Fast Five Quiz: Cellulitis Key Aspects

Michael Stuart Bronze, MD


January 23, 2020

Streptococcal species are the most common causes of erysipelas and diffuse cellulitis or nonpurulent cellulitis that is not associated with a defined portal. Staphylococcus aureus is the usual causative organism in purulent cellulitis associated with furuncles, carbuncles, or abscesses. In individuals with normal host defenses, the most common causative organisms are group A streptococci and S aureus. Group B Streptococcus cellulitis occurs in infants younger than 6 months because their immune responses are not fully developed, and it may also be seen in adults with comorbidities, such as diabetes or liver disease. For infantile cellulitis, presentations may include sepsis.

Violaceous color and bullae suggest more serious or systemic infection with such organisms as Vibrio vulnificus or Streptococcus pneumoniae. Immunocompromised hosts may become infected from nontraditional cellulitis organisms, including gram-negative rods (eg, Pseudomonas, Proteus, Serratia, Enterobacter, Citrobacter), anaerobes, and others (eg, Helicobacter cinaedi, Fusarium spp). Although fungi (eg, Cryptococcus) and herpes simplex virus may also cause cellulitis, these causes are rare.

Pneumococci may cause a particularly malignant form of cellulitis that is frequently associated with tissue necrosis, suppuration, and bloodstream invasion. Mycobacterial infections may present as cellulitis.

Read more about risk factors for cellulitis.


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