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

Recommendations for hand hygiene in community settings: a scoping review of current international guidelines

BACKGROUND

Hand hygiene is an important measure to prevent disease transmission.

OBJECTIVE

To summarise current international guideline recommendations for hand hygiene in community settings and to assess to what extent they are consistent and evidence based.

ELIGIBILITY CRITERIA

We included international guidelines with one or more recommendations on hand hygiene in community settings-categorised as domestic, public or institutional-published by international organisations, in English or French, between 1 January 1990 and 15 November 2021.

DATA SOURCES

To identify relevant guidelines, we searched the WHO Institutional Repository for Information Sharing Database, Google, websites of international organisations, and contacted expert organisations and individuals.

CHARTING METHODS

Recommendations were mapped to four areas related to hand hygiene: (1) effective hand hygiene; (2) minimum requirements; (3) behaviour change and (4) government measures. Recommendations were assessed for consistency, concordance and whether supported by evidence.

RESULTS

We identified 51 guidelines containing 923 recommendations published between 1999 and 2021 by multilateral agencies and international non-governmental organisations. Handwashing with soap is consistently recommended as the preferred method for hand hygiene across all community settings. Most guidelines specifically recommend handwashing with plain soap and running water for at least 20 s; single-use paper towels for hand drying; and alcohol-based hand rub (ABHR) as a complement or alternative to handwashing. There are inconsistent and discordant recommendations for water quality for handwashing, affordable and effective alternatives to soap and ABHR, and the design of handwashing stations. There are gaps in recommendations on soap and water quantity, behaviour change approaches and government measures required for effective hand hygiene. Less than 10% of recommendations are supported by any cited evidence.

CONCLUSION

While current international guidelines consistently recommend handwashing with soap across community settings, there remain gaps in recommendations where clear evidence-based guidance might support more effective policy and investment.

Comparison of electric hand dryers and paper towels for hand hygiene: a critical review of the literature

Numerous studies are published on the benefits of electric hand dryers vs paper towels (PT) for drying hands after washing. Data are conflicting and lacking key variables needed to assess infection risks. We provide a rapid scoping review on hand-drying methods relative to hygiene and health risks. Controlled vocabulary terms and keywords were used to search PubMed (1946-2018) and Embase (1947-2018). Multiple researchers independently screened abstracts for relevance using predetermined criteria and created a quality assessment scoring system for relative study comparisons. Of 293 papers, 23 were included in the final analysis. Five studies did not compare multiple methods; however, 2 generally favoured electric dryers (ED); 7 preferred PT; and 9 had mixed or statistically insignificant results (among these, 3 contained scenarios favourable to ED, 4 had results supporting PT, and the remaining studies had broadly conflicting results). Results were mixed among and within studies and many lacked consistent design or statistical analysis. The breadth of data does not favour one method as being more hygienic. However, some authors extended generalizable recommendations without sufficient scientific evidence. The use of tools in quantitative microbial risk assessment is suggested to evaluate health exposure potentials and risks relative to hand-drying methods. We found no data to support any human health claims associated with hand-drying methods. Inconclusive and conflicting results represent data gaps preventing the advancement of hand-drying policy or practice recommendations.

Microbiological Assessment of the Different Hand Drying Methods and Washroom Environment Cross-Contamination

Proper hand drying is a fundamental part of the hand hygiene process looking at optimizing the elimination of potentially pathogenic microbes. This research compared the effectiveness of three different hand drying methods—paper towels, the use of warm air dryers in stationary hands position, and the use of air drying while hand rubbing—and their potential for cross-contamination of other users and the surrounding environment. One hundred sixty samples were collected from finger pads and palms, before and after drying. The outlet of the air dryers, air current emitted from the air dryers, and washroom environment air were also tested. The study reported that paper towels were more successful in eliminating bacteria and lead to less contamination to the washroom environment compared to the air dryers. The average number of bacteria obtained from volunteers using hand air dryer while hand rubbing was significantly higher than drying with air dryer while holding hands stationary. Plates exposed to the turned-off dryer for 5 minutes gave an average of only 25 colonies/plate, while plates exposed to the air outlet of the turned-on warm air dryers provided 292 colonies/plate. Placing Petri dishes at least one meter away from the dryer in the washroom for 30 minutes gave 72.5 colonies/plate. The current research also documented frequent contamination of public washroom environments and showed dissemination of potential pathogens, including Escherichia coli (E. coli), Klebsiella species, Bacillus cereus (B. cereus), Staphylococcus aureus (S. aureus), and coagulase-negative Staphylococci. Over 70.0% of Staphylococci were resistant to at least three antibiotics and 50.0% revealed coresistance to at least four antibiotics including penicillin, erythromycin, clindamycin, and co-trimoxazole. The method of hand drying may serve as a risk factor of cross-contamination from users to the environment and subsequent users and as reservoirs of drug-resistant bacteria in public washrooms.

