To The Editor:
I am writing to point out two limitations not mentioned in the study
presented in your article, "Efficacy of Surgical Preparation Solutions
in Foot and Ankle Surgery"
(2005;87:980-5), by Ostrander et
al.
No neutralizing ingredient(s) (neutralizer) was used in the sampling
method, either on the swab or in the transport or 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 preparations (Techni-Care and ChloraPrep) tested.
The second limitation is the sampling method. 3M DuraPrep Surgical Solution
forms a water-insoluble film when it dries. Sampling solution with or without
neutralizer will not dissolve the DuraPrep 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 DuraPrep film
are likely to have come from an area that was not completely prepared or from
some other contamination.
The Food and Drug Administration requires that a surgical preparation in
moist areas, such as the forefoot or inguinal area, reduce the bacterial count
by 3 logs1. In some studies, patients have been found to have 6+
logs2,3 of bacteria in moist sites. Thus, even if a surgical
preparation is doing its job by reducing bacteria by 3 logs, there will still
be residual bacteria remaining.