Handwashing: are experimental models a substitute for clinical trials? Two viewpoints

Methods to evaluate the microbicidal activities of hand-rub and hand-wash agents

In vitro carrier tests, suspension tests, time-kill curves, and determinations of minimum inhibitory concentrations to evaluate the microbicidal activities of hand antiseptics provide only a preliminary indication of the antimicrobial spectrum and speed of action of a given formulation. Ex vivo testing with human or animal skin at human skin temperature and at contact times reflecting field conditions may give a better indication of a formulation's ability to tackle hand-transmitted pathogens. Field testing of hands for levels of skin microbiota before and after antisepsis may be easier to perform, but it is subject to many uncontrollable factors. Whereas randomised clinical trials may be the ultimate approach to assess the effectiveness of hand hygiene protocols and products in preventing microbial cross-transmission and, ultimately, infections, they can be prohibitively expensive, time-consuming, difficult to design, and therefore impractical. Hence, the primary emphasis should be on in vivo testing on human hands, using a well-designed protocol that closely simulates the recommended field use of the formulation, and possibly followed by clinical studies. The use of these method is the most likely to yield useful data on the potential of a formulation to interrupt the spread of pathogens transmitted by hands in healthcare settings. This review provides a critical assessment of the methods currently used to meet regulatory requirements for hand antiseptics in Europe and North America.

Effectiveness of hand-cleansing formulations containing tea tree oil assessed ex vivo on human skin and in vivo with volunteers using European standard EN 1499

The efficacy of formulations containing tea tree oil (TTO) has been assessed in vitro in previous studies. Products that passed the European suspension test guidelines were investigated further in this study, in vivo with volunteers using the European handwashing method (EN 1499) and ex vivo using freshly excised human skin samples. The activity of 5% TTO in 0.001% Tween 80, in a hygienic skin wash (HSW) and in an alcoholic hygienic skin wash (AHSW) was investigated and compared with that of a non-medicated soft soap (SS, control). These formulations were assessed against Escherichia coli K12 as recommended by the European standard. In-vivo results showed that 5% TTO in Tween 80 and the AHSW were significantly more active than the SS after 1 min of handwashing. When assessed ex vivo, these two products were also significantly more active than the reference soap after 1 min of rubbing. Both methods showed that 5% TTO in Tween 80 was generally, although not always, more active than a handwash formulation, and that the AHSW was generally more active than the HSW, although this difference was not significant. The formulations tested, as well as the SS, were more active when assessed in vivo than ex-vivo against E. coli, although only the SS and the HSW were significantly more active in vivo. There appeared to be a pattern in the comparison between ex vivo and in vivo results. The antiseptics tested were, on average, 1.28+/-0.06 times more active when assessed in-vivo than when assessed ex vivo. Nevertheless, the main outcome of the European handwashing method is for the formulation tested to be significantly more active than the SS; both 5% TTO in Tween 80 and the AHSW achieved this both in-vivo and ex-vivo. TTO in Tween 80 and in formulations met the European in-vivo method requirements.

Comparison of two in vivo and two ex vivo tests to assess the antibacterial activity of several antiseptics

An ex vivo test was adapted to mimic the in vivo conditions of testing antiseptic activity on human forearms and in the European Standard Hygienic Handwash Test (BSEN 1499). The study was to validate the ex vivo protocols using 4.8% (w/v) para-chloro-meta-xylenol (PCMX, neat Dettol), 0.5% (w/v) triclosan in 70% (v/v) isopropanol, and 2% (v/v) povidone-iodine against a high bacterial inoculum (>10(8) cfu/mL) of Escherichia coli NCTC 10538. Two ex vivo tests using human skin samples, including one introducing a mechanical rubbing effect, were compared with two corresponding in vivo tests (the forearm test and the BSEN handwashing test). All antiseptics assessed in vivo (forearm and handwash tests) produced reductions in bacterial counts that were significantly greater than those for the non-medicated soft soap control. When assessed ex vivo without rubbing, only PCMX and povidone-iodine achieved reductions significantly greater than soft soap. When assessed ex vivo with mechanical rubbing, only PCMX and triclosan achieved reductions significantly greater than soft soap. Overall, the antiseptics at the concentrations tested were more active when tested in vivo than ex vivo. The addition of a mechanical effect, either in vivo by the volunteers washing their hands or ex vivo by a drill rubbing two skin samples against each other, produced a significantly greater reduction in bacterial concentrations. The ex vivo tests were easily adapted to mimic in vivo protocols. The value of such tests, particularly the one that includes a rubbing effect, may be significant as they avoid the need for human volunteers.