Achieving Perfect Hand Washing: an Audit Cycle with Surgical Internees

The aim of this study is to achieve 100% compliance in surgical hand antisepsis along with identification of areas of worst compliance and efficacies of various interventions best suited to deal with them. This audit was performed over 6 days in a tertiary care hospital in Calcutta, India, with 42 surgical internees. Compliance to ideal hand washing technique was recorded after each attempt with the first attempt as baseline. Video demonstration, personal demonstration by a consultant, and individual instruction were used as subsequent interventions to achieve 100% compliance. The baseline level of compliance was found to be 33.59%. A total of 6 attempts was required to achieve 100% compliance, with the increase in compliance being statistically significant (p = 0.0294). Personal instruction was found to be the most effective intervention. Hand washing technique was the criterion that needed the most number of attempts (n = 6) to rectify. This study found video-based instruction and individual guidance effective teaching tools for surgical hand disinfection and gave novel data regarding the reasons responsible for poor compliance to proper hand washing in a general surgical setting. This study demonstrated the efficiency of audit cycles in the improvement of surgical hand washing and can be the preferred mode of intervention in future studies aimed at achieving ideal hand antisepsis.

Knowledge Level and Hand Hygiene Practice of Nepalese Immigrants and Their Host Country Population: A Comparative Study

Nepali people are one of the ethnic minority immigrants of Hong Kong. This epidemiological investigation aims to determine and compare the knowledge level and hand hygiene (HH) behaviour of the Nepali people and the population of their host country (i.e., native Chinese population of Hong Kong). A total of 1008 questionnaires were collected via an online platform. The overall knowledge level of the native population towards HH was considerably higher than that of the Nepali respondents. Lower levels of knowledge in young and older people were noted. Reduced HH knowledge was also observed in people with low educational level or with comorbid illness(es). Significant differences between groups were noted in the self-reported hand washing behaviours. Regarding hand drying, more Nepalese than native Chinese respondents always/sometimes dried their hands on their clothing irrespective whether after performing handwashing in public washrooms or at home. Misconceptions and suboptimal practices on HH were prevalent in the two populations. The findings of this comparative study offer valuable information for the development of culturally sensitive health educational programs to enhance HH practices for the ethnic minorities and native Chinese population.

Microbiological evaluation of different hand drying methods for removing bacteria from washed hands

Proper drying of hands after washing is an integral part of hand hygiene. An experimental study on 30 subjects using multiple comparisons of six hand drying methods including 1) drying on own clothes, 2) drying with one paper towel, 3) drying with two paper towels, 4) drying with a warm air dryer while holding hands stationary for 20 s, 5) drying with a warm air dryer while hand rubbing for 20 s, and 6) drying with a jet air dryer until complete dryness was achieved. It aimed to determine the effectiveness of different hand drying methods for removing bacteria from washed hands, so as to identify the optimum method using minimum resources. Our study demonstrated that the use of jet air dryers is the best method to eliminate bacteria on hands, whereas drying hands on one's own clothes is the least effective. Drying hands in a stationary position could remove more bacteria than rubbing hands when using a warm air dryer for 20 s, which mimics people's usual hand-drying practice. No significant difference in bacteria reduction was detected between the use of one or two paper towels for hand drying; therefore, using fewer resources is recommended to maintain environmental sustainability.

Epidemiological investigation on hand hygiene knowledge and behaviour: a cross-sectional study on gender disparity

Background

The hand hygiene (HH) behaviour of the general public and its effect on illnesses are issues of growing importance. Gender is associated with HH behaviour. HH efficiency is a combination of washing efficiency and hand drying, but information about the knowledge level and HH behaviour of the general public is relatively limited. The findings of this cross-sectional study can substantially contribute to the understanding on the knowledge gap and public behaviour towards HH, thereby providing information on gender-specific health promotion activities and campaigns to improve HH compliance.

