Podcast
Questions and Answers
What characterizes a carbuncle?
What characterizes a carbuncle?
When is imaging typically indicated for carbuncles?
When is imaging typically indicated for carbuncles?
Which imaging technique can be used to guide needle aspiration for culture in cases of a furuncle?
Which imaging technique can be used to guide needle aspiration for culture in cases of a furuncle?
What is a potential reason for performing radiographic imaging in cases of skin infection?
What is a potential reason for performing radiographic imaging in cases of skin infection?
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In what situation might a carbuncle be associated with osteomyelitis?
In what situation might a carbuncle be associated with osteomyelitis?
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What is the initial approach to diagnosing typical cases of impetigo and ecthyma?
What is the initial approach to diagnosing typical cases of impetigo and ecthyma?
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Why is bacterial culture and sensitivity testing important for patients with extensive furuncles, carbuncles, or abscesses?
Why is bacterial culture and sensitivity testing important for patients with extensive furuncles, carbuncles, or abscesses?
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In the diagnosis of large furuncles, carbuncles, and abscesses, what procedure is strongly recommended after incision and drainage?
In the diagnosis of large furuncles, carbuncles, and abscesses, what procedure is strongly recommended after incision and drainage?
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What characteristic would Gram stain reveal for S.aureus in a typical case?
What characteristic would Gram stain reveal for S.aureus in a typical case?
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Which group of infections is commonly associated with CA-MRSA strains?
Which group of infections is commonly associated with CA-MRSA strains?
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In what scenario would skin biopsies be considered for patients with furuncles or carbuncles?
In what scenario would skin biopsies be considered for patients with furuncles or carbuncles?
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What clinical signs indicate the need for more aggressive parenteral antibiotic therapy in patients with extensive infections?
What clinical signs indicate the need for more aggressive parenteral antibiotic therapy in patients with extensive infections?
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What histologic finding is typical in a furuncle?
What histologic finding is typical in a furuncle?
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Study Notes
Laboratory Testing
- Diagnosis of impetigo and ecthyma is often based on clinical presentation.
- Gram staining and culturing of pus or exudates are recommended to identify the causative organisms, typically Staphylococcus aureus (including MRSA) and/or Group A Streptococcus (GAS).
- Empiric therapy can be initiated for uncomplicated impetigo or ecthyma without performing these tests.
- Diagnosis of large furuncles, carbuncles, and abscesses is also made clinically.
- Culturing of pus obtained after incision and drainage or from open draining lesions is strongly encouraged.
- Gram staining typically reveals Gram-positive cocci in clusters (S. aureus) or chains (GAS), or a combination of both when both organisms are involved.
- Bacterial culture and sensitivity testing is crucial for guiding appropriate antibiotic therapy and monitoring for potential complications from S. aureus or GAS infections.
- In patients with extensive furuncles, carbuncles, or abscesses, vital signs and blood counts should be assessed to evaluate for systemic infection or systemic inflammatory response syndrome, as these patients may require more aggressive parental antibiotic therapy.
- Such extensive infections are frequently caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strains, which are often multidrug resistant, making antibiotic susceptibility testing essential.
- Blood cultures may be indicated if bacteremia or invasive infection is suspected.
Pathology
- Skin biopsies are generally not performed in uncomplicated cases of impetigo, ecthyma, folliculitis/furunculosis, carbuncles, or abscesses.
- Biopsy or aspiration of extensive furuncles, carbuncles, or abscesses is recommended in immunocompromised patients or those with fever and neutropenia for histological evaluation (including microorganism staining), microbiology cultures, and antibiotic sensitivity testing to aid in diagnosis and determine antibiotic susceptibility.
- Histologically, a furuncle shows a dense polymorphonuclear inflammatory process in the dermis and subcutaneous fat.
- Carbuncles present with multiple abscesses separated by connective-tissue trabeculae in the dermis (particularly along the edges of the hair follicles) reaching the skin surface through openings in the undermined epidermis.
Imaging
- Imaging is usually not indicated except for febrile neutropenic patients with extensive furuncles, carbuncles, or abscesses.
- Ultrasonography can guide needle aspiration of a furuncle, carbuncle, or abscess for culture and antibiotic susceptibility testing.
- Radiographic imaging (X-ray, CT, or MRI) can be used to determine the depth and extent of an infection, particularly when underlying osteomyelitis (e.g., in cases of S. aureus-infected foot ulcers in diabetic patients) is suspected or an indolent pulmonary site of S. aureus infection is suspected, as it can spread to the overlying skin and soft tissues.
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Description
This quiz covers the key aspects of laboratory testing for diagnosing bacterial infections such as impetigo, ecthyma, and other skin conditions. It emphasizes the importance of Gram staining, culturing techniques, and the identification of Staphylococcus aureus and Group A Streptococcus. Test your understanding of the procedures and implications of these diagnostic methods.
