We thank Liu and coauthors for their interest in our paper and their comments. The primary aims of the paper were to highlight how we investigated the outbreak and the statistical methods we used to determine the outbreak. A secondary aim was to caution about the common fallacy that an absence of proof of effectiveness is the same as proof of ineffectiveness. I believe we fulfilled these aims.
The use of preoperative PVI 5% was common to all surgeons in the unit, and because of the way we organize the service, we know that the contact time is greater than 3 minutes in all patients. Therefore, we are confident that there was something different with my cohort, and the most likely (but not the only possible) factor was the withdrawal of subconjunctival antibiotics. The suggestion that we have been using 2 potentially only partially effective treatments (single instillation of povidone rather than repeated instillation and subconjunctival antibiotics) and that these have somehow summated to give effective prophylaxis is an intriguing one. We wonder where is the evidence for the benefit of a continuous drip of PVI as opposed to a few drops in a normal eye? One of the papers referenced by Liu and coauthors1 looks at the decontamination of donor globes and refers to the “standard” of immersion in antimicrobial for 3 minutes. No provenance is given for that statement. Another of the references papers2 compares PVI concentration, not duration of irrigation, and in that paper bacterial swabs were taken between 1 minute and 2 minutes, not the standard 3 minutes.
It is clear there is a need for further well-controlled studies to determine the best combination of PVI strength, length of time of irrigation, and length of total contact time to achieve the lowest prevalence of bacteria in the operating field for the expected duration of a modern cataract operation.
David Allen FRCOphth
1. Gopinathan U, Reddy MK, Nadkarni MS, et al. Antimicrobial effect of ciprofloxacin, povidone-iodine, and gentamicin in the decontamination of human donor globes. Cornea 1998; 17:57-61
2. Ferguson AW, Scott JA, McGavigan J, et al. Comparison of 5% povidone-iodine solution against 1% povidone-iodine solution in preoperative cataract surgery antisepsis; a prospective randomized double blind study. Br J Ophthalmol 2003; 87:163-167