The utility of routine conjunctival swabs in management of conjunctivitis.

Aim: To determine the accuracy of preliminary results of conjunctival swab culture and to evaluate the utility of preliminary and final conjunctival swab culture results in the routine management of conjunctivitis.

Methods: We prospectively identified 164 conjunctival swabs from adults and children over 3 weeks of age and compared preliminary (next day) with final culture results. We modelled the would-be effect on treatment and clinical outcome of three strategies (indiscriminant, delayed and targeted) for management of acute conjunctivitis.

Results: In total, 54 of 164 (33%) samples yielded significant bacterial growth. Compared to final culture, preliminary culture had a sensitivity of 86%, positive predictive value of 98% and specificity of 99%. Modelling showed that an indiscriminant approach to management (all patients given topical antibacterial treatment, no swabs taken) was the most effective at reducing symptoms but led to substantial unnecessary use of topical antibacterial treatment. Modelling showed that a delayed treatment strategy (patients start topical antibacterial treatment only if not improving satisfactorily after 2 days, no swabs taken) was the least effective at reducing symptoms and lead to moderate unnecessary use of topical antibacterial treatment. The targeted treatment strategy (topical antibacterial treatment given to those with clinical predictors of bacterial infection on day 0, positive preliminary culture results on day 1 and positive final culture results on day 2) was highly effective at reducing symptoms and potentially the least wasteful of topical antibacterial treatment.

Conclusion: Preliminary (next day) conjunctival swab culture results are highly predictive of the final result and could be used by practitioners to guide prescription of topical antibacterial treatment.