Differential Diagnosis for Skin Infection with Pus Drainage

• Single Most Likely Diagnosis
  • Staphylococcus aureus: This bacterium is a common cause of skin infections, including those characterized by pus drainage. It is known for causing conditions such as abscesses, folliculitis, and impetigo, which often present with purulent discharge.
• Other Likely Diagnoses
  • Streptococcus pyogenes: This bacterium can cause a range of skin infections, including impetigo and cellulitis, which may have pus drainage, especially in more severe cases.
  • Escherichia coli or other Gram-negative bacteria: While less common than S. aureus for skin infections, these bacteria can cause infections, particularly in the context of compromised skin integrity or in immunocompromised patients.
  • Pseudomonas aeruginosa: This bacterium can cause skin infections, especially in the setting of compromised skin barriers (e.g., burns, wounds) and can produce a blue-green pus due to its pigments.
• Do Not Miss Diagnoses
  • Methicillin-resistant Staphylococcus aureus (MRSA): Although MRSA infections can present similarly to those caused by methicillin-susceptible S. aureus, the antibiotic resistance pattern of MRSA makes it crucial to identify to ensure appropriate treatment.
  • Gas gangrene (Clostridium perfringens): This is a severe, potentially life-threatening condition characterized by necrotic infection of soft tissue, which can produce gas and pus. Early recognition is critical for effective management.
• Rare Diagnoses
  • Actinomyces israelii: This bacterium can cause actinomycosis, a chronic infection that can involve the skin and produce pus, but it is much less common than other bacterial causes.
  • Nocardia species: These bacteria can cause nocardiosis, which may present as a skin infection with pus drainage, particularly in immunocompromised individuals.
  • Cutaneous tuberculosis: Although rare in many parts of the world, cutaneous tuberculosis can cause skin lesions that may drain pus, and it is essential to consider in patients with risk factors for tuberculosis.