WHO Guidelines on Hand Hygiene in Health Care - Safe Care ...

PART I. REVIEW OF SCIENTIFIC DATA RELATED TO HAND HYGIENE
10.
Methods to evaluate the antimicrobial efficacy of
handrub and handwash agents and formulations
for surgical hand preparation
With the exception of non-medicated soaps, every new formulation for hand antisepsis should be tested for its
antimicrobial efficacy to demonstrate that: (i) it has superior efficacy over normal soap; or (ii) it meets an agreed
performance standard. The formulation with all its ingredients should be evaluated to ensure that humectants
or rehydrating chemicals added to ensure better skin tolerance do not in any way compromise its antimicrobial
action.
Many test methods are currently available for this purpose, but
some are more useful and relevant than others. For example,
determination of the minimum inhibitory concentration (MIC) of
such formulations against bacteria has no direct bearing on the
“killing effect” expected of such products in the field. Conditions
in suspension and in vitro 192 or ex vivo 193 testing do not reflect
those on human skin. Even simulated-use tests with subjects
are considered by some as “too controlled”, prompting testing
under in praxi or field conditions. Such field testing is difficult to
control for extraneous influences. In addition, and importantly,
the findings of field tests provide scant data on a given
formulation’s ability to cause a measurable reduction in handtransmitted
nosocomial infections. While the ultimate approach
in this context would be clinical trials, they are generally quite
cumbersome and expensive. For instance, power analysis
reveals that for demonstrating a reduction in hand-transmitted
infections from 2% to 1% by changing to a presumably better
hand antiseptic agent, almost 2500 subjects would be required
in each of two experimental arms at the statistical pre-settings
of (unidirectional) = 0.05 and a power of 1- = 0.9. 194 For this
reason, the number of such trials remains quite limited. 195-197
To achieve a reduction from 7% to 5% would require 3100
subjects per arm. This reinforces the utility of well-controlled,
economically affordable, in vivo laboratory-based tests to
provide sufficient data to assess a given formulation’s potential
benefits under field use.
10.1 Current methods
Direct comparisons of the results of in vivo efficacy testing of
handwashing, antiseptic handwash, antiseptic handrub, and
surgical hand antisepsis are not possible because of wide
variations in test protocols. Such variations include: (i) whether
hands are purposely contaminated with a test organism before
use of the test agent; (ii) the method used to contaminate
fingers or hands; (iii) the volume of hand hygiene product
applied; (iv) the time the product is in contact with the skin; and
(v) the method used to recover the organism from the skin after
the test formulation has been used.
Despite the differences noted above, most testing falls into one
of two major categories. One category is designed to evaluate
handwash or handrub agents to eliminate transient pathogens
from HCWs’ hands. In most such studies, the subjects’ hands
are experimentally contaminated with the test organism before
applying the test formulation. In the second category, which
applies to pre-surgical scrubs, the objective is to evaluate the
test formulation for its ability to reduce the release of naturally
present resident flora from the hands. The basic experimental
design of these methods is summarized below and the
procedures are presented in detail in Table I.10.1.
In Europe, the most commonly used methods to test
hand antiseptics are those of the European Committee
for Standardization (CEN). In the USA and Canada, such
formulations are regulated by the Food and Drug Administration
(FDA) 198 and Health Canada, respectively, which refer to the
standards of ASTM International (formerly, the American Society
for Testing and Materials).
It should be noted that the current group of experts
recommends using the term “efficacy” to refer to the (possible)
effect of the application of a hand hygiene formulation when
tested in laboratory or in vivo situations. By contrast, it would
recommend using the term “effectiveness” to refer to the clinical
conditions under which hand hygiene products have been
tested, such as field trials, where the impact of a hand hygiene
formulation is monitored on the rates of cross-transmission of
infection or resistance. 199
10.1.1 Methods to test activity of hygienic handwash and
handrub agents
The following in vivo methods use experimental contamination
to test the capacity of a formulation to reduce the level of
transient microflora on the hands without regard to the resident
flora. The formulations to be tested are hand antiseptic agents
intended for use by HCWs, except in the surgical area.
CEN standards: EN 1499 and EN 1500
In Europe, the most common methods for testing hygienic
hand antiseptic agents are EN 1499 200 and EN 1500. 201 Briefly,
the former standard requires 12–15 subjects, and the latter
(in the forthcoming amendment) 18–22, and a culture of E.
coli. Subjects are assigned randomly to two groups where
one applies the test formulation and the other a standardized
reference solution. In a consecutive run, the two groups reverse
roles (cross-over design).
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