A 15-year-old presents with 6 days of nasal congestion with thin, clear rhinorrhea.

This patient shows symptoms of acute sinusitis. The most common etiology of which is viruses. Indications that an infection is viral as opposed to bacterial included a shorter infection tie (less than 10 days) and no purulent discharge (hers is watery). She does not show any evidence of a complication developing and even notes that her symptoms are improving. If her symptoms were attributed to a bacterium, then the most common cause of acute sinusitis is Streptococcus pneumoniae followed by Haemophilus influenza, then Moraxella catarrhalis. Anaerobic species such as Bacteroides fragilis and Staphylococcus aureus are more commonly found in patients with chronic sinusitis (sinusitis lasting longer than 12 weeks). This is important to realize before indiscriminately providing antibiotics for these patients.