In acute infectious conjunctivitis the general practitioner has to distinguish a bacterial cause from a viral one to select the patients who are most likely to benefit from antibiotic treatment. The doctor makes this distinction on the basis of the presenting signs and symptoms. Additional diagnostic investigations, such as a culture of the conjunctiva, are seldom done, mainly because the result is delayed a few days.
Most treatment trials show that a bacterial pathogen can be isolated from the conjunctiva in only half of patients with clinically diagnosed acute bacterial conjunctivitis. However, general practitioners prescribe antibiotics in most cases of acute infectious conjunctivitis. Although the subject has never been investigated in a primary care setting, studies on suspected acute bacterial conjunctivitis show that topical antibiotics improve the five day remission rate by only 31% compared with placebo.1 Therefore, in a primary care population, more than half of all patients with acute infectious conjunctivitis may receive unnecessary and not always effective antibiotic treatment. This prescription policy may increase the risk of antibiotic resistance, induce side effects, and lead to medicalisation and increases cost.
Can general practitioners differentiate between viral and bacterial conjunctivitis on the basis of signs and symptoms? Major ophthalmological textbooks list several signs and symptoms as being diagnostic for the cause of acute infectious conjunctivitis. The involvement of one eye, followed a few days later by the other eye, and the presence of an enlarged preauricular node are said to be signs indicating a viral cause. The involvement of the other eye within 24-48 hours is said to indicate a bacterial cause. A papillary or (pseudo)membranous conjunctivitis is suggestive of a bacterial origin, whereas a follicular conjunctivitis is said to suggest a viral origin. A mucopurulent or catarrhal discharge is said to be most commonly seen in bacterial or chlamydial conjunctivitis, whereas watery discharge is supposed to be more typical of a viral conjunctivitis.2-4 In most treatment trials on bacterial conjunctivitis the defined criteria for inclusion are purulent or mucopurulent discharge and conjunctival hyperaemia. How evidence based are these assertions? We planned a systematic review to assess the evidence on the diagnostic impact of these and other signs and symptoms.