiotics

Question 19

how do you treat an abscess?

Answer 19

think staph

1st generation cephalosporin even if someone is allergic to penicillin

Question 20

what are the two types of periorbital cellulitis?

Answer 20

cellulitis around the eyes

1. preseptal/periorbital = outside-in

frequent, lower mortality, caused by staph or group A strep – treat with antibiotics

2. postseptal/orbital = inside-out

rare, higher morbidity, caused by pneumococcus or fungi in diabetics

you can lose your vision from this

treat with antibiotics +/- surgical drainage

Question 21

what are the complications of orbital cellulitis?

Answer 21

septic cavernous sinus thrombosis

abrupt onset with diplopia, photophobia, orbital edema, and progressive exophthalmos

can be secondary to sinusitis, tooth infection, facial furuncles

rare, but high mortality

you have to treat it with surgical decompression of the source and antimicrobials (broad spectrum)

Question 22

what is necrotizing fasciitis?

Answer 22

involves usually superficial fascia

not common; you see it in immunocompromised or obese patients but it’s very serious and can spread reallllyyyy fast through the tissue

may be secondary to minor trauma, surgery or starting as a furuncle

you might feel crepidis = gas in the tissue

pain out of proportion when you touch the skin or the opposite; they can’t feel when you touch them

Question 23

what are the 3 types of necrotizing fasciitis?

Answer 23

1. type I = mixed flora, anaerobes + strep (non group A) + gram negatives (enterobacteriaceae, rarely pseudomonas)
2. type II = Group A strep
3. type III = clostridium perfringens (gas gangrene or clostridial myonecrosis)

Question 24

what is Fournier’s gangrene?

Answer 24

necrotizing fasciitis in the genital area

Question 25

how do you treat necrotizing fasciitis?

Answer 25

patients can be really sick because it can lead to bacteremia, sepsis, uremia, or multi organ failure

so you need to do urgent removal of dead tissue that’s filled with the toxins

you can do broadband antibiotics to cover both anaerobes and aerobes

Question 26

which bacteria is often isolated from bite infections from animals?

Answer 26

1. staphylococcus aureus
2. eikenella corrodens (humans)
3. anaerobes – Bacteroides, Prevotella, Porphyromonas
4. pasteurella multocida (dogs, cats)
5. capnocytophaga canimorsus (dogs)
6. staphylococcus intermedius

more likely to get an infection from a cat scratch

Question 27

what is pasteurella multocida? how do you treat it?

Answer 27

rapid swelling of a bite/scratch site

can cause arthritis, septicemia, endocarditis

DOC: amoxycillin or ampicillin/sulbactam

Question 28

someone says fresh or brackish water exposure or leeches what should you think of?

Answer 28

aeromonas

Question 29

someone say salt water exposure what should you think of?

Answer 29

vibrio vulnificus

can cause sepsis especially with people with liver disease

Question 30

someone say fish tanks/turtles exposure what should you think of?

Answer 30

mycobacterium marinum

Question 31

someone say meat/fish exposure what should you think of?

Answer 31

erysipelothrix rhusopathiae

Question 32

someone say gardening/roses exposure what should you think of?

Answer 32

sporothrix schenckii

Question 33

what is toxic shock syndrome?

Answer 33

usually related to S. aureus but group A streptococci can cause it too

it’s caused by a super antigen called toxic shock syndrome toxin 1 or enterotoxin

TSTT-1 binds non-specifically and activates many clones of T cells (up to 20% of all T cells) and HUGE amounts of cytokines are released into the bloodstream = disproportionate response of the immune system

this can lead to capillary leak, vasodilatation, hypotension in spite of high cardiac output, multi organ failure

diagnosis is clinical; no specific test

Question 34

what can after after someone has toxic shock syndrome?

Answer 34

peeling of skin

Question 35

what gene regulates the production of TSTT-1?

Answer 35

agr

20% of staph aureus isolates carry the gene for TSST-1 but unless they’re under the 4 required conditions, they won’t produce the toxin

Question 36

what’s the difference between TSS caused by staph vs. strep

Answer 36

staph is more common but strep is more serious

Question 37

what is scalded skin syndrome?

Answer 37

caused by staph - caused by toxins A and B

usually seen in children

Question 38

what is scarlet fever?

Answer 38

usually follows strep pharyngitis infection and is toxin-mediated

“sand paper skin”