Hand washing can slow down the spread of infectious diseases


A new study estimates that improving the rates of handwashing by travelers passing through just 10 of the world’s leading airports could significantly reduce the spread of many infectious diseases.

And the greater the improvement in people’s handwashing habits at airports, the more dramatic the effect on slowing the disease, the researchers found.

The findings, which deal with infectious diseases in general including the flu, were published in late December, just before the recent coronavirus outbreak in Wuhan, China, but the study’s authors say that its results would apply to any such disease and are relevant to the current outbreak.

The study, which is based on epidemiological modeling and data-based simulations, appears in the journal Risk Analysis.

The authors are Professor Christos Nicolaides PhD ’14 of the University of Cyprus, who is also a fellow at the MIT Sloan School of Management; Professor Ruben Juanes of MIT’s Department of Civil and Environmental Engineering; and three others.

People can be surprisingly casual about washing their hands, even in crowded locations like airports where people from many different locations are touching surfaces such as chair armrests, check-in kiosks, security checkpoint trays, and restroom doorknobs and faucets.

Based on data from previous research by groups including the American Society for Microbiology, the team estimates that on average, only about 20 percent of people in airports have clean hands—meaning that they have been washed with soap and water, for at least 15 seconds, within the last hour or so.

The other 80 percent are potentially contaminating everything they touch with whatever germs they may be carrying, Nicolaides says.

“Seventy percent of the people who go to the toilet wash their hands afterwards,” Nicolaides says, about findings from a previous ASM study. “The other 30 percent don’t. And of those that do, only 50 percent do it right.”

Others just rinse briefly in some water, rather than using soap and water and spending the recommended 15 to 20 seconds washing, he says.

That figure, combined with estimates of exposure to the many potentially contaminated surfaces that people come into contact with in an airport, leads to the team’s estimate that about 20 percent of travelers in an airport have clean hands.

Improving handwashing at all of the world’s airports to triple that rate, so that 60 percent of travelers to have clean hands at any given time, would have the greatest impact, potentially slowing global disease spread by almost 70 percent, the researchers found.

Deploying such measures at so many airports and reaching such a high level of compliance may be impractical, but the new study suggests that a significant reduction in disease spread could still be achieved by just picking the 10 most significant airports based on the initial location of a viral outbreak.

Focusing handwashing messaging in those 10 airports could potentially slow the disease spread by as much as 37 percent, the researchers estimate.

They arrived at these estimates using detailed epidemiological simulations that involved data on worldwide flights including duration, distance, and interconnections; estimates of wait times at airports; and studies on typical rates of interactions of people with various elements of their surroundings and with other people.

Even small improvements in hygiene could make a noticeable dent.

Increasing the prevalence of clean hands in all airports worldwide by just 10 percent, which the researchers think could potentially be accomplished through education, posters, public announcements, and perhaps improved access to handwashing facilities, could slow the global rate of the spread of a disease by about 24 percent, they found.

Numerous studies (such as this one) have shown that such measures can increase rates of proper handwashing, Nicolaides says.

“Eliciting an increase in hand-hygiene is a challenge,” he says, “but new approaches in education, awareness, and social-media nudges have proven to be effective in hand-washing engagement.”

The researchers used data from previous studies on the effectiveness of handwashing in controlling transmission of disease, so Juanes says these data would have to be calibrated in the field to obtain refined estimates of the slow-down in spreading of a specific outbreak.

The findings are consistent with recommendations made by both the U.S. Centers for Disease Control and the World Health Organization.

Both have indicated that hand hygiene is the most efficient and cost-effective way to control disease propagation.

While both organizations say that other measures can also play a useful role in limiting disease spread, such as use of surgical face masks, airport closures, and travel restrictions, hand hygiene is still the first line of defense – and an easy one for individuals to implement.

While the potential of better hand hygiene in controlling transmission of diseases between individuals has been extensively studied and proven, this study is one of the first to quantitatively assess the effectiveness of such measures as a way to mitigate the risk of a global epidemic or pandemic, the authors say.

The researchers identified 120 airports that are the most influential in spreading disease, and found that these are not necessarily the ones with the most overall traffic.

For example, they cite the airports in Tokyo and Honolulu as having an outsized influence because of their locations.

While they respectively rank 46th and 117th in terms of overall traffic, they can contribute significantly to the spread of disease because they have direct connections to some of the world’s biggest airport hubs, they have long-range direct international flights, and they sit squarely between the global East and West.

For any given disease outbreak, identifying the 10 airports from this list that are the closest to the location of the outbreak, and focusing handwashing education at those 10 turned out to be the most effective way of limiting the disease spread, they found.

