Effects of food colouring added to 2% chlorhexidine gluconate and 70% alcohol for surgical site antisepsis.

Preoperative cleansing of a patient's skin with chlorhexidine gluconate (CHG) in alcohol is superior to cleansing with povidone-iodine for preventing surgical site infection (SSI) after clean-contaminated surgery (Darouilche et al 2010). However, 2% CHG in 70% alcohol, tinted pink, is colourless when applied to limbs for surgery and complete coverage cannot be assured. The purpose of the study was to evaluate the efficacy of food colouring added to CHG in preoperative skin preparation. Two hundred and eight subjects were randomly selected from a population of healthy young adults and were given a questionnaire. They were excluded if they had a known allergy to CHG or food dye, a current infection at the preparation site, or previous preparation with CHG at the site. CHG with food dye additive was applied on the subject's left foot while CHD without the additive was applied on the right. Skin swabs were then taken of both feet and plated on blood agar plates and incubated for 48 hours. Assessment of growth was compared. Patients treated with tinted CHG had around 3.4 times (95% CI: 1.5, 7.8) the risk of a positive bacterial swab compared with those treated with untinted CHG. The efficacy of CHG significantly decreased with food colouring additive. This is consistent with previous studies conducted on similar incompatible substances. In order to have the full efficacy of CHG as a preparation, much thought and care needs to be taken to prevent contamination of the site and substance.