Effects of 4 hand-drying methods for removing bacteria from washed hands: a randomized trial

OBJECTIVE

To evaluate the effects of 4 different drying methods to remove bacteria from washed hands.

SUBJECTS AND METHODS

One hundred adult volunteers participated in this randomized prospective study. All bacterial counts were determined using a modified glove-juice sampling procedure. The difference was determined between the amounts of bacteria on hands artificially contaminated with the bacterium Micrococcus luteus before washing with a nonantibacterial soap and after drying by 4 different methods (cloth towels accessed by a rotary dispenser, paper towels from a stack on the hand-washing sink, warm forced air from a mechanical hand-activated dryer, and spontaneous room air evaporation). The results were analyzed using a nonparametric analysis (the Friedman test). By this method, changes in bacterial colony-forming unit values for each drying method were ranked for each subject.

RESULTS

The results for 99 subjects were evaluable. No statistically significant differences were noted in the numbers of colony-forming units for each drying method (P = .72).

CONCLUSION

These data demonstrate no statistically significant differences in the efficiency of 4 different hand-drying methods for removing bacteria from washed hands.

A risk assessment framework for the evaluation of skin infections and the potential impact of antibacterial soap washing

Antibacterial soaps may have an important role in the control of skin infection. However, quantitative estimation of their benefit is difficult because of the problems associated with conducting epidemiologic studies. An alternative benefit estimation approach, quantitative microbial risk assessment, has application to this problem. This article sets forth the quantitative microbial risk assessment method and applies it specifically to the estimation of the reduction in risk of dermal infection from Staphylococcus aureus resulting from use of antibacterial soaps. A dose-response model was formulated by using available information on growth kinetics of the organism on the skin and dose data based on the inoculation of the forearm skin in volunteers. A predictive relationship for microbial growth on the skin was developed. These data were limited, and clearly more studies are needed on inoculation at more than one site and growth leading to infection on the skin with and without the use of germicidal soaps.However, by using relationships based on extant data sets, it was estimated that the use of germicidal soap could result in a substantial reduction in the risk of infection by S aureus. The estimated risk reduction was in general concordance with published results from epidemiologic studies conducted on military cadets. The methodology of quantitative microbial risk assessment has thus been shown to be applicable to this problem and may have broader applicability in other personal hygiene contexts.

Comparative efficacy of alternative hand-washing agents in reducing nosocomial infections in intensive care units

BACKGROUND

Effective hand-washing can prevent nosocomial infections, particularly in high-risk areas of the hospital. There are few clinical studies of the efficacy of specific hand-cleansing agents in preventing the transmission of pathogens from health care workers to patients.

METHODS

For eight months, we conducted a prospective multiple-crossover trial involving 1894 adult patients in three intensive care units (ICUs). In a given month, the ICU used a hand-washing system involving either chlorhexidine, a broad-spectrum antimicrobial agent, or 60 percent isopropyl alcohol with the optional use of a nonmedicated soap; in alternate months the other system was used. Rates of nosocomial infection and hand-washing compliance were monitored prospectively.

RESULTS

When chlorhexidine was used, there were 152 nosocomial infections, as compared with 202 when the combination of alcohol and soap was used (adjusted incidence-density ratio [IDR], 0.73; 95 percent confidence interval, 0.59 to 0.90). The largest reduction with chlorhexidine was in gastrointestinal infections (IDR, 0.19; 95 percent confidence interval, 0.05 to 0.64). When chlorhexidine was available, the rates of nosocomial infection declined in each of the ICUs, and health care workers washed their hands more often than when alcohol and soap were used (relative risk, 1.28; 95 percent confidence interval, 1.02 to 1.60). The total volume of alcohol and soap used was 46 percent that of chlorhexidine (P less than 0.001).

CONCLUSIONS

A hand-disinfection system using an antimicrobial agent (chlorhexidine) reduces the rate of nosocomial infections more effectively than one using alcohol and soap. The improvement may be explained at least in part by better compliance with hand-washing instructions when chlorhexidine was used.