QUANTITATIVE BACTERIOLOGICAL ASSESSMENT O F A DONOR SKIN DISINFECTIONMETHOD

Skin disinfection at the site of venipuncture is a critical point in e very blood transfusion collection procedure, as it contributes to ensu re the bacterial safety of transfusion. Quantitative and qualitative a nalysis of bacteria present in the antecubital fossae before and after skin disinfection may be one method of assessing the anti-bacterial e fficiency of disinfection. Swab culture systems and contact plates are the two techniques usually employed for this purpose. A washing and s wabbing technique was used to quantify bacteria before and after skin disinfection of the antecubital fossae in blood donors. This contra-pl acebo study was carried out on 32 donors, each of whom served as his o wn control, with a random choice of test arm and opposing control arm. Bacterial counts were determined in the antecubital fossae without sk in disinfection (control, n = 32) and after a 3 step skin preparation procedure (cleaning, wiping, disinfection) using placebo (distilled wa ter, n = 16) or an antiseptic product (mixture of chlorexidine, benzal konium chloride and benzylic alcohol, n = 16). The absence of a statis tical difference in bacterial counts between the right and left antecu bital fossae without disinfection was controlled in a preliminary stud y of 20 subjects. Mean bacterial counts were 25,000/cm(2) and 27,400/c m(2) respectively for aerobic and anaerobic bacteria before disinfecti on, with a wide variation in results between individuals. When using p lacebo, preparation of the venipuncture site by the 3 step method (cle aning, wiping, disinfection) resulted in a non significant mean reduct ion of 0.56 log in aerobic and anaerobic bacteria. Using the antisepti c product, the same method resulted in a significant mean reduction of 1.8 and 1.7 log respectively in aerobic (p = 0.015) and anaerobic flo ra (p = 0.005). On an average, 2,750 aerobic bacteria/cm(2) and 2,910 anaerobic bacteria/cm(2) remained after disinfection, while qualitativ e analysis showed that disinfection suppressed the transitory flora in all cases but left part of the resident flora in 12/16 cases. These f indings are comparable to those of other studies carried out to evalua te this kind of technique for the disinfection of operation sites. In comparison with other techniques classically employed for this type of evaluation (swab systems or contact plates), the method used in this study has the advantage of allowing the quantification of the reductio n in bacteria. Hence this method could be employed for comparative ass essment of skin disinfection techniques with the aim of improving thei r anti-bacterial efficiency and could also make possible the definitio n of a minimum bacterial count (resident flora) to be obtained in all cases after disinfection.