Indirect causes of cellulitis (which make the eye vulnerable to a strep or staph infection) include recent surgery, bug bites, a skin wound (especially on the face) and sinusitis. Because sinusitis is more common in cold weather, cellulitis tends to occur more frequently in winter. Cellulitis can also accompany asthma, smallpox and other systemic diseases. For reasons that are not entirely clear, it appears that increased use of the flu vaccine has reduced the frequency of cellulitis, particularly pre-septal cellulitis.