It has widely been recognized in the infection disease community that airborne transmission by viruses and bacteria can be controlled by proper ventilation. Therefore, consumer CO₂ sensors have been widely used for infection control in COVID-19. In this paper, the author has discussed the measurement and control of CO₂ concentrations as a countermeasure against infectious diseases based on mathematical models, laws and standards, and has presented field studies and intervention cases including actual sites where clusters have occurred. As a result, the author has proposed that four phases of effective use of CO₂ sensors are important: selection, installation, visualization, and ventilation measures. In particular, visualization of CO₂ concentrations has been expected to become more widespread because it is an effective means of making risks apparent and raising awareness of airborne transmission control among the general public.

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Among the main routes of transmission of infectious diseases, infection by large droplets can be prevented by increasing the distance between people. Transmission by inhalation of aerosols can be prevented by ventilation. Several guidelines suggest the use of CO₂ concentration as an indicator to determine the actual status of ventilation. Herein, a novel system for real-time monitoring of infection risk has been developed. This system displays the infection probability distribution in real-time based on the CO₂ concentration and the positional information of the occupants. A demonstration experiment of this system was conducted in an actual office, and the results were reported, which confirmed that the system can quantitatively predict the probability of infection by integrating ventilation efficiency and social distancing of the occupants. Therefore, by introducing this system, evidence-based infection control measures can be taken according to the actual situation.

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With the spread of COVID-19 infectious diseases, fine particle visualization technology has been applied for the purpose of planning measures in various fields. We will outline the technology for visualizing droplet particles, and introduce the examples that has been measured the speed, reach, and behavior of suspended droplets, as well as the number of droplet particles in a clean room by using the technology.

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The modes of exposure to infectious aerosol particles and possible effective countermeasures are summarized, and the overview of the cough simulator developed to assess the risk of infection by respiratory droplets and aerosol particles is presented. As of November 2021, the number of infected people has increased again in developed countries. There is a possibility that further epidemic waves will occur in Japan, so it is necessary to continue implementing infection control measures until the epidemic is under control. In order to establish effective infection control measures, further research focusing on the effects of non-stationary, non-uniform indoor environments and air purification technologies is needed. This paper presents an overview of a simulated cough generator developed to assess the risk of infection by respiratory droplets and aerosol particles and describes experiments on droplets and aerosol particles conducted using the device.

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Infrared thermography attracts much attention for fever screening in the COVID-19 pandemic. It enables non-contact instant measurements of the skin temperature. Various infrared thermography systems have been deployed everywhere to check if a person has a fever or not. However, there are not so few reports that tell us problems with accuracy in the screening. In this article, basics of infrared thermography and its application to fever screening is reviewed. Cautions when using infrared thermography are also discussed on the basis of the relationships of the skin temperature versus body temperature and on the accuracy of radiation temperature measurements.

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