What are the key clinical features that differentiate bacterial conjunctivitis from viral or allergic conjunctivitis in primary care?

Differentiating between bacterial, viral, and allergic conjunctivitis in primary care involves assessing key clinical features, including the nature of discharge, presence of itching, and associated systemic symptoms ¹,².

• Bacterial Conjunctivitis: This type of conjunctivitis often presents with a purulent discharge, which can be significant enough to cause encrusted eyelids ¹,³. Most cases are self-limiting and resolve within 5–7 days, though topical antibiotics can be considered for severe cases or if rapid resolution is required ¹.
• Viral Conjunctivitis: Viral conjunctivitis is typically self-limiting and usually resolves within one to two weeks without antimicrobial treatment ¹. Discharge may be present, which can be managed by bathing and cleaning the eyelids ¹. A key differentiating factor is that topical antibiotics are not appropriate for viral conjunctivitis and may cause adverse reactions ¹. Viral conjunctivitis is also highly contagious, and patients should be advised on measures to prevent spread ¹.
• Allergic Conjunctivitis: A prominent feature of allergic conjunctivitis is prolonged severe itching ². It may also be associated with other systemic allergic symptoms, such as nasal and respiratory symptoms ². Management focuses on allergen identification and avoidance, and specialist referral may be considered for multisystem disease or persistent symptoms ².

While bacterial and viral conjunctivitis are infective, viral conjunctivitis is specifically highlighted as contagious, requiring measures to prevent spread ¹. The presence of significant itching strongly points towards an allergic cause ². The type of discharge (purulent for bacterial versus less specific for viral) can also help differentiate ¹,³.