We appreciate the comments that were made regarding our recent study, which allows me to explain our methodology in more detail.

Cultures were obtained several minutes after the prep solution was applied. Dry, sterile, cotton-tipped swabs were used to sample the skin. We did not moisten the swabs with saline or water. By the time the cultures were obtained, all prep solutions had dried on the skin. The swabs were therefore passed over the skin which was covered by a dried film of prep solution. Again, the swabs were dry. The water-soluble preps (Techni-Care and ChloraPrep) were no more likely than the water- insoluble prep (DuraPrep) to be absorbed onto the swab and there was no visible prep solution on the swabs after obtaining the cultures. Therefore, the lack of a neutralizer should not have inflated the efficacy of the water-soluble preps relative to the water-insoluble prep tested. In fact, the addition of a neutralizer may have falsely elevated the kill rates for DuraPrep. It has been suggested that the water-insoluble polymer may shield the antimicrobial from the neutralizer, rendering the neutralizer ineffective. Finally, the dry swabs were placed into transport media and were carried immediately to the lab for processing, decreasing the time for any further bacterial kill.

To address Dr.Rittle's second comment, the swabs were not moistened prior to sampling the skin. The prep solutions had dried. Therefore, the sampling methods were comparable for all three solutions tested. Given the very visible, yellow coloration of the DuraPrep solution, we were certain that the foot and ankle was thoroughly and completely prepped. No swabs were taken from un-prepped areas on the skin. The suggestion that the DuraPrep positive cultures were the result of some unknown contamination is very unlikely. The positive cultures were consistent with the native microflora found on the foot and ankle.

Finally, we understand that the FDA has minimum requirements for pre- surgical skin preparation solutions. It is our feeling, however, that the goal of presurgical preparation should be to reduce the bacterial load as much as possible in an effort to limit potentially devastating postoperative infections. In the current study, the combination of chlorhexidine and alcohol (ChloraPrep) was the most efficacious of the three solutions tested in eliminating bacteria from the forefoot prior to surgery.

To the Editor:

I am writing to point out 2 limitations not mentioned in the study presented in your May, 2005, article “Efficacy of surgical preparation solutions in foot and ankle surgery” by Ostrander, et al.

No neutralizing ingredient(s) (neutralizer) was/were used in the sampling method, either on the swab, in the transport media, or the culture media. American Society for Testing and Materials (ASTM) method E1054-02 recommends adding appropriate neutralizers to the solution used for sampling skin. A neutralizer inactivates an antimicrobial at sampling so that there is no further kill in the test tube while the sample is waiting to be diluted and plated for quantification. If a neutralizer is not present, the antimicrobial will continue to kill bacteria in vitro resulting in an erroneous higher kill rate. The lack of a neutralizer would inflate the efficacy of the water-soluble preps (Techni-Care@ and ChloraPrep@) tested.

The second limitation is the sampling method. 3Mâ„¢ DuraPrepâ„¢ Surgical Solution forms a water insoluble film when it dries. Sampling solution with or without neutralizer will not dissolve the DuraPrepTM film to allow sampling of the skin beneath. Since the other antimicrobials are water soluble, the sampling method is not consistent between products. Any bacteria sampled from DuraPrepTM film are likely to have come from an area that was not completely prepped or from some other contamination.

FDA requires that a surgical prep in moist areas – such as the forefoot or inquinal area – reduce bacterial count by 3 logs(1). In some studies, patients have been found to have 6+ logs(2,3) of bacteria in moist sites. So even if a surgical prep is doing its job by reducing bacteria by 3 logs, there will still be residual bacteria remaining.

References:

(1) Health-Care Antiseptic Drug Product Tentative Final Monograph, Proposed Rule, 59 Federal Register, p. 31402-31452 (Friday, June 17, 1994).

(2) Jeng, D.K. and J.E. Severin. Povidone iodine gel alcohol: a 30-second, onetime application preoperative skin preparation. Am J Infect Control 26: 488-494, 1998.

(3) 3M internal data.