Project Responds to Pandemic Threat

Preventing pathogens from entering the human body is a crucial step in infectious disease prevention. The transmission of pathogens that cause respiratory tract infections like the novel coronavirus (also known as SARS-CoV-2) and influenza can be respiratory (droplets) or airborne or it can be through direct contact. Various studies have greatly advanced our understanding of the infection risks posed by droplet and airborne transmission. However, the pathways and risks of direct contact infection—that is, how viruses on the fingers and other body parts might transfer to furniture, objects, and other people's fingers before traveling to such mucous membranes as the nose and mouth—were not entirely understood. Therefore, the research group launched a project with an eye to preventing the future possible spread of infectious diseases by creating a visualization of infection risks in the home in order to support the establishment and practice of proper hygiene habits. The project set out to provide an accurate understanding of contact infection risks by focusing on the behavior of consumers upon returning home—i.e., situations wherein viruses are likely to be brought in from outside—based on which the group created visualizations based on observations of the unconscious behaviors of consumers up to the point of washing their hands. Mr. Takizawa, the group’s lead researcher, explains the reasoning behind the project.

“As a group that studies microorganisms like viruses and bacteria, we examine the properties of the virus itself in a laboratory setting. However, what is of great concern to many people is where a virus comes from and how it is spread. To understand that, we must combine our studies with studies of human behavior. ”

A project was thus launched to build a simulation model that visualizes virus infection risks in the home.

Visualization of Virus Adhesion and Spread

To develop a simulation model that analyzes the way viruses disperse and spread in the home upon a resident’s return from outside, the acquisition and incorporation of two major types of data was necessary. The first type being data on the extent of virus dispersal on material surfaces in the home (virus dispersal data), and the second type being data on residents’ behavior upon returning home (i.e., their contact with furniture, movements within and between rooms, etc.).

To obtain data on virus adhesion and dispersal, we established a reference utilizing the properties of an experimental-use, low-virulence influenza strain that, like COVID-19, is an envelope-type virus.*¹ Taking into account the fact that the composition of furniture and other objects found in the home varies widely, we tested several materials, including plastics, metals and cloth, and adhered the virus to models simulating skin surfaces.

We then assessed the spread of the virus from the simulated skin models to each material surface and from the material surfaces to the skin models. The results confirmed that the virus dispersal rate from the skin models to the material surfaces was higher than from the material surfaces to the skin models.

^{*1 A virus enveloped in a lipid bilayer.}

Furthermore, upon returning home, residents are expected to engage in behavior entailing their continually touching various objects. In order to confirm the change in the transfer efficiency due to this contact, we evaluated the effect of the contaminated skin model coming into repeated contact with the entry doorknob (stainless steel surface), which is almost always touched when entering the home. As a result, it was confirmed that transfer efficiency decreased significantly according to the number of times contact with the knob was made.*² These results were reflected in the virus dispersal data for the simulation model construction.

^{*2 Sekine, Y., et al: “Visualization of the Risk and the Care Effects on the Viral Contact Infection in the Home,” The Japanese Society for Artificial Intelligence, 38(2): 2023 [Japanese only]}

Mr. Nakajima, who was in charge of virus adhesion and dispersal, says, “Since this was Lion's first effort, it was really challenging to establish all the variables regarding experimental conditions in a short period of time, including the conditions enabling contact with the virus and how to detect it.”

In parallel with virus adhesion and dispersal, data on the behavior of residents when returning home were obtained. Typically, residents are unconscious of many of their movements and much of what they touch. To understand actual behavior from the time a resident returns home to the time they wash their hands, we conducted a survey of approximately 1,100 men and women to determine the typical shape and layout of residences, the rooms usually visited within the 30 minutes immediately following their arrival home, the order in which they touch objects and the timing of hand washing and sanitizing. This allowed us to quantify contact behavior and indoor movement within the home.

“In the beginning, we had no idea what criteria to use for data gathering given individual variations in home layouts and residents’ behavior upon returning home. After extensive discussions with our co-researcher, Professor Setsuya Kurahashi,*³ who has experience in analyzing various human behaviors and social trends through simulations, we designed the survey, obtained the data necessary for developing the simulation model and proceeded with the analysis.” (Mr. Nakijima, Researcher)

^{*3 Affiliation at the time of development: Professor of Business Science, University of Tsukuba}

What Our Visualization of Residents’ Behavior When Returning Home Revealed

An agent-based model was constructed based on the acquired data on viral adhesion, dispersal and residents’ behavior upon returning home. This made it possible to quantitatively visualize the estimated viral loads adhering to objects or fingers in the rooms visited by consumers as well as the spread of the virus throughout the residences.

Using an agent-based simulation constructed based on previous data, the following figure reproduces the typical behavior of an adult in the first 30 minutes after returning home. It is assumed that before their return to the home the individual’s fingers were contaminated with the virus and that no hand washing or other hygiene behavior was performed after contamination. The results of the analysis suggest that the viral load transferred to objects is higher in rooms with objects that are touched soon after the individual’s arrival, such as doorknobs and remote controls, while the viral load brought into bedrooms and western-style rooms is lower.

In addition, we compared the spread of the virus when hand washing and hand disinfection were performed after the resident’s return but before touching objects. Results showed that hand washing soon after returning home reduced the extent of viral spread, and that hand washing and hand disinfection at the entrance was particularly effective.

Based on previous findings, the research group also suspected that adults and children tend to behave differently in the home and touch different things. Therefore, in order to clarify the effects of hygiene habits on viral spread by adults and children, a simulation model for children was also constructed and analyzed. Assuming a situation in which a child's fingers are contaminated before their return, but the adult is virus free, the model projects that if a child returning home alone earlier and an adult returning home later both fail to practice properhygiene, the virus will spread throughout the household.

Conversely, it was hypothesized that the indoor viral spread by a child before the return home of an adult could be greatly reduced by these children practicing proper hygiene habits.

Furthermore, to estimate the risk to the adult of secondary contact infection, we analyzed the viral loads adhering to the hands of an adult returning home after a child who returned home first had practiced properhygiene habits. Similarly to the above scenario, we assumed a situation in which viruses had adhered to the fingers of the child before they returned home, but not to the hands of the adult. Results showed that the hygiene behavior of a child who returns home first alone may not reduce the risk of secondary contact infection in a later returning adult. In fact, the viral load was almost the same as if neither the adult nor the child had practicedproper hygiene habits. It was concluded that this is due to a large viral load on the front doorknob, which was touched by the returning child prior to their practicing proper hygiene habits. So, the virus will transfer to the hand of the later returning adult.

On the other hand, it was suggested proper hygiene habits practiced by both the child returning home first and the adult returning home later could significantly reduce the viral load on the hands of the adult, thereby reducing the risk of secondary infection. This suggests the importance of all family members practicing proper hygiene habits at the appropriate time when they return home in order to reduce the risk of infection in the home.

Project member and researcher Mr. Kato commented on the significance of the results of this study as follows.

“Our research has shown that infection risks can be reduced if all family members touch as few indoor objects as possible immediately after returning home and are quick to practice proper hygiene habits. By disseminating the results of this research to consumers, we hope to contribute to the fight against infectious diseases. We also hope that the results of this study will encourage consumers to take a fresh look at their own unconscious habits.”

Rather than being unduly afraid of unseen germs or underestimating infection risks, combatting infectious diseases by engaging in and developing proper hygiene habits is crucial. Researchers will continue taking on the challenge of conducting research and developing products that will contribute to the realization of this goal.

Contents, and affiliations are as of the time of the interview. (Interviewed Jan 2024)