Methods

An epidemiological investigation by using a cross-sectional study design on the general public was conducted either via an online platform (SurveyMonkey) or paper-and-pen methods. The hand-washing and -drying questionnaire was used for data collection.

Results

A total of 815 valid questionnaires were collected. Majority of the respondents can differentiate the diseases that can or cannot be transmitted with poor HH, but the HH knowledge of the respondents was relatively inadequate. The female respondents had a significantly better HH knowledge than male respondents. The multiple regression analysis results also indicated that females had a significantly higher knowledge score by 0.288 towards HH than males after adjusting for age and education level. Although the majority of the respondents indicated that they performed hand cleaning under different specific situations, they admitted only using water instead of washing their hands with soap. More males than females dried their hands on their own clothing, whereas more females dried their hands through air evaporation. The average time of using warm hand dryers was generally inadequate amongst the respondents.

Conclusions

Being a female, middle-aged and having tertiary education level are protective factors to improve HH knowledge. Misconceptions related to the concepts associated with HH were noted amongst the public. Self-reported practice on hand drying methods indicated that additional education was needed. The findings of this study can provide information on gender-specific health promotion activities and creative campaigns to achieve sustained improvement in HH practices.

The neglected element of hand hygiene - significance of hand drying, efficiency of different methods and clinical implication: A review

Hand hygiene is a fundamental strategy for controlling the spread of infection. Careful hand drying is integral to the process of hand hygiene, which aims to optimise the removal of potentially pathogenic microorganisms. Ineffective hand drying results in wet hands that are an infection risk increasing the potential for cross-infection, occupational contact dermatitis for healthcare practitioners, harm to patients and environmental contamination. Evidence indicates that there has been limited research regarding the significance of hand drying and the efficacy and clinical impact of different drying methods. The purpose of this review paper was to scope and evaluate the existing literature pertaining to hand drying; to examine the clinical consequences associated with wet hands for patients, healthcare practitioners and the clinical environment; to assess the efficacy of different drying methods; to consider the impact on patient safety; and to progress the research, debate and practice relating to hand drying. The methodological framework applied in this review was that of Arksey and O'Malley (2007). Twenty-one papers identified from 112 abstracts screened were included in the review. Analysis identified three primary themes emerging from the literature: (1) efficacy of hand drying methods; (2) drying method and microbial translocation, dispersion and environmental contamination; and (3) drying methods and environmental sustainability. This review highlights the equal importance of hand drying in the process of hand hygiene and suggests that the efficacy of hand drying is a critical factor in the prevention of the transfer of microorganisms to the environment, and from person to person following hand washing. In conclusion, this paper argues that greater attention needs to be given to hand drying in terms of practice, policy and research and its importance in clinical settings given greater focus.

Deposition of Bacteria and Bacterial Spores by Bathroom Hot-Air Hand Dryers

Hot-air hand dryers in multiple men's and women's bathrooms in three basic science research areas in an academic health center were screened for their deposition on plates of (i) total bacteria, some of which were identified, and (ii) a kanamycin-resistant Bacillus subtilis strain, PS533, spores of which are produced in large amounts in one basic science research laboratory. Plates exposed to hand dryer air for 30 s averaged 18 to 60 colonies/plate; but interior hand dryer nozzle surfaces had minimal bacterial levels, plates exposed to bathroom air for 2 min with hand dryers off averaged ≤1 colony, and plates exposed to bathroom air moved by a small fan for 20 min had averages of 15 and 12 colonies/plate in two buildings tested. Retrofitting hand dryers with HEPA filters reduced bacterial deposition by hand dryers ∼4-fold, and potential human pathogens were recovered from plates exposed to hand dryer air whether or not a HEPA filter was present and from bathroom air moved by a small fan. Spore-forming colonies, identified as B. subtilis PS533, averaged ∼2.5 to 5% of bacteria deposited by hand dryers throughout the basic research areas examined regardless of distance from the spore-forming laboratory, and these were almost certainly deposited as spores. Comparable results were obtained when bathroom air was sampled for spores. These results indicate that many kinds of bacteria, including potential pathogens and spores, can be deposited on hands exposed to bathroom hand dryers and that spores could be dispersed throughout buildings and deposited on hands by hand dryers.IMPORTANCE While there is evidence that bathroom hand dryers can disperse bacteria from hands or deposit bacteria on surfaces, including recently washed hands, there is less information on (i) the organisms dispersed by hand dryers, (ii) whether hand dryers provide a reservoir of bacteria or simply blow large amounts of bacterially contaminated air, and (iii) whether bacterial spores are deposited on surfaces by hand dryers. Consequently, this study has implications for the control of opportunistic bacterial pathogens and spores in public environments including health care settings. Within a large building, potentially pathogenic bacteria, including bacterial spores, may travel between rooms, and subsequent bacterial/spore deposition by hand dryers is a possible mechanism for spread of infectious bacteria, including spores of potential pathogens if present.

