National

Japanese cluster study revives ‘3Cs’ warning as coronavirus cases surge anew

by Satoshi Sugiyama

STAFF WRITER

Amid a jump in coronavirus cases over the past few days, a new study is offering a fresh warning that infections continue to be prevalent in closed environments without adequate ventilation, including entertainment venues, restaurants and gyms.

The study examined 61 clusters of COVID-19, the respiratory illness caused by the novel coronavirus, based on 3,184 cases between January and April this year. A cluster is defined as five or more cases reported in the same place, with the largest so far involving over 100 cases at a hospital.

The study, compiled by Japanese researchers, was published this month in a journal by the United States Centers for Disease Control and Prevention.

Of those clusters, 18 were found at health care facilities, 10 at day care centers and nursing homes, and another 10 at restaurants and bars. Workplaces, music events — including karaoke parties — and gymnasiums were also sources of clusters.

Those places meet the criteria for the “Three Cs”: closed spaces with poor ventilation, crowded and close-contact settings — a situation that the government says creates a higher risk of exposure to the virus.

“We noted many COVID-19 clusters were associated with heavy breathing in close proximity, such as singing at karaoke parties, cheering at clubs, having conversations in bars, and exercising in gymnasiums,” the researchers, including Dr. Yuki Furuse of Kyoto University, wrote in the journal.

The study coincidentally warned that infections are becoming prevalent among younger generations and that they may be spreading the virus without realizing it.

Analyzing 22 probable cases where clusters not related to hospitals originated, the researchers found that half of those infected were between the ages of 20 and 39 — a demographic younger than the age distribution for all COVID-19 cases reported in Japan.

“We also noted probable primary COVID-19 case-patients appear to transmit the virus and generate clusters even in the absence of apparent respiratory symptoms, such as cough,” the researchers wrote.

The number of newly reported cases in Japan has been steadily increasing since the nationwide state of emergency was lifted on May 25 and the country gradually returned to a semblance of normalcy.

On Saturday, Tokyo confirmed 57 new cases — the highest daily figure since the emergency declaration was rescinded.

A day earlier, the nationwide figure exceeded 100 for the first time since May 9, with Tokyo reporting more than 45 cases for three consecutive days. Nearly 60 percent of the cases in the capital on Friday were associated with the nightlife industry and 74 percent were people in their 20s and 30s.

Despite the rising toll, Tokyo Gov. Yuriko Koike denied it was a sign of an emerging second wave of infections.

Public health experts have credited Japan’s vigorous cluster-tracing ability with keeping infections relatively low compared with other countries. As of Friday, more than 18,300 people had been infected and about 970 had died.

“Detecting clusters of cases can lead to effective quarantine of close contacts and to the identification of risk factors for the formation of such clusters,” the researchers wrote.

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