Purpose: Povidone-Iodine (PI) 5-10% remains the gold standard for reducing ocular surface bacteria in preparation for intravitreal injection, however a significant number of patients become intolerant due to corneal toxicity. With the need for repetitive injections, clinicians have sought to dilute PI. The aim of this study is to investigate the effect of diluted PI on bacteria dispersal associated with speech.
Method: Volunteer subjects read a standardised script for 5 minutes over a blood agar plate positioned 20cm in front in a simulated position of an intravitreal injection procedure. The blood agar plates were subject to (randomized): 1% PI; 2.5% PI; 5% PI; no additional application (control). The plates were incubated at 37OC for 72 hours and the number of Colony Forming Units (CFUs) was determined.
Results: A total of 21 volunteers participated. Control plates had a median growth of 25 CFUs (IQR:15-40), 1% PI plates had a median growth of 30 CFUs (range:15-82), 2.5% PI had a median growth of 18 CFUs (IQR:10-43) and 5% PI had a median growth of 2 CFUs (IQR:0-5). Significantly less bacterial growth occurred at 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 decreasing colony count as PI concentration increased (P<0.001).
Conclusion: PI concentrations less than 5% are not significantly effective at reducing bacterial growth associated with bacterial dispersal from speech. When using PI for pre-injection antisepsis, diluting to concentrations less than 5% should be avoided.