A 1-year-old unimmunized boy is brought to the emergency department by his mother because of fever, eyelid swelling, and erythema for the past 24 hours. On examination, the child is febrile to 39ºC and irritable. The right upper and lower eyelids are swollen and erythematous, with no proptosis (Figure 17-1). His extraocular movements are intact. A blood culture and complete blood count are drawn and the patient is admitted to the hospital for preseptal cellulitis and treated with intravenous antibiotics. Twenty-four hours later, the blood culture grows Haemophilus influenzae type b. He was treated with intravenous antibiotics and recovered completely.

Preseptal (or periorbital) cellulitis is a bacterial infection of the eyelid anterior to the orbital septum that can result from bacteremia or from direct extension from the surrounding skin. It should always be distinguished from orbital cellulitis, which involves the tissue posterior to the septum (Figure 17-2).

Periorbital cellulitis or preseptal cellulitis.

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  Preseptal cellulitis is most common in young children, occurring at a mean age of 21 months.^1,2

  
  
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  Because there are multiple modes of infection, periorbital cellulitis is more common than orbital cellulitis.^3,4

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  The source of infection and mode of transmission can predict the bacteriology of the infection.

  
  
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  The most common route of infection is from a breech in the skin overlying the eyelid or face, such as external trauma to the eye, an insect bite, or dacryocystitis (Figure 17-3).

  
  
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  Staphylococcus aureus (including community-associated methicillin-resistant S aureus [MRSA]) and Streptococcus pyogenes (Group A) are the most common pathogens when the route of infection is secondary to direct spread from the skin.³

  
  
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  Community acquired-MRSA has become an emerging pathogen causing preseptal cellulitis.⁵

  
  
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  Sinusitis can be associated with preseptal cellulitis, although orbital cellulitis is the more common complication of sinusitis. When sinusitis is the source of infection, the usually causative organisms are Streptococcus pneumoniae, H influenzae, and anaerobes.^2,4

  
  
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  Hematogenous spread (bacteremia) is another route of infection and mainly occurs in infants less than 2 years of age. In these cases, H influenzae type b (Hib), S pneumoniae, and S pyogenes are the most common pathogens.⁶

  
  
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  The incidence of bacteremic preseptal cellulitis has decreased significantly because of widespread immunization with HIB vaccine. However, HIB infection should always be considered in unimmunized children (Figure 17-1).⁴