Bacteriological Aspects of Hand Washing: A Key for Health Promotion and Infections Control

The aim of this review is to show the historical aspects of hands washing for healthy life and explains how can reduce the transmission of community-acquired infectious agents by healthcare workers and patients. This review article is prepared based on available database. The key words used were hands washing, risk assessment, hands hygiene, bacterial flora, contamination, infection, nosocomial, tap water, sanitizer, bacterial resistance, hands bacterial flora, washing methods, antiseptics, healthcare workers, healthcare personnel, from PubMed, ScienceDirect, Embase, Scopus, Web of Sciences, and Google Scholar. Data were descriptively analyzed. The insistence on hand washing has a history of 1400 years. The research results indicate that the bacteria released from the female washed hands in wet and dry condition was lower than from the male's hands with a significance level (3 CFU vs. 8 CFU; confidence interval 95%, P ≤ 0.001). The valuable results of the study indicated that released amount of bacterial flora from wet hands is more than 10 times in compared to dry hands. In addition, established monitoring systems for washing hands before and after patient's manipulation as well as after toilet were dominant indices to prevent the transfer of infectious agents to the patients. Increasing awareness and belief of the healthcare workers have shown an important role by about 30% reduction in the transfection. Hand washing could reduce the episodes of transmission of infectious agents in both community and healthcare settings. However, hand washing is an important key factor to prevent transmission of infectious agents to patients. There is no standard method for measuring compliance. Thus, permanent monitoring of hand washing to reduce the transmission of infections is crucial. Finally, the personnel must believe that hand washing is an inevitable approach to infection control.

Assessment of the bacterial contamination of hand air dryer in washrooms

The present study was carried out, using standard techniques, to identify and count the bacterial contamination of hand air dryers, used in washrooms. Bacteria were isolated from the air flow, outlet nozzle of warm air dryers in fifteen air dryers used in these washrooms. Bacteria were found to be relatively numerous in the air flows. Bacterially contaminated air was found to be emitted whenever a warm air dryer was running, even when not being used for hand drying. Our investigation shows that Staphylococcus haemolyticus, Micrococcus luteus, Pseudomonas alcaligenes, Bacillus cereus and Brevundimonad diminuta/vesicularis were emitted from all of the dryers sampled, with 95% showing evidence of the presence of the potential pathogen S. haemolyticus. It is concluded that hot air dryers can deposit pathogenic bacteria onto the hands and body of users. Bacteria are distributed into the general environment whenever dryers are running and could be inhaled by users and none-users alike. The results provide an evidence base for the development and enhancement of hygienic hand drying practices.

epic3: national evidence-based guidelines for preventing healthcare-associated infections in NHS hospitals in England

National evidence-based guidelines for preventing healthcare-associated infections (HCAI) in National Health Service (NHS) hospitals in England were originally commissioned by the Department of Health and developed during 1998-2000 by a nurse-led multi-professional team of researchers and specialist clinicians. Following extensive consultation, they were first published in January 2001(1) and updated in 2007.(2) A cardinal feature of evidence-based guidelines is that they are subject to timely review in order that new research evidence and technological advances can be identified, appraised and, if shown to be effective for the prevention of HCAI, incorporated into amended guidelines. Periodically updating the evidence base and guideline recommendations is essential in order to maintain their validity and authority. The Department of Health commissioned a review of new evidence and we have updated the evidence base for making infection prevention and control recommendations. A critical assessment of the updated evidence indicated that the epic2 guidelines published in 2007 remain robust, relevant and appropriate, but some guideline recommendations required adjustments to enhance clarity and a number of new recommendations were required. These have been clearly identified in the text. In addition, the synopses of evidence underpinning the guideline recommendations have been updated. These guidelines (epic3) provide comprehensive recommendations for preventing HCAI in hospital and other acute care settings based on the best currently available evidence. National evidence-based guidelines are broad principles of best practice that need to be integrated into local practice guidelines and audited to reduce variation in practice and maintain patient safety. Clinically effective infection prevention and control practice is an essential feature of patient protection. By incorporating these guidelines into routine daily clinical practice, patient safety can be enhanced and the risk of patients acquiring an infection during episodes of health care in NHS hospitals in England can be minimised.

