Equivocality of the term 'cluster' in Japan's COVID-19 response

Changes in 2020
TANAKA Sigeto <http://tsigeto.info>
(Graduate School of Arts and Letters, Tohoku University)
Bunka 86(3/4):239-219, 208 (2023)

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URI: http://tsigeto.info/23a
OSF project: https://osf.io/tnz3h
Blog entry: https://remcat.hatenadiary.jp/entry/20230907/23a

Abstract

“Cluster” is a term characterizing Japan's response to the outbreak of the novel coronavirus disease (COVID-19) in early 2020. Its usage is often confusing considering its multiple meanings. This study examined relevant literature, including government documents and media news, to explore the usage of the term between February 2020 and January 2021.

The results show that the government and experts started using the term with three connotations in late February and early March 2020: (A) large-scale infection caused by one infector (super-spreader), (B) a chain of infection that can potentially expand, and (C) large-scale infection caused at a place or an event (group infection) regardless of the number of infectors. The use of the term with meaning A has since disappeared, while meanings B and C survived. The active surveillance system has consistently used meaning B. Meanwhile, local governments have used meaning C since early June 2020 with the concrete criterion that five or more cases should be involved, after some discrepancy in the earlier period. The central government once adopted the same usage, but subsequently showed a discrepancy by using meanings B and C interchangeably. Moreover, it expanded meaning C to include small-scale infections with four or fewer cases (C').

This change in the usage of the term reflects a latent change in the strategy of the government and its advisory experts. Focusing on defense against super-spreaders as their primary efforts to curb the spread of infection, they used the term “cluster” to connote super-spreaders in meaning A in the early stages of COVID-19. However, during the prolonged COVID-19 pandemic, they implicitly shifted their focus to chains of small-scale infections. In order to determine the risks of infection of daily activities (eating and drinking in particular), they collected case reports of small-scale infections that they referred to as “cluster” in meaning C'. Therefore, “cluster” no longer represented the threat itself, but rather denoted a framework to determine cases representing activities with a certain level of risk that would not cause large-scale infection but could contribute to the spread of COVID-19 in the aggregate through several small-scale infections.

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