The effect of diluting povidone-iodine on bacterial growth associated with speech

Povidone-Iodine (PI) may be diluted when used as an antiseptic prior to an intravitreal injection in an attempt to decrease patient discomfort. This study aims to investigate the effect of diluting povidone-iodine (PI) on bacterial growth from bacterial droplet dispersal associated with speech.

Participants read a standardised script for 5 min over a blood agar plate positioned at 20 cm in a simulated position of an intravitreal injection procedure. The blood agar plates were subject to a randomised pre-application of 1% PI; 2.5% PI; 5% PI and no pre-application (control). The plates were incubated at 37 °C for 72 h and the number of Colony Forming Units (CFUs) was determined. CFUs were summarised as median and interquartile range (IQR). Wilcoxon rank sum test was used to assess pairwise comparisons of the various PI concentrations to the control group. Any trend across PI concentration was assessed using Kendall's tau rank correlation.

Twenty-one subjects participated. Control plates had a median growth of 25 CFUs (interquartile range [IQR]:15-40), 1% PI plates had a median growth of 30 CFUs (IQR:15-82), 2.5% PI had a median growth of 18 CFUs (IQR:10-32) and 5% PI had a median growth of 2 CFUs (IQR:0-5). There was significantly less bacterial growth with 5% PI compared to control (P < 0.001). Bacterial growth at 2.5% PI and 1% PI did not differ significantly from control. There was a statistically significant trend for decreasing colony count as PI concentration increased (P < 0.001).

PI concentrations less than 5% are not effective at reducing bacterial growth from bacterial droplet dispersal associated with speech. When using PI for pre-injection antisepsis, concentrations below 5% should be avoided.