COVID-19 infection has been reported to be caused by droplet and contact infection. This paper proposes a model that visualizes the risk of contact infection to family members when viruses spread to various items at home. Behavior data after returning home are extracted from a questionnaire-based survey of home behavior to design the agent-based model. The data tables of contact behavior are created, including the room-to-room transfer probability table, the conditional probability table, and the contact probability table. The material transfer efficiency table is also created by measuring the virus transmission rate after contact with droplets in a virus experiment laboratory. In the experiment, the synthetic agent created from the acquired data probabilistically performs movement and contact behavior after returning home and reproduces the state in which the virus attached to the hand or belongings, when going out, propagates to objects at home. Next, we examine the risk of a second family member returning home. As a result, virus-attached contacts within around 30 minutes after returning home are widely confirmed around the entrance and kitchen, suggesting the effectiveness of early hand-washing behavior. And the experiment shows that even if the first person returning home disinfects their hands inside the entrance, the virus remains in a part of the entrance, and the virus is spread inside the room by the second person returning home.

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Quaternary cationic surfactants with bactericidal activity such as didecyldimethylammonium chloride (DDAC) show an inactivation effect on enveloped viruses, but they have little effect on non-enveloped viruses such as noroviruses. Therefore, we examined additives that enhance the inactivation effect of cationic surfactants by using feline calicivirus (FCV) as a representative of a non-enveloped virus. The result was that SO42- ions, which are a general-purpose salt, had a strong salting-out effect that reduced the solubility of proteins, greatly enhancing the inactivation ability of DDAC. The SO42- ions also enhanced FCV inactivation by other cationic surfactants such as cetylpyridinium chloride (CPC) and benzalkonium chloride (ADBAC). To clarify the mechanism, we evaluated the denaturation and binding process of DDAC to bovine serum albumin (BSA) as a model protein by means of circular dichroism (CD) spectrum and isothermal titration calorimeter (ITC), respectively. The SO42- ions disturbed the protein structure by their salting-out effect and promoted cooperative binding from lower DDAC concentrations by reducing the critical micelle concentration (cmc), indicating that these synergistic effects caused a large structural change in the protein. These results suggested that increasing the protein denaturation of the cationic surfactants by adding SO42- ions enhanced the inactivation effect on the non-enveloped virus.