Efficacy of surgical hand scrub products based on chlorhexidine is largely overestimated without neutralizing agents in the sampling fluid

Background Surgical hand antiseptics often contain chlorhexidine gluconate (CHG). There are doubts that the full effect measured for these products might only be achieved after sampling because of a lack of valid neutralizing agents (NAs) in the sampling fluid. Methods We measured the efficacy of Avagard CHG and Hibiclens for 11 applications over 5 days according to the manufacturers' instructions. NAs were added to the sampling fluid and the dilution fluid (group 1) or to only the dilution fluid (group 2). In a third group, NAs were added to the dilution fluid only, and cream was applied after the final scrub on days 1 to 4. Neutralization was validated according to American Society for Testing and Materials International standard 1054 using Staphylococcus epidermidis . Results When NAs were not added to the sampling fluid, both products were very effective, with a mean log 10 reduction in flora of 3.32 ± 0.53 for Avagard and 3.68 ± 0.52 for Hibiclens on day 5. When NAs were included in the sampling fluid, however, the immediate efficacy was significantly lower, at 2.75 ± 0.55 and 3.14 ± 0.50, respectively. A lack of NAs in the sampling fluid resulted in overestimation of efficacy by a factor of between 0.3 and 1.1 log 10 . Conclusion Efficacy studies carried out without NAs in the sampling fluid for products with CHG should be critically assessed.