Skin infections Flashcards
What are the pathogens responsible for honey crusted lesions?
- S aureus
- S pyogenes
What are the key clinical features of erysipelas?
- Fever and rapid onset.
- Well-demarcated
- Bright red
- Raised plaques
- Often involves the face or legs
What is the most common cause of erysipelas?
Streptococcus pyogenes (Group A Streptococcus)
A 45-year-old female presents to your office with fever, malaise and facial rash. The symptoms started acutely one day ago, and she took two tablets of ibuprofen to relieve the fever. Her past medical history is insignificant. She works as a clerk at a private office, and is not physically active. She smokes two packs of cigarettes daily, and consumes alcohol occasionally. She denies any recreational drug use. She has no known allergies. She is sexually active in a monogamous relationship with her husband. The rash is shown. Other physical findings are within normal limits. What is the most likely cause of this patient’s problem?
The clinical scenario described is highly suggestive of erysipelas, a specific form of cellulitis. Currently, the lower extremities are the most common sites of involvement, but the face is involved in 5 to 20% of patients. The lesion is usually characteristic: it is red, painful, edematous, and elevated. A sharp demarcation from the uninvolved skin is usually present, and a butterfly pattern involving the cheeks and the bridge of the nose may be seen. Other characteristic features of erysipelas are an abrupt onset and the presence of systemic symptoms (fever, chills, malaise, etc). Group-A streptococcus is the typical etiologic agent of erysipelas, although sometimes, other beta-hemolytic streptococci are involved.
What is the first-line treatment for erysipelas?
Oral penicillin or cephalexin (IV if severe).
Which skin infection is associated with breaks in the skin, such as insect bites or trauma?
Cellulitis
How does cellulitis present clinically?
Ill-defined, warm, tender erythema involving deep dermis and subcutaneous fat. Gradual onset.
What is the most common cause of (nonpurulent) cellulitis?
Streptococcus pyogenes (Group A Streptococcus)
How is nonpurulent cellulitis treated?
Cephalexin or dicloxacillin. If MRSA suspected, add TMP-SMX or doxycycline.
How does an abscess present clinically?
Fluctuant, tender, erythematous nodule with pus accumulation within dermis or subcutaneous tissue.
What is the most common cause of abscesses?
Staphylococcus aureus (including MRSA)
What is the best treatment for an abscess?
Incision & drainage. Add antibiotics if systemic symptoms or surrounding cellulitis present.
What is the most common cause of necrotizing fasciitis?
- Streptococcus pyogenes (most common)
- Polymicrobial infections
- Clostridium perfringens
- Vibrio vulnificus (in marine injuries)
Which soft tissue infection has the most rapid progression?
Necrotizing fasciitis
What are the hallmark signs of necrotizing fasciitis?
Severe pain out of proportion to exam, rapid progression, crepitus, skin discoloration, bullae, systemic toxicity (fever, hypotension).
What is the immediate management of necrotizing fasciitis?
Urgent surgical debridement + broad-spectrum IV antibiotics (piperacillin-tazobactam + vancomycin + clindamycin to inhibit toxin production).
What mibrobe commonly causes a skin infection after a tick bite?
Borrelia burgdorferi causes Lyme disease, which can present with erythema migrans. This classic bullseye rash is not painful and is usually accompanied by nonspecific symptoms, such as fever, malaise, and headache. In addition, erythema migrans typically develops 1-2 weeks after the bite.
What skin infection commonly is associated with wrestling or other contact sports?
Trichophyton species can cause tinea corporis, a dermatophyte infection common in athletes who participate in contact sports. The rash is pruritic with central clearing and raised borders, and is not tender or warm.
