The precautionary principle: what is the risk of reusing disposable drops in routine ophthalmology consultations and what are the costs of reducing this risk to zero?

BACKGROUND: Instilling eye drops is a ubiquitous procedure in eye clinics. This audit aimed to assess the risk of contamination of disposable droppers and to quantify the financial and waste implications of reducing this risk to zero by using disposable droppers only once.
METHODS: A total of 100 disposable Minims were used to place one drop in each eye of 70 patients. The dropper tip was then cultured for aerobic and anaerobic microbes.
RESULTS: Coagulase-negative staphylococcus was cultured from five samples. The contamination rate per drop application was 2.5%. The risk of cross-contamination with coagulase-negative staphylococcus would be between 1 : 400 and 1 : 80 if the bottle was reused once or six times. Reducing this risk to zero costs between pound2.75 and pound4.6 million per annum and generates between 6.85 and 11.42 more tonnes of paper waste and between 12.69 and 21.15 more tonnes of plastic waste than a strategy that reuses the disposable dropper.
CONCLUSION: Reducing the risk of dropper contamination and subsequent cross infection has financial and environmental costs. As exposure to coagulase-negative staphylococcus is not necessarily associated with infection, it would be useful to decide acceptable risk levels for a given cost to maximise both cost-effectiveness and patient safety.