Nicolaides says that one important step that could be taken to improve handwashing rates and overall hygiene at airports would be to have handwashing sinks available at many more locations, especially outside of the restrooms where surfaces tend to be highly contaminated. In addition, more frequent cleaning of surfaces that are contacted by many people could be helpful.

Effective hand hygiene (HH) is important in preventing disease transmission in the clinical setting and community.

The handwashing behaviour of the general public and its effect on illnesses are issues of growing importance [14].

Whether people can practice HH properly is uncertain. Many people overlook the importance of HH when engaging in activities that require handwashing.

For example, < 40% of petting zoo visitors wash their hands upon exiting animal contact areas [2].

Handwashing with soap (HWWS) is the most effective way of removing pathogens from hands and preventing the spread of infectious diseases [57].

However, in a cross-sectional comparative study conducted in Bangladesh, a gap between perception and practice of HWWS was identified.

In the study, majority of the respondents (90%) have knowledge about the importance of performing HWWS before eating and after defaecation, but only 21% and 88% respondents reported to do so, respectively [4].

Certain sociodemographic factors are associated with HH compliance. In an observational study, people who lived in urban districts, with high educational level and sufficient knowledge on infectious diseases have a high handwashing compliance rate [8].

Women are more likely to wash their hands than men after controlling for washroom characteristics and clustering effects associated with social norms [9].

In an experimental study by using unobtrusive observation of human behaviour, the presence of other people in a restroom makes written messages placed in the room as a successful reminder of handwashing amongst males [10].

HH efficiency is a combination of washing efficiency and hand drying. Empirical evidence indicated that handwashing is approximately 85% effective in removing microorganisms on hands, and hand drying provides a further reduction in transient flora [7].

Inadequately dried hands are more likely to transmit microorganisms compared with completely dried ones [11].

In comparison with scientific evidence associated with HH compliance amongst healthcare professionals [1214], information about knowledge level and HH behaviour of the general public is relatively limited.

Many studies have evaluated that HH behaviour focus on handwashing compliance and ignore the importance of hand drying [1348].

In a qualitative evaluation by using a grounded theory approach to understand hand drying practices amongst the public in Kenya, hand drying on a clean towel was found as an uncommon practice amongst the participants.

Most women tend to dry their hands on their waist clothes when performing household chores, whereas men dry their hands on their trousers or a handkerchief [15].

Therefore, gender differences on preferred hand drying methods and the compliance of proper hand drying should be explored.


In general, the majority of the respondents can differentiate the diseases associated with poor HH, with female respondents having a better overall knowledge on HH than males (9.38 vs 9.06 out of 12).

The misconceptions of the respondents related to HH were identified. For example, the majority of the respondents misunderstood that always keeping the hands clean may lower the body’s defence mechanism, hands should be held under water while lathering, water temperature may induce a difference in the cleaning effects of hand cleaning and lathering for 10 s before rinsing is enough for hand disinfection.

In fact, the time taken for handwashing and degree of friction generated during lathering are more important than water temperature in removing dirt and microorganism, and warm water causes skin irritations and is not environmentally friendly [72425].

The inadequacy in the knowledge level is also in accordance with the self-reported practices of the respondents.

Only 12.8% of the respondents indicated that they generally lather their hands with soap for ≥20 s before rinsing, with the percentages in female respondents slightly higher than those in males (14.9% vs 7.8%).

This finding agreed with an observational study conducted in Ghana, wherein the majority of the participants perform handwashing for < 5 s [9].

The results of the multiple regression analyses also indicated that females had a significantly higher knowledge score by 0.288 towards HH than males after adjusting for age and education level.

The age of 30–49 years old and high educational level were the protective factors for improved HH knowledge.

Although the majority of the respondents indicated that they perform hand cleaning under different specific situations, such as before and after cooking, before eating, after urination or defaecation, after disposal of garbage bag and after sneezing/coughing; they admitted that they only use water or, in rare occasions, use alcohol-based hand rub (ABHR) or wet wipes for hand cleaning instead of performing HWWS.

Empirical evidence suggested that HWWS reduces the incidence of diarrhoeal diseases, respiratory infections and influenza and has been ranked the most cost-effective intervention for disease control by breaking the chain of transmission [356910]. According to predictions, significantly higher number of female respondents than male ones expressed that they performed HWWS than using water only (p < 0.001) in all critical moments. Nearly half of the respondents believed that 40% alcohol is sufficient for hand disinfection by using ABHR. However, ABHR does not kill all types of germs, such as norovirus, Clostridium difficile and some parasites; thus, it is not recommended for use when the hands are visibly dirty or greasy, such as after gardening or doing outdoor activities [24].

Significantly higher number of males than female ones ignored handwashing if they are in a hurry, when nobody is in the washroom or when they only urinated. Aunger [6] also reported that factors such as business, tiredness or hunger can discourage male respondents from performing HH behaviour in their study.

