A 10-year-old girl has had a cold for 14 days. In the 2 days prior to the visit to your office, she has developed a fever of 39°C (102.2°F), purulent nasal discharge, facial pain, and a daytime cough. Examination of the nose after topical decongestants shows pus in the middle meatus. Which of the following is the most likely diagnosis?
a) Viral pharyngitis
b) Allergic rhinitis
c) Acute bacterial sinusitis
d) Epiglottitis