Skin and soft tissue infections

1. Skin and Soft Tissue Infections
Saahir Khan, Jennifer Mah, Stephanie
Singson, Cory Taylor, Sam Lai
UCI Internal Medicine Residency
December 19, 2014

2. Pathogenesis

3. Necrotizing Fascitis Contact Dermatitis Cellulitis
Erysipelas Erythema Multiforme Ecthyma
Deep Vein Thrombosis Folliculitis Impetigo

4. • Impetigo
– Non-Bullous: GAS, MSSA, rarely MRSA
– Bullous: MSSA with exfoliative toxin, rarely MRSA, purulent
– If localized, topical treatment x 5 days unless risk for MRSA
– If widespread, oral treatment against MSSA x 7 days unless risk for MRSA
– Staphylococcal Scalded Skin Syndrome: IV nafcillin + clindamycin for toxin
• Ecthyma
– GAS, MSSA, rarely MRSA, use oral treatment against MSSA x 7 days unless risk for MRSA
– Ecthyma Gangenosum: immunocomprise or trauma, Pseudomonas, systemically ill
• Folliculitis
– MSSA, MRSA, rarely Pseudomonas (hot tub), Aeromonas (lake), fungal
– Use warm compress or topical treatment
• Furuncule/Carbuncle/Abscess
– MSSA, MRSA, purulent
– Treat with incision and drainage
– Adjunctive oral treatment against MSSA if SIRS or incomplete drainage
– Empiric treatment against MRSA if colonized, septic, immunocompromised, failed
treatment, or high MRSA prevalence
– If recurrent in same location, look for anatomic cause, consider decolonization
– If multiple locations, look for immunodeficiency, consider decolonization
Stevens, DL, Bisno, AL, Chambers, HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update
by the Infectious Diseases Society of America. Clin Infect Dis. 2014.
superficial
deep

5. • Erysipelas, Cellulitis
– GAS, MSSA, MRSA
– Culture blood if immunocompromised, animal bite, exposure
– Use oral treatment against MSSA if uncomplicated
– Use systemic treatment if SIRS
– Use treatment against MRSA if trauma, colonization, septic
– Use broad treatment including gram-negatives if immunocompromised
– Hospitalize if SIRS, immunocompromised, poor adherence, failed treatment, or concern
for deep infection
– Treat after 4 days post-op if SIRS and wound inflammation with site-dependent regimen
– Treat for 5 days, then extend until symptoms resolve
– For recurrence, address underlying anatomic causes, consider prophylaxis if 4/year
• Necrotizing Fascitis
– Type 1 = Mixed anaerobic and facultative (strep, gram-negatives), Type 2 = GAS
– Clostridial Myonecrosis: C. perfringens, gas-producing
– Prompt surgical consultation if suspected
– Workup with MRI if able to be performed quickly or CT and culture of blood and abscess
– Use broad IV treatment including anaerobes, add clindamycin for toxin if suspecting GAS
– Treat within 2-4 days post-op if SIRS and wound purulence with GAS or Clostridium
– If persistently bacteremic, look for residual or metastatic abscess or endocarditis
– Treat for 3 weeks, can use oral abx if blood clear, no endocarditis, no abscess
superficial
deep
Stevens, DL, Bisno, AL, Chambers, HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update
by the Infectious Diseases Society of America. Clin Infect Dis. 2014.

6. Stevens, DL, Bisno, AL, Chambers, HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update
by the Infectious Diseases Society of America. Clin Infect Dis. 2014.
Moderate:
SIRS
Severe:
septic, failed treatment,
immunocompromised,
deep involvement

7. Swartz, MN. Cellulitis. N Engl J Med. 2004; 350:904-12.

8. Stevens, DL, Bisno, AL, Chambers, HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update
by the Infectious Diseases Society of America. Clin Infect Dis. 2014.
Empiric Treatment against GAS/MSSA

9. Daum, RS. Skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus. N Engl J Med. 2007; 357:380-90.
Empiric Oral Treatment against MRSA

10. 1. A 24 year old male is evaluated for an increasingly painful boil on his back
that has been present for 3 days and has increased in size. The patient has
had similar lesions on his back and chest previously, but these were smaller
and spontaneously drained and resolved with requiring medical attention.
The remainder of the medical history is non contributory. On physical exam,
vital signs are normal and the patient is not all appearing. Examination of the
back discloses a 7cm fluctuant, tender, oval shaped lesion, with surrounding
erythema extending 3cm from the edge of lesion. The remainder of the
physical exam is normal.
An aspirate of the lesion reveals purulent material, a Gram stain of which
demonstrates many leukocytes and many gram positive cocci in clusters. A
culture is sent for procession. Incision and drainage of the lesion produces
approximately 5ml of pus.
Which of the following is the most appropriate antibiotic treatment for this
patient?
A. Amoxicillin- Clavulanate
B. Azithromycin
C. Moxifloxacin
D. Rifampin
E. Trimpethoprim-Sulfamethoxazole