HH behaviour may be affected by others in the washrooms at the same time due to clustering effect [9]. HH is considered a social norm that is an effective driver to follow other’s behaviour in a relevant social group [56]. Similarly, females’ high compliance can be also associated with their tendency to practice socially acceptable behaviour [26].

Female respondents have a habit of wearing ring(s), artificial/acrylic nails or bracelets. Conversely, more males than females have a habit of wearing a watch. The bacterial load was 2.63-fold higher on ringed hands than on nonringed hands significantly [2728].

Wearing rings other than a wedding ring, a bracelet or a watch and having long nails were associated with poor HH amongst hospital workers [29]. Therefore, the public should be reminded to pay special attention to these regions during handwashing.

Over 70% of the respondents perform HH often during infectious disease outbreaks. The association between HH behaviour and H1N1 or SARS pandemics suggested that public education campaigns are effective in altering HH behaviour during the peak periods of outbreak occurrences [30].

With regards to hand drying, more males than females dry their hands on their own clothing, whereas more females dry their hands through air evaporation than males. Drying hands on dirty clothes can compromise the benefits of handwashing [15].

Hands that are inadequately dried are more likely to transmit microorganisms when compared with those that have been completely dried [11]. Over half of the respondents rub their hands when using a warm hand dryer.

The manner by which users place their hands under the hand dryer may also affect the number of remaining bacteria on hands. Yamamoto et al. [31] used a contact-plate method to evaluate the effects of hot air dryers when the hands are rubbed together or stationary.

The rubbing process may tend to draw out commensal bacteria to the skin’s surface from deep inside the pores and under the fingernails. However, additional scientific evidence should be gathered to verify this causal relationship.

The most often adopted methods for hand drying of the respondents were the use of paper towels, followed by warm hand dryers, jet hand dryers and cloth towel rolls. Similar to the results of previous studies, paper towel is the most common hand-drying method [532].

Paper towels can effectively dry hands, remove bacteria and cause less contamination in washrooms [33]. However, the use of paper towels can have adverse effects on waste disposal and environmental sustainability [34].

By contrast, conventional hand dryers have less environmental impact than paper towels [34]. However, conventional hand dryers are much slower than paper towels or jet hand dryers, taking approximately 45 s to eliminate only 3% of residual water [11].

The average time for using warm hand dryers was generally inadequate amongst respondents, with the majority of the respondents using ≤10 s when using warm or jet hand dryers. As a result, a significant amount of water remaining on the hands may easily recontaminate the hands after touching the surface environment, such as door handles upon leaving washrooms.

More female respondents than males tend to use paper towels to turn off a faucet or use water to splash the faucet before turning it off to avoid recontaminating the hands after washing. However, this practice can increase the use of water and paper towels [24].

Hands-free faucet with motion sensor, doors with automatic control or even washrooms without doors were recommended.

The findings of this cross-sectional study contributed to the understanding on the knowledge gap and public behaviour towards HH and the gender differences towards this issue. This information can inform gender-specific health promotion activities and creative campaigns to improve HH compliance and achieve sustained improvement in HH practices.


This study has some limitations. HH is a socially desirable and morally laden behaviour. Therefore, the respondents may over-report the situation. Future studies that will adopt the nonobtrusive monitoring of HH behaviour may be conducted to provide an unbiased evaluation of actual behaviour.

The network of the research team used convenience sampling. A relatively high percentage of the respondents attained tertiary education or above which may have an effect on HH behaviour.

Quota sampling that takes into account age distribution and socioeconomic status may be considered in future surveys for a representative sample. Sanitation and facility in washrooms are the major factors affecting people’s handwashing practices [435].

Future studies should be carried out to understand how washroom facilities can induce HH behaviour. HH knowledge and practices may also vary according to ethnicity and its associated washroom facilities. A wide-scale survey that compares the knowledge and HH behaviour of people residing in underdeveloped, developing and developed countries should be conducted to understand this topic from an international perspective.


The study results showed that female respondents generally have a better knowledge level and more favourable HH behaviour than male ones. Being a female, middle-aged and having tertiary education level were the protective factors for improved HH knowledge. Misconceptions related to the concepts that are associated with HH were noted amongst the public.

The most often adopted method for hand drying of the respondents was the use of paper towels. Self-reported practice on hand drying methods indicated that additional education was needed. The findings of this epidemiological investigation can provide information to gender-specific health promotion activities and creative campaigns to achieve sustained improvement in HH practices.

More information: Christos Nicolaides et al. Hand‐Hygiene Mitigation Strategies Against Global Disease Spreading through the Air Transportation Network, Risk Analysis (2019). DOI: 10.1111/risa.13438


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