Which symptom is indicative of a viral etiology in sinusitis compared to bacterial sinusitis?

The symptom that suggests a viral etiology in sinusitis, in comparison to bacterial sinusitis, is a duration of less than 10 days. Viral sinusitis is often self-limiting and usually presents with symptoms that resolve within this time frame. When symptoms last for a shorter duration, it typically indicates that the infection is more likely to be viral. In contrast, bacterial sinusitis often presents with a more prolonged course, frequently exceeding 10 days, on account of the nature of bacterial infections.

Facial swelling, fever, and thick nasal discharge can occur in both viral and bacterial sinusitis and are not definitive in distinguishing the etiology. Fever may be present in viral infections but can also occur in bacterial cases. Similarly, thick nasal discharge is more characteristic of bacterial sinusitis but can also appear with viral sinusitis. Therefore, the duration of symptoms is the key differentiating factor indicating a viral cause.