Abstract
From January 18, 2022 to April 17, 2022, we recorded the daily number of infected people during the COVID-19 Omicron strain epidemic (6th wave) that occurred in Niigata Prefecture by 9 facilities and 12 prefectural public health centers, and Niigata City, which is an ordinance-designated city, and analyzed the occurrence of these clusters. There are nine categories of facilities: kindergartens, schools, facilities for the elderly, welfare facilities, companies, medical facilities, sports facilities, government offices, and restaurants.
As a result, when looking at each facility where clusters occurred, the total number of infected people, the number of consecutive days, and the maximum number of people per day differed greatly. There have been cases of explosive increases in the number of infected people in kindergartens, schools, welfare facilities, and companies, and there have also been cases of long-term infections in kindergartens, schools, facilities for the elderly, and welfare facilities. We confirmed the importance of taking proactive measures such as accurately capturing the initial movement and suppressing clusters early.
Tracking clusters of 5 people was effective in capturing about half of the total number of infected people who occurred, but if the cluster size is 10 or more people, the mesh is too large and the capture rate is extremely low. However, it was found that it was inadequate to suppress the infection.
Omicron strains often remain asymptomatic or mild cases, making it difficult to confirm the chain of infection. However, it was confirmed that the chain of infection would not be maintained unless a cluster was formed, and it is considered that measures against clusters in Niigata Prefecture have achieved a certain degree of success under difficult circumstances.