11. Answer: E. TMP-SMX is an older antibiotic that has been used with increasing
frequency for treatment of skin and soft tissue infections caused my
community associated MRSA and it has retained excellent activity against
most trains of CA-MRSA. This patient presents with a cutaneous abscess that
is larger than 5cm with purulent drainage and associated cellulitis. A gram
stain of the lesion aspirate is suggestive of S. aureus which is consistent with
CA-MRSA infection. Treatment with TMP-SMX is appropriate empiric therapy
after drainage of the lesion. Limitations of TMP-SMX include sulfa allergy,
hyperkalemia, and possible kidney toxicity.
Amoxicillin-Clavulanate is an expanded spectrum beta lactam that is not
active against MRSA. Azithromycin, a macrolide,has poor activity against
MRSA. Moxifloxacin, a fluoroquinolne, has increased activity against S. aureus
compared with other fluoroquinolones but resistance to this agent has
emerged among CA-MRSA strains. Rifampin has activity against some CA-
MRSA strains but should not be used as a single agent for treatment of
infection because of the risk of rapid emergence of resistance.
Key Point: Trimethoprim-Sulfamethoxazole is a first line choice for treatment
of skin and soft tissue infection due to suspected or confirmed community
associated MRSA.

12. 2. A 25 year old woman is evaluated for redness that developed over her right
leg at the site of a mosquito bite. She is otherwise healthy and takes no
medications. On physical exam, temperature is 37.2C, BP 120/70, HR 70/min,
RR 14/min. There is an erythematous 3x3-cm patch on the right thigh. The
area is warm to touch with no evidence of purulence, fluctuance, crepitus or
lymphadenopathy.
Which of the following is the most appropriate empiric outpatient therapy?
A. Cephalexin
B. Doxycline
C. Fluconazole
D. Metronidazole
E. Trimethoprim-Sulfamethoxazole

13. Answer: A. The patient has non purulent cellulitis that is most likely caused
by group A B-hemolytic streptococci and empiric treatment with a B-lactam
agent such as Cephalexin or Dicloxacillin is recommended. Cellulitis is a
bacterial skin infection involving the dermis and subcutaneous tissues. This
infection is most frequently associated with dermatologic conditions involving
breaks in the skin, such as eczema, tinea pedis or chronic skin ulcers, and
conditions leading to chronic lymphedema. Cellulitis should be suspected in
patients with the acute onset of spreading erythema, edema, pain or
tenderness and warm. Fever, although uncommon, is not uniformly present.
Doxycycline and TMP-SMX have activity against CA-MRSA but are not reliably
effective against B-hemolytic streptococci.

14. 3. A 20 year old man is evaluated for a scratch on his right arm from a pet
kitten that occurred 3 weeks ago. The patient now has a skin lesion at the
inoculation site and painful swelling in the ipsilateral axillary area. He is also
experiencing malaise. Medical history is unremarkable.
On physical exam, temperature is 37.2C, blood pressure 120/80, HR 80/min
and RR 14/min. A red papule is present on the biceps of the right arm and
tender right axillary lymphadenopathy with overlying erythema is noted. The
remainder of the exam is normal.
Lab studies indicate a leukocyte count of 11,500/uL with 83% neutrophils and
17% lymphocytes and a normal metabolic panel.
Which of the following is the most appropriate treatment?
A. Azithromycin
B. Dicloxacillin
C. Itraconazole
D. Linezolid

15. Answer: A. The patient has cat scratch disease and treatment with
Azithromcyin is recommended. Cat scratch disease often occurs in
immunocompetent children and young adults and is caused by inoculation of
the fastidious gram negative bacterium Bartonella henselae after the scratch
of a kitten or cat. A pustule or papule or erythema develops at the site of the
inoculation several days to 2 weeks after the injury. Significant tender
regional lymphadenopathy develops 2-3 weeks after inoculation in areas that
drain the infected site. These lymph nodes suppurate in a small number of
patients. Lymphadenopathy generally resolves within months and extranodal
disease is rare.
Although cat scratch disease is usually a self-limited illness, some exports
recommend a short course of treatment with azithromycin. Other agents that
can be used include doxycycline, rifampin, clarithromycin, TMP-SMX and
ciprofloxacin.
Linezolid and dicloxacillin are used primarily to treat gram positive bacteria
such as staphylococci and streptococci and are not effective against gram
negative organisms such as B. henselae.

16. 4. A 63-year-old woman is evaluated for fever and hypotension for four days after kidney-
pancreas transplantation surgery. She was treated with cyclosporine prednisolone and
mycophenolate mofetil. The incisional pain has not increased and except for slightly increased
erythema surrounding the incision there are no localizing signs or symptoms. Medical history
significant for type one diabetes since age of 12 years. It's at the onset of her current symptoms
she has been doing well after surgery.
On physical examination temperature is 39.4°C blood pressure is 80/52 pulse rate is 100 per
minute and respiration rate is 20 per minute. Cardiopulmonary examination is normal. On the
abdominal examination there is erythema surrounding the surgical right lower quadrant incision
and moderate tenderness to palpation of the surgical wound. The remainder of the examination
is normal.
Laboratory studies show hemoglobin 12.1 g/dL. Leukocyte count 13,400. Creatinine 1.9.
Urinalysis with 7 leukocytes, 25 erythrocytes and trace protein. The patient and organ donor are
serologically positive for cytomegalovirus infection.
Chest radiographic shows no infiltrates. Abdominal radiographs show only a small amount of free
peritoneal gas. CT scans of the chest and abdomen revealed only some peri-incisional fluid.
Which of the following is the most likely cause of this patient's current symptoms and findings?
A. Candidal wound infection
B. Cytomegalovirus infection
C. Pneumocystis pneumonia
D. Staphylococcal wound infection

17. Answer: D. This patient's symptoms are most likely attributable to a postoperative wound
infection considering the recent surgery, rapid onset of high fever, leukocytosis, wound erythema
and tenderness, presence of peri- incisional fluid, and lack of signs and symptoms supporting
other likely problems in the immediate postoperative period.
In patients receiving solid organ transplants, infections in the immediate postoperative period are
similar to those occurring in patients who have undergone other types of surgery. Post
transplantation wound infections from staphylococci (coagulase negative and Staphylococcus
aureus), hemolytic streptococci, or enteric bacteria occur commonly.
Candidal wound infection would be less likely than staphylococcal wound infection in this patient
because of the acuity of onset, leukocytosis, and high fever. Candidal infections are very
uncommon and would be expected to be more chronic in nature.
Cytomegalovirus infection is unlikely because it would rarely become clinically apparent this soon
after surgery and with such a short duration of immunosuppressive therapy. Because the donor
and recipient are both serologically positive for CMV, CMV infection would occur between the
second and sixth months after surgery unless prophylaxis is given.
Pneumocystis pneumonia is unlikely to be responsible for this patient's current signs and
symptoms because it is not likely to occur this soon after transplantation, and this patient
demonstrates no respiratory signs and symptoms and has a normal pulmonary examination and
chest x-ray.
Key Point: infections in the immediate post-transplantation period are usually the same as those
occurring after other kinds of surgery and include staphylococci (coagulase negative and
Staphylococcus aureus), hemolytic streptococci, or enteric bacterial wound infection.

18. 5. A 60 year old woman who presents with a rash on both of her legs that has
been present for two months. She reports no pain but does experience mild
pruritus. Her past medical history significant for obesity, hypertension, and
diabetes with her last hemoglobin A-1 C at 6.7. She takes lisinopril,
metoprolol, and glyburide. She has no known drug allergies. On physical exam
her temperature was 38°C, blood pressure 130/80, heart rate 82, respiratory
rate 14. She has large erythematous plaques with fine fissuring and scaling as
well as interspersed brown macular hyperpigmentation. She has trace edema
up to her mid shins. There is no purulent drainage. The rest of her exam is
normal.
What is her most likely diagnosis?
A. Atopic dermatitis
B. Bilateral cellulitis
C. Stasis dermatitis
D. Tinea corporis

19. Answer: C. Stasis dermatitis typically presents with erythema, scaling,
pruritus, erosions, exudate, and crusting. Usually located in the lower third of
the legs, superior to the medial malleolus. Can occur bilaterally or unilaterally.
Edema is often present, as well as varicose veins and hemosiderin deposits.
Adults with atopic dermatitis have a history of childhood atopic dermatitis
and a different distribution of skin involvement.
Cellulitis typically occurs more acutely. Sometimes presents with fever and
pain. Examination reveals more erythema with lymphangitic streaking and no
scaling.
With tinea corporis, you would see sharply marginated, erythematous
annular patches with central clearing.

20. Amin, AN, Cerceo, EA, Deitelzweig, SB, et al. Hospitalist perspective on the treatment of skin and soft
tissue infections. Mayo Clin Proc. 2014; 89(10):1436-1451.
→ Even though this article has more of an inpatient focus, it is a good review of the common
pathogens and treatment options.
Daum, RS. Skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus. N Engl
J Med. 2007; 357:380-90.
→ MRSA skin infections are commonly necrotic.
→ Oral antibiotic options include clindamycin, Bactrim, doxycycline, minocycline, linezolid, and
rifampin. Bactrim and tetracyclines are not recommended as sole empiric therapy for nonpurulent
cellulitis.
→ Inpatient therapies include vancomycin, clindamycin, daptomycin, tigecycline, linezolid, and
quinupristin.
Gunderson, CG, Chang, JJ. Risk of deep venous thrombosis in patients with cellulitis and erysipelas: a
systematic review and meta-analysis. Thrombosis Research. 2013; 132:336-40.
→ While DVT is often considered in the differential for cellulitis and erysipelas, patients with cellulitis
are not at increased risk for DVT.
Stevens, DL, Bisno, AL, Chambers, HF, et al. Practice guidelines for the diagnosis and management of
skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect
Dis. 2014.
Swartz, MN. Cellulitis. N Engl J Med. 2004; 350:904-12.
→ Cellulitis involves the dermis and subcutaneous tissue, and lacks sharp demarcation .
→ Erysipelas is a superficial cellulitis that involves lymphatics. It is indurated with a raised border that is
demarcated from normal skin.