Orbital cellulitis causes
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Orbital cellulitis occurs commonly from bacterial infection spread by the paranasal sinuses. Other ways in which orbital cellulitis may occur is from infection in the blood stream and from an eyelid skin infection. Upper respiratory infection, sinusitis, trauma to the eye, ocular or periocular infection and systemic infection all increase one’s risk of orbital cellulitis.Staphylococcus aureus, Streptococcus pneumoniae and beta-hemolytic streptococci are three bacteria that can be responsible for orbital cellulitis.
Causes
- Staphylococcus aureus, is a gram-positive bacterium which is the most common of staph infections. Staphylococcus aureus infection can spread to the orbit from the skin. Staph organisms are able to produce toxins which promote their virulence which leads to the inflammatory response seen in orbital cellulitis. Staphylococcus infections are identified by a cluster arrangement on gram stain. Staphylococcus aureus forms large yellow colonies (which is distinct from other Staph infections such as Staphylococcus epidermis which forms white colonies).
- Streptococcus pneumoniae, is also a gram-positive bacterium responsible for orbital cellulitis due to its ability to infect the sinuses (sinusitis). Strep organisms are able to determine their own virulence and can invade surrounding tissues causing an inflammatory response seen in orbital cellulitis (similar to Staphyloccoccus aureus). Streptococcal infections are identified on culture by their formation of pairs or chains. Streptococcus pneumoniae produce green (alpha) hemolysis, or partial reduction of red blood cell hemoglobin.