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viruses33). The Center for Disease Control and Prevention recommends a ventilation of 6-15 room air changes per hour to minimize the transmission of microbes33). However, the efficient ventilation of room air is accompanied by unwanted warming or cooling of room air unless an ambient temperature is appropriate. This requires extra energy expendi-ture aside from that required for mechanical venti-lation, and such procedures go against the earth-warming policies of many countries. Thus, the safe and effective inactivation of viruses in room air by methods other than ventilation should consider energy saving. In summary, after a survey of the current literature, low-concentration chlorine dioxide is the most suitable agent for the safe and effective.Ozone gas is an effective disinfectant in the air. However, its toxicity becomes a serious problem when it is used continuously in a room5-7). On the other hand, chlorine dioxide gas can be used in a room with low concentrations that are effective in inactivating viruses and which are safe to humans18). Chlorine dioxide gas is the only practical and currently available disinfection agent that can disinfect viruses in room air to prevent viral respi-ratory diseases34).Since ethical support is required when using chlorine dioxide gas in a manned environment, there was a need to obtain approval from the ethics committee of hospital and institution. We installed and applied in an actual hospital environment after careful consideration and discussion by the committee and their approval. After that chlorine dioxide gas generating gel was installed in each room of the pediatric ward in a city hospital during the winter months when infectious gastroenteritis was prevalent, and we were able to conduct a study on the effect of preventing secondary infec-tions of the infectious gastroenteritis using an aqueous solution of chlorine dioxide. As a result of examination of the four seasons since 2016, it was confirmed that there were no secondary infections of infectious gastroenteritis observed and that there were no reported adverse events. (Figure 1)in patient around 48 hours after admission. This form of pneu-monia has a high mortality rate and incidence rate and is a major problem in terms of the medical Nosocomial pneumonia develops expenses it incurs for patients. One of the preven-tive measures for nosocomial pneumonia includes environmental improvement such as disinfection and cleaning of hospital rooms. However, in many ways, this is an uphill battle, as many infections are transmitted through droplets in the air (as we have seen with the recent COVID-19 pandemic), which are extremely difficult to combat, especially when the main preventive method is cleaning surfaces.In nosocomial infections, contact infections such as drug resistant bacteria and viruses become a problem. Furthermore, measures such as ventila-tion of air-conditioning and prevention of aerosol spread by shielding are being taken as measures against aerosol infection and air infection. Standard precaution measures alone leave viruses and bacteria in the environment. Secondary infections also occur in actual medical settings, making it diffi-cult for clusters to occur. It is possible to further reduce the risk of nosocomial infections by adding more reliable infection countermeasure in spatial disinfection and virus removal using chlorine dioxide gas to the conventional infection countermeasures. And the causative microorganisms include not only general bacteria but also drug-resistant bacteria, such as Methicillin-Resistant Staphylococcus aureus (MRSA) and Multi-Drug Resistant Pseudomonas aeruginosa (MDRPA). (Figure 2)Of course, measures already exist within hospi-tals to prevent or counteract air and droplet infec-tions. One of the chief methods is the use of high-ef-ficiency particulate air (HEPA) filters, but even if the pathogenic microorganisms are captured by the filter, they are not sterilized or killed - meaning that the problems are not really solved in any meaningful way. There are also problems with the associated costs of HEPA filters, as well as the issues they cause regarding the need for secure spaces in hospitals - something difficult to achieve when HEPA filters are installed.On the other hand, chlorine dioxide exists as a gas at room temperature and dissolves in water to form an aqueous solution. Chlorine dioxide gas and aqueous solution have a sufficient effect on aerosol infection of the causative microorganism for noso-comial pneumonia and an improvement of its effi-cacy can be expected by using it in combination with the conventionally used HEPA filter.467Discussion