A Method to Test the Efficacy of Handwashing for the Removal of Emerging Infectious Pathogens

Summary

Handwashing is widely recommended to prevent infectious disease transmission. However, there is little evidence on which handwashing methods are most efficacious at removing infectious disease pathogens. We developed a method to assess the efficacy of handwashing methods at removing microorganisms.

Abstract

Handwashing is widely recommended to prevent infectious disease transmission. However, little comparable evidence exists on the efficacy of handwashing methods in general. Additionally, little evidence exists comparing handwashing methods to determine which are most efficacious at removing infectious pathogens. Research is needed to provide evidence for the different approaches to handwashing that may be employed during infectious disease outbreaks. Here, a laboratory method to assess the efficacy of handwashing methods at removing microorganisms from hands and their persistence in rinse water is described. Volunteers' hands are first spiked with the test organism and then washed with each handwashing method of interest. Generally, surrogate microorganisms are used to protect human subjects from disease. The number of organisms remaining on volunteers' hands after washing is tested using a modified "glove juice" method: the hands are placed in gloves with an eluent and are scrubbed to suspend the microorganisms and make them available for analysis by membrane filtration (bacteria) or plaque assay (viruses/bacteriophages). Rinse water produced from the handwashing is directly collected for analysis. Handwashing efficacy is quantified by comparing the log reduction value between samples taken after handwashing to samples with no handwashing. Rinse water persistence is quantified by comparing rinse water samples from various handwashing methods to samples collected after handwashing with just water. While this method is limited by the need to use surrogate organisms to preserve the safety of human volunteers, it captures aspects of handwashing that are difficult to replicate in an in vitro study and fills research gaps on handwashing efficacy and the persistence of infectious organisms in rinse water.

Introduction

Handwashing is widely recommended to prevent the spread of disease, particularly those transmitted by the fecal-oral or airborne route, including diarrheal and respiratory diseases¹. Surprisingly, there is little comparable evidence on the efficacy of handwashing methods, such as handwashing with soap and water (HWWS) and with alcohol-based hand sanitizer (ABHS), on the removal of organisms from the hands. Initial research has found that the mechanical action of handwashing, as opposed to the handwashing method, may account for most organism removal^2,3. Additionally, there is little com....

Protocol

Ethics Statement: The study described here (on Phi6 and E. coli as surrogates for Ebola) was approved by the Institutional Review Board at Tufts Medical Center and Tufts University Health Sciences Campus (#12018); Harvard University ceded review to the Tufts Institutional Review Board.

NOTE: Prior to beginning this protocol, two steps must be completed. First, a Biosafety Level 1 (BSL-1) surrogate or non-infectious version of the pathogen to be studied that is safe to use on human subjects must be identified and selected³⁰. A BSL-1 surrogate or non-infectious pathogen is necessary for this protocol, as the o....

Results

Here, the protocol (Figure 1) was completed with 18 volunteers, who were each tested using both E. coli and Phi6. Significant differences were found between handwashing results with E. coli both with and without soil load and Phi6 with soil load (Figure 2 and Figure 3). For E. coli without soil load, handwashing with HTH, NaDCC, and stabilized NaOCl all resulted in signific.......

Discussion

The method described here provides an approach for testing handwashing efficacy in a controlled laboratory setting. This method highlights the use of human volunteers and surrogate, non-infectious organisms. Using the method, it was possible to demonstrate differences in: 1) the efficacy of handwashing methods and 2) organism persistence in rinse water. The purpose of presenting this protocol is to provide a general framework that can be adapted to test a wide range of surrogate organisms and handwashing methods relevant.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Soap bar	Dove	White Beauty Bar soap
Alcohol-based hand sanitizer	Purell	Advanced Instant Hand Sanitizer with 70% Ethyl Alcohol
HTH Powder	Acros Organics	300340010
NaDCC Powder	Medentech	Klorsept granules
NaOCl Solution	Acros Organics	419550010
Electrochlorinator	AquaChlor
Iodometric titrator	Hach	1690001
Bovine serum albumin	MP Biomedicals	NC0117242
Tryptone	Fisher	BP1421-100
Bovine Mucin	EMD Milipore	49-964-3500MG
0.22 µm Filter	EMD Milipore	GVWP04700
NaCl	Fisher	BP358-1
Skin pH probe	Hanna Instruments	H199181
Large Whirlpak Sample Bag	Nasco	B01447WA
Small Whirlpak Sample Bag	Nasco	B01323WA
Funnel bottle	Thermo Scientific	3120850001	You may drill an appropriately sized hole in the lid of a bottle to form a funnel that will dispense water at the appropriate flow rate
Ethanol	ThermoScientific	615090010	Mix with water to produce 70% ethanol
Spray bottle	Qorpak	PLC06934
E. coli	ATCC	25922
LB Broth	Fisher BioReagents	BP1426-2
LB Agar	Fisher BioReagents	BP1425-500
Sterile loop	Globe Scientific	22-170-204
Phi6	HER	102
Nutrient broth	BD Difco	BD 247110
GeneQuant 100 Spectrophotometer	General Electric	28-9182-04
Sodium thiosulfate	Fisher Chemical	S445-3
Membrane filter (47 mm, 0.45 µm)	EMD Millipore	HAWP04700
m-ColiBlue24 broth media	EMD Millipore	M00PMCB24
Petri dish with pad (47 mm)	Fisherbrand	09-720-500
Vacuum Manifold	Thermo Scientific/Nalgene	09-752-5
Filter funnels	Thermo Scientific/Nalgene	09-747
Pseudomonas syringae	HER	1102
Phosphate Buffered Saline	Thermo Scientific	10010031	Solution may also be mixed from source compounds according to any basic recipe