A qualitative evaluation of hand drying practices among Kenyans

BACKGROUND

Recommended disease prevention behaviors of hand washing, hygienic hand drying, and covering one's mouth and nose in a hygienic manner when coughing and sneezing appear to be simple behaviors but continue to be a challenge to successfully promote and sustain worldwide. We conducted a qualitative inquiry to better understand current hand drying behaviors associated with activities of daily living, and mouth and nose covering practices, among Kenyans.

METHODS AND FINDINGS

We conducted 7 focus group discussions; 30 in-depth interviews; 10 structured household observations; and 75 structured observations in public venues in the urban area of Kisumu; rural communities surrounding Kisumu; and a peri-urban area outside Nairobi, Kenya. Using a grounded theory approach, we transcribed and coded the narrative data followed by thematic analysis of the emergent themes. Hand drying, specifically on a clean towel, was not a common practice among our participants. Most women dried their hands on their waist cloth, called a leso, or their clothes whether they were cooking, eating or cleaning the nose of a young child. If men dried their hands, they used their trousers or a handkerchief. Children rarely dried their hands; they usually just wiped them on their clothes, shook them, or left them wet as they continued with their activities. Many people sneezed into their hands and wiped them on their clothes. Men and women used a handkerchief fairly often when they had a runny nose, cold, or the flu. Most people coughed into the air or their hand.

CONCLUSIONS

Drying hands on dirty clothes, rags and lesos can compromise the benefits of handwashing. Coughing and sneezing in to an open hand can contribute to spread of disease as well. Understanding these practices can inform health promotion activities and campaigns for the prevention and control of diarrheal disease and influenza.

The hygienic efficacy of different hand-drying methods: a review of the evidence

The transmission of bacteria is more likely to occur from wet skin than from dry skin; therefore, the proper drying of hands after washing should be an integral part of the hand hygiene process in health care. This article systematically reviews the research on the hygienic efficacy of different hand-drying methods. A literature search was conducted in April 2011 using the electronic databases PubMed, Scopus, and Web of Science. Search terms used were hand dryer and hand drying. The search was limited to articles published in English from January 1970 through March 2011. Twelve studies were included in the review. Hand-drying effectiveness includes the speed of drying, degree of dryness, effective removal of bacteria, and prevention of cross-contamination. This review found little agreement regarding the relative effectiveness of electric air dryers. However, most studies suggest that paper towels can dry hands efficiently, remove bacteria effectively, and cause less contamination of the washroom environment. From a hygiene viewpoint, paper towels are superior to electric air dryers. Paper towels should be recommended in locations where hygiene is paramount, such as hospitals and clinics.

Hand washing among school children in Bogotá, Colombia

OBJECTIVES

We assessed hand-washing behaviors and intentions among school children in Bogotá, Colombia, to help identify and overcome barriers to proper hygiene practices.

METHODS

Data on hand-washing behavior and intentions and individual and contextual factors were collected from 2042 sixth- through eighth-grade students in 25 schools in Bogotá via anonymous questionnaires. A member of the school administration or teaching staff completed a questionnaire about the school environment. Site inspections of bathroom facilities were conducted.

RESULTS

Only 33.6% of the sample reported always or very often washing hands with soap and clean water before eating and after using the toilet. About 7% of students reported regular access to soap and clean water at school. A high level of perceived control was the strongest predictor of positive hand-washing intentions (adjusted odds ratio [AOR]=6.0; 95% confidence interval [CI]=4.8, 7.5). Students with proper hand-washing behavior were less likely to report previous-month gastrointestinal symptoms (OR=0.8; 95% CI=0.6, 0.9) or previous-year school absenteeism (OR=0.7; 95% CI=0.6, 0.9).

CONCLUSIONS

Scarcity of adequate facilities in most schools in Bogotá prevents children from adopting proper hygienic behavior and thwarts health promotion efforts. The current renovation program of public schools in Bogotá provides a unique opportunity to meet the challenges of providing a supportive environment for adoption of healthy behaviors.

epic2: National evidence-based guidelines for preventing healthcare-associated infections in NHS hospitals in England

National evidence-based guidelines for preventing healthcare-associated infections (HCAI) in National Health Service (NHS) hospitals in England were commissioned by the Department of Health (DH) and developed during 1998-2000 by a nurse-led multi-professional team of researchers and specialist clinicians. Following extensive consultation, they were published in January 2001. These guidelines describe the precautions healthcare workers should take in three areas: standard principles for preventing HCAI, which include hospital environmental hygiene, hand hygiene, the use of personal protective equipment, and the safe use and disposal of sharps; preventing infections associated with the use of short-term indwelling urethral catheters; and preventing infections associated with central venous catheters. The evidence for these guidelines was identified by multiple systematic reviews of experimental and non-experimental research and expert opinion as reflected in systematically identified professional, national and international guidelines, which were formally assessed by a validated appraisal process. In 2003, we developed complementary national guidelines for preventing HCAI in primary and community care on behalf of the National Collaborating Centre for Nursing and Supportive Care (National Institute for Healthand Clinical Excellence). A cardinal feature of evidence-based guidelines is that they are subject to timely review in order that new research evidence and technological advances can be identified, appraised and, if shown to be effective in preventing HCAI, incorporated into amended guidelines. Periodically updating the evidence base and guideline recommendations is essential in order to maintain their validity and authority. Consequently, the DH commissioned a review of new evidence published following the last systematic reviews. We have now updated the evidence base for making infection prevention and control recommendations. A critical assessment of the updated evidence indicated that the original epic guidelines published in 2001 remain robust, relevant and appropriate but that adjustments need to be made to some guideline recommendations following a synopsis of the evidence underpinning the guidelines. These updated national guidelines (epic2) provide comprehensive recommendations for preventing HCAI in hospitals and other acute care settings based on the best currently available evidence. Because this is not always the best possible evidence, we have included a suggested agenda for further research in each section of the guidelines. National evidence-based guidelines are broad principles of best practice which need to be integrated into local practice guidelines. To monitor implementation, we have suggested key audit criteria for each section of recommendations. Clinically effective infection prevention and control practice is an essential feature of protecting patients. By incorporating these guidelines into routine daily clinical practice, patient safety can be enhanced and the risk of patients acquiring an infection during episodes of healthcare in NHS hospitals in England can be minimised.

The effects of test variables on the efficacy of hand hygiene agents

BACKGROUND

Hand hygiene is essential to interrupting disease transmission in health care facilities. Multiple hand hygiene agents are currently available for use in the health care setting. To evaluate the utility of these agents, both the user acceptability and the efficacy need to be evaluated. Different hand hygiene test methodologies have been used to measure the efficacy of these agents, but efficacy results vary depending on variations to key parameters in these methodologies. The purpose of this study was to evaluate the effect of test variables on the efficacy of hand hygiene agents.

METHODS

Both a comprehensive literature review and original hand hygiene efficacy studies were undertaken. The literature review was conducted using a Medline search, and hand hygiene efficacy studies were conducted under the American Society for Testing and Materials (ASTM). E 1174 Standard Test Method for Evaluation of the Effectiveness of Health Care Personnel Handwash Formulation.

RESULTS

The literature review and our original data showed that the following variables affected the hand hygiene efficacy measurements: hand jewelry, experimental contamination versus normal flora, method of application of test organism, hand hygiene agent, concentration of active ingredient, volume of hand hygiene agent, duration of application of hand hygiene agent, method of application of hand hygiene agent, and study method (human challenge trial versus in vitro suspension test).

CONCLUSIONS

Although many methodological variables affect efficacy results, infection control professionals in their analysis of product information should always assess the results in light of the following key variables: concentration and type of active ingredient, duration of exposure to hand hygiene agent, volume of hand hygiene agent applied, test organism, and study method (ie, human challenge vs. in vitro suspension test).