NAGOYA -- A series of novel coronavirus infections among a group of special kendo trainees in the Aichi Prefectural Police was certified as a cluster infection by the prefectural government on April 7. In response to the infections, the All Japan Kendo Federation has released an emergency statement warning people to refrain from engaging in the sport at this time.

It appears that transmission was exacerbated by the poorly ventilated "dojo" training hall where the special trainees practice, and that the characteristics of the kendo sport itself may have played a part due to it often putting practitioners into the dangerous "three Cs" circumstances of confined spaces, crowded places and close contact with people.

When kendo practitioners train together, they generally do so facing one another. It's thought that the risk of infections from the sport could be high due to many dojos being poorly ventilated spaces in which many people gather together, and from the increased chances of airborne transmission caused by the customary shouting practitioners do in kendo.

A member of the All Japan Kendo Federation based in Tokyo's Chiyoda Ward agreed that the martial art does carry extra risks, saying, "When training, there are times when practitioners' faces come as close as around 30 centimeters apart from each other. It's easier for droplet transmission to occur in this sport."

The kendo trainees at the police force are part of a group of specialists aiming to become instructors in the martial art. In the case of the Aichi Prefectural Police, their kendo group is made up of 22 people including practitioners in their 20s and 30s who make appearances at national tournaments and instructors. The training forms part of their duties on the job.

According to the prefectural government, in late March there were continual cases of trainees showing symptoms including fevers and fatigue. But in each instance the doctor who saw them was described as saying that the chances of them having contracted the coronavirus were low, and because they didn't have pneumonia it was probably just a cold. It was also judged that the number of absences from work was within ordinary parameters, and the kendo training was reportedly allowed to continue.

But on March 31 kendo practice was canceled completely after the number of staff asking to be allowed to take time off due to ill health shot up to seven people. On April 1, two men in their 20s and 30s in the riot police unit became the first of more confirmed positive cases. By April 7, a total of 18 men and women who are special trainees had tested positive for the novel coronavirus.

The virus is known to have spread farther than the prefectural police's kendo group. Two male university students who took part in training with the special trainees were also found to have been infected with the virus, and another nine family members and acquaintances of the trainees were also confirmed to have the virus.

The original route of infection is unknown. Currently, over 100 police officers who may have had close contact with the special trainees are self-isolating at home. Prefectural police say that at present the events surrounding the infections have not had an effect on their ability to work and pursue cases.

But a top official at the force commented, "Kendo and judo practice are part of police officers' daily routines. We take this (cluster infection) very seriously, and wish to prevent the further spread of infection beyond the special trainees."

(Japanese original by Kristina Gan and Kazuki Sakuma, Nagoya News Center)