Differential Diagnosis for Purulent Skin Infection

Single Most Likely Diagnosis

• S. Aureus: This is the most common cause of purulent skin infections, including abscesses, furuncles, and carbuncles. Staphylococcus aureus is a gram-positive bacterium that is commonly found on the skin and can cause infection when the skin barrier is compromised.

Other Likely Diagnoses

• Group A Streptococcus: This bacterium can cause a range of skin infections, including impetigo, ecthyma, and cellulitis. While it is more commonly associated with non-purulent infections, it can also cause purulent infections, especially in certain populations.
• H. Influenzae: Although less common, Haemophilus influenzae can cause skin and soft tissue infections, including purulent infections, especially in children.

Do Not Miss Diagnoses

• Group B Streptococcus: While less common than other causes, Group B Streptococcus can cause severe infections, including necrotizing fasciitis and sepsis, especially in neonates and immunocompromised individuals. It is essential to consider this diagnosis, especially in high-risk populations.
• MRSA (Methicillin-resistant S. Aureus): This is a type of S. Aureus that is resistant to methicillin and other beta-lactam antibiotics. MRSA can cause severe and difficult-to-treat infections, and it is essential to consider this diagnosis, especially in patients with a history of MRSA colonization or infection.

Rare Diagnoses

• Other gram-negative bacteria: Such as Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae, can cause purulent skin infections, especially in immunocompromised individuals or those with underlying medical conditions.
• Anaerobic bacteria: Such as Bacteroides and Clostridium, can cause purulent skin infections, especially in the presence of devitalized tissue or foreign bodies.