This is a guest post by Prof Sally Bloomfield…

For many years, “5 log reduction” (LR) has been the gold standard for disinfectant efficacy despite absence of dose:response data linking it to clinical outcomes.  The family of EN tests now used to support claims for disinfectant products has its origins in the European Suspension Test (5LR, 5 mins, 5 test organisms) where 5 LR was probably chosen because it is the limit of sensitivity in an assay where, traditionally, the initial bioburden is 10⁸ colony forming units.  For soap, detergent or dry wiping procedures, until recently their effectiveness has been assumed – possibly on the basis that they produce visible cleanliness? It is only recently that we have had access to efficacy data based on lab models.  A trial of EN 1699 handwashing test showed a mean 2.76 LR when hands contaminated with E .coli are washed with soap.

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