How can I differentiate between a viral upper respiratory tract infection and bacterial sinusitis in a primary care setting?

In primary care, differentiating between a viral upper respiratory tract infection (URTI) and bacterial sinusitis primarily relies on clinical assessment of symptom duration, severity, and specific features. Viral URTIs typically present with symptoms such as nasal congestion, sore throat, cough, and mild fever lasting less than 10 days, often improving without antibiotics. In contrast, bacterial sinusitis is more likely when symptoms persist beyond 10 days without improvement, or worsen after an initial improvement, and may include unilateral facial pain or tenderness, purulent nasal discharge, and high fever.

According to NICE guidelines, acute respiratory infections (ARIs) including sinusitis should be assessed clinically without routine use of rapid microbiological tests, as these do not reliably distinguish viral from bacterial causes in primary care ¹. The guidelines recommend considering the overall clinical picture, including symptom duration and severity, and the presence of systemic features such as high fever or facial pain, to guide antibiotic prescribing decisions ¹.

Supporting literature aligns with this approach, emphasizing that bacterial sinusitis often follows a viral URTI and is suggested by prolonged symptoms (>10 days), severe symptoms such as intense facial pain or swelling, and purulent nasal discharge (Butler and Hernandez, 2025). Viral URTIs tend to have a more gradual onset and resolve within 7-10 days without specific treatment (Rabinowitz, 1990; Wei and Norwood, 2001).

In summary, in primary care, the key differentiators are symptom duration beyond 10 days, worsening after initial improvement, and localized signs of bacterial infection such as unilateral facial pain and purulent nasal discharge, which suggest bacterial sinusitis rather than a viral URTI. Clinical judgement remains paramount, supported by NICE recommendations to avoid unnecessary antibiotic use and to provide self-care advice unless bacterial infection is strongly suspected ¹.