Skin and Soft Tissue Infections

Question 1

What is the basis for the skin’s immunity to infection? (2)

Answer 1

• physico-chemical barriers (outer layer of skin with anti-microbial peptides)
• innate immunity (anti-microbial peptides, cytokines, dendritic cells, PMNs, complement)

Question 2

T/F: Most Skin and Soft tissue infections present sub acutely or chronically.

Answer 2

False! Most present acutely!

-red, hot, swollen, and painful

Question 3

what are the 4 characteristics of acute inflammation?

Answer 3

-red, hot, swollen, and painful

Question 4

If there is chronic inflammation in a skin/ soft tissue infection, what does it suggest? (2 things)

Answer 4

• hematogenous route of infection

- intracellular organisms

Question 5

Which 2 organisms cause most skin/soft tissue infection (SSTIs)?

Answer 5

S. Aureus

Strep pyogenes (group A strep)

Question 6

Positive gram stain color

Answer 6

purple

Question 7

negative gram stain color

Answer 7

pink

Question 8

What are the common risk factors for skin/soft tissue infections( SSTI’s)?

Answer 8

• new born infants (1-2mo)
• diabetics
• elderly
• hospitalized pt’s
• immune-compromised patients

** Note: in these patients, the differential diagnosis for the pathogen is broader, since weaker organisms can also infect them.** (mostly gram negative infections happen in these groups)

Question 9

Which test differentiates streptococci from staphylococci?

Answer 9

catalase

Question 10

Gram negative rod. Oxidase +

Answer 10

pseudomonas

Question 11

Gram negative cocci. Oxidase +

Answer 11

Neisseria meningitidis

Question 12

T/F: Most gram negative organisms are oxidase +.

Answer 12

false. most are oxidase negative

Question 13

When do fungal SSTIs occur?

Answer 13

in pt’s on broad spectrum antibiotics and/or immune-compromised states.

Question 14

How much does a break in the skin affect the ID50 of infection?

Answer 14

it lowers the ID50 (the number of organisms required for an infection in 50% of people) by over 100x!

Question 15

What are the indications for using antibiotics for a skin/soft tissue infection?

Answer 15

-systemic manifestations of the infection (abnormal vital signs)
If other risk factors for infection are present.
-diabetes
-immunosuppression
-elderly pt

Question 16

What do you do if someone has co-morbid condition (ie diabetes) and a skin/soft tissue infection?

Answer 16

• admit them tot eh hospital
• stabilize
• broad spectrum antibiotic coverage (eg, vancomycin and 3rd gen cephalosporin for gram neg’s)

Question 17

Skin infection with pus but no systemic signs of disease. Management?

Answer 17

Incise and drain only

Question 18

Infection with pus with some systemic signs of disease. Management?

Answer 18

Incise and drain, empirically treat with bactrim while waiting for culture results.

Question 19

Skin infection without pus and no pus. Management?

Answer 19

-oral penicillin, cephalosporin or clindamycin

Question 20

how does toxic shock syndrome present?

Answer 20

a diffuse erythematous rash, sharply demarcated (toxin-mediated rash pattern).

*Note: Scalded skin presents with a similar rash: diffuse erythematous, sharply demarcated, except also desquamation of the skin).

Question 21

What is the antibiotic of choice for Group A strep?

Answer 21

penicillin

Question 22

scarlet fever is caused by ?

Answer 22

group A strep - strep pyogenes.

Question 23

When should Strep Pyogenes (Group A strep) be suspected in a skin / soft tissue infection?

Answer 23

in patients with:

• lymphedema
• disrupted lymphatics
• *Case: man with Coronary Artery Bypass Graft - they use the saphenous vein for the surgery which disrupts the lymphatics - this is a warning sign for S. Pyogenes!