COVID-19 clusters by March 31, 2020, Japan

TANAKA Sigeto

- data and script

TANAKA Sigeto <http://tsigeto.info>
(Graduate School of Arts and Letters, Tohoku University)

(2025-03-15)

Title: COVID-19 clusters by March 31, 2020, Japan || 2020年3月31日までに日本で発見されたクラスター
Author: TANAKA Sigeto || 田中重人
Version: 2
Date: 2025-03-15
Language: ENG
OSF: https://osf.io/52nvs

URI: http://tsigeto.info/covid19/cluster25.html
OSF project: https://osf.io/52nvs

Files

Details for the 25 COVID-19 clusters detected during January-March 2020 in Japan:

The same data are deposited on the Open Science Framework site: {doi:10.17605/OSF.IO/52NVS}.

Explanation

This list is based on a map (https://warp.da.ndl.go.jp/collections/info:ndljp/pid/11537253/www.mhlw.go.jp/content/10900000/000618504.pdf) (April 2, 2020) by the Ministry of Health, Labour, and Welfare (MHLW) plotting “clusters” that were roughly defined as five or more COVID-19 cases coming in contact at a common venue as of March 31, 2020.

Each record includes information from reports from the MHLW and municipalities, mass-media news, academic papers, and so on [Source].

Estimated date when the cluster infection occurred [Date(occurrence)]
Date when a case in the cluster was first identified [Date(1st)]
The process of tracing to find the cluster [Direction]
Date when the fifth case in the cluster was identified [Date(5th)]
Number of cases including the entire known network of the infection chain connected to the cluster [Size]

As for the process of tracing [Direction], the chronological order between the time when the known cases showed any COVID-19 symptom and the time when they contacted those whom the tracer tracked to find the cluster was classified into three catetogies:

After: contacts after the symptom onset
Before: contacts before the symptom onset
Mix: both of them

For each cluster, the identification number [ID] is nine-digit code: five digits for municipality and four digits for the date when the cluster was identified, concatenated with a hyphen.

Although the map plotted 26 clusters, one in the Gunma Prefecture was omitted from the list, because it was mistakenly reported (according to Jomo Shinbun https://www.jomo-news.co.jp/articles/-/21600 April 5, 2020). The list thus contains 25 clusters.

As for the number of cases [Size], all cases linked to the network of infection chain including the cluster was counted, expect for cases that were reached by tracing from other cluster. Those detected in April 2020 were included. If the information sources reported different numbers, the largest number was used.

History

2022-05-29: A preliminary version (Version 0) was prepared for a presentation in the 73rd annual meeting, Kansai Sociological Association ({http://tsigeto.info/22x}, in Japanese).
2023-03-14: Version 1 was stored on Open Science Framework {DOI:10.17605/OSF.IO/52NVS}.
2025-03-15: Version 2. Files on Open Science Framework {DOI:10.17605/OSF.IO/52NVS} was updated.

Works

Version 0 was used for: [* The reported number of COVID-19 cases and its interpretion as official statistics: The changing connotation of “cluster”] at the 73rd Meeting of Kansai Sociological Association (2022-05-29)
Version 1 was used for: Was Japan's cluster-based approach toward coronavirus disease (COVID-19) a fantasy?: Re-examining the clusters' data of January-March 2020. Research Square (Preprint). {doi:10.21203/rs.3.rs-2647575/v1} (2023-03-17)
Version 2 was used for: [* Revisiting facts from a few years ago: fictiousness of Japan's “cluster-based approach” toward COVID-19] at Japanese Studies Workshop, 2025 Conference (2025-03-16)
Version 2 was used for: Was Japan's cluster-based approach toward coronavirus disease (COVID-19) a fantasy?: Re-examining the clusters' data of January-March 2020. Annual Reports of Graduate School of Arts and Letters, Tohoku University. 75:96-83 (2026-03-12)

Communication

Questions/comments are welcome.

Related sites and pages

Tohoku Univ / School of Arts and Letters / Innovative Japanese Studies / TANAKA Sigeto

History of this page:

2026-03-21:Created
2026-03-22:Revision

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