SSTI Flashcards
FOLLICULITIS
* S. aureus is the most common cause of localized folliculitis
* Hot-tub folliculitis is caused by Pseudomonas aeruginosa in waters that are insufficiently chlorinated and maintained at temperatures of 37–40C.
* usually self-limited, although bacteremia and shock have been reported
* Swimmer’s itch occurs when a skin surface is exposed to water infested with freshwater avian schistosomes
* Free-swimming schistosomal cercariae readily penetrate human hair follicles or pores but quickly die and elicit a brisk allergic reaction, causing intense itching and erythema
ERYSIPELAS
* Erysipelas is due to S. pyogenes
* characterized by an abrupt onset of fiery-red swelling of the face or extremities
* well-defined indurated margins, particularly along the nasolabial fold
* rapid progression
* intense pain
* extension to deeper soft tissues is rare
* Treatment with penicillin is effective
* Desquamation of the involved skin occurs 5–10 days into the illness
NECROTIZING FASCIITIS
* formerly called streptococcal gangrene
* may be associated with group A Streptococcus or mixed aerobic– anaerobic bacteria or may occur as a component of gas gangrene caused by Clostridium perfringens
* Strains of MRSA that produce the Panton-Valentine leukocidin (PVL) toxin have been reported to cause necrotizing fasciitis.
- Necrotizing fasciitis caused by mixed aerobic–anaerobic bacteria begins with a breach in the integrity of a mucous membrane barrier
- Other predisposing factors include peripheral vascular disease, diabetes mellitus, surgery, and penetrating injury to the abdomen
- Leakage into the perineal area results in a syndrome called Fournier’s gangrene, characterized by massive swelling of the scrotum and penis with extension into the perineum or the abdominal wall and the legs.
- There are two distinct clinical presentations: those with no portal of entry and those with a defined portal of entry.
- Prompt surgical exploration down to the deep fascia and muscle is essential
- Necrotic tissue must be surgically removed, and Gram’s staining and culture of excised tissue
Which of the following organisms is the most common cause of localized folliculitis?
A) Pseudomonas aeruginosa
B) Staphylococcus aureus
C) Streptococcus pyogenes
D) Clostridium perfringens
Answer: B) Staphylococcus aureus
Rationale: S. aureus is the most common cause of localized folliculitis, a superficial infection of hair follicles. Hot-tub folliculitis is caused by Pseudomonas aeruginosa, not S. aureus.
Hot-tub folliculitis is caused by which of the following pathogens?
A) Staphylococcus aureus
B) Pseudomonas aeruginosa
C) Streptococcus pyogenes
D) Klebsiella pneumoniae
Answer: B) Pseudomonas aeruginosa
Rationale: Pseudomonas aeruginosa thrives in warm, inadequately chlorinated water (37–40°C), leading to hot-tub folliculitis. The condition is usually self-limited, though bacteremia and shock can occur in rare cases.
Which of the following conditions is caused by freshwater avian schistosomes?
A) Hot-tub folliculitis
B) Swimmer’s itch
C) Necrotizing fasciitis
D) Erysipelas
Answer: B) Swimmer’s itch
Rationale: Swimmer’s itch occurs when schistosomal cercariae penetrate human hair follicles or pores, causing intense itching and erythema due to an allergic reaction. Unlike bacterial folliculitis, this condition is due to parasitic infection.
Which of the following pathogens is responsible for erysipelas?
A) Staphylococcus aureus
B) Pseudomonas aeruginosa
C) Streptococcus pyogenes
D) Clostridium perfringens
Answer: C) Streptococcus pyogenes
Rationale: Streptococcus pyogenes is the primary cause of erysipelas, which is characterized by abrupt-onset fiery-red swelling with well-defined indurated margins and rapid progression.
The preferred treatment for erysipelas is:
A) Vancomycin
B) Amoxicillin-clavulanate
C) Penicillin
D) Fluoroquinolones
Answer: C) Penicillin
Rationale: Penicillin is the treatment of choice for erysipelas caused by S. pyogenes. The infection rarely extends into deeper soft tissues and responds well to penicillin therapy.
Which of the following best describes cellulitis?
A) A localized infection with a focal area of pus
B) A superficial infection with indurated margins
C) A rapidly spreading infection with diffuse borders
D) A chronic infection associated with fibrosis
Answer: C) A rapidly spreading infection with diffuse borders
Rationale: Cellulitis is characterized by pain, erythema, swelling, and heat and spreads rapidly, especially when caused by Streptococcus pyogenes. It is not localized, unlike abscesses or folliculitis.
Which of the following antibiotics is appropriate for treating cellulitis caused by MSSA?
A) Nafcillin
B) Vancomycin
C) Trimethoprim-sulfamethoxazole
D) Clindamycin
Answer: A) Nafcillin
Rationale: Methicillin-sensitive Staphylococcus aureus (MSSA) responds well to nafcillin or first-generation cephalosporins (e.g., cefazolin). MRSA infections require vancomycin or trimethoprim-sulfamethoxazole.
Which of the following conditions is associated with Aeromonas hydrophila infection?
A) Hot-tub folliculitis
B) Cellulitis following freshwater injury
C) Erysipelas
D) Swimmer’s itch
Answer: B) Cellulitis following freshwater injury
Rationale: Aeromonas hydrophila causes aggressive cellulitis and occasionally necrotizing fasciitis following freshwater lacerations. It is sensitive to fluoroquinolones, aminoglycosides, and third-generation cephalosporins.
A patient presents with cellulitis that developed after a dog bite. Which of the following is the most appropriate antibiotic choice?
A) Penicillin
B) Amoxicillin-clavulanate
C) Vancomycin
D) Azithromycin
Answer: B) Amoxicillin-clavulanate
Rationale: Animal or human bite infections often involve polymicrobial flora, including anaerobes. Amoxicillin-clavulanate provides broad coverage against these pathogens.
Which of the following organisms is most commonly associated with necrotizing fasciitis?
A) Streptococcus pyogenes
B) Pseudomonas aeruginosa
C) Candida albicans
D) Legionella pneumophila
Answer: A) Streptococcus pyogenes
Rationale: Necrotizing fasciitis is often caused by group A Streptococcus and mixed aerobic-anaerobic bacteria. It progresses rapidly and requires urgent surgical intervention.
Which of the following factors is a major risk for Fournier’s gangrene?
A) Hypertension
B) Peripheral vascular disease
C) Asthma
D) Hyperthyroidism
Answer: B) Peripheral vascular disease
Rationale: Fournier’s gangrene is a form of necrotizing fasciitis affecting the perineum, often associated with diabetes mellitus and peripheral vascular disease.
Which toxin is produced by MRSA strains that cause necrotizing fasciitis?
A) Exfoliative toxin A
B) Panton-Valentine leukocidin (PVL)
C) Diphtheria toxin
D) Botulinum toxin
Answer: B) Panton-Valentine leukocidin (PVL)
Rationale: PVL toxin is associated with MRSA-related necrotizing fasciitis, leading to severe soft tissue destruction.
What is the primary treatment for necrotizing fasciitis?
A) IV antibiotics alone
B) Surgical debridement and IV antibiotics
C) Hyperbaric oxygen therapy alone
D) Topical antimicrobial therapy
Answer: B) Surgical debridement and IV antibiotics
Rationale: Surgical debridement is essential to remove necrotic tissue, and IV broad-spectrum antibiotics (e.g., carbapenems, vancomycin, clindamycin) are required for